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NAME AND ADDRESS 

SJ~C{,o,o -pa~ \\Cl0 
f-CJ~\:J\11)11 577n'e, Co~ 
od/\ o~ V\ \tu 1/V\ ti wy') is 

f \rvi Gf?,vws ·1o50 

·DATE 



THE EFFECTS OF HIGH CONDUCTIVITY LIQUID FEEDS ON THE 
YIELD AND QUALITY OF OUTDOOR GROWN TOMATOES 

A Thesis Presented in Partial Fulfilment of the Requirements 
for the Degree of Master of Horticultural Science in 

Vegetable Production at Massey University 
Palmerston North, New Zealand 

EDGARDO F. FADALlAN 

Department of Plant Science 

1993 



ABSTRACT 

Studies were conducted to evaluate the effects of high conductivity liquid feeds 

applied using drip irrigation on the yield and quality of outdoor grown tomatoes. 

Seed of the tomato cv. Extase were propagated in cell trays. During propagation 

the seedlings were fed using a stock solution containing 100 ppm nitrogen, 34 

ppm phosphorous and 100 ppm potassium. The transplants were planted out on 

3 December 1991 in the Karapoti Sandy Loam soil at the Plant Growth Unit, 

Massey University. The spacing used was 150 cm between the rows and 60 cm 

2 in the row. A base maintenance dressing of Nitrophoska (12-16-10) fertilizer 

was applied at a rate of 500 kg per hectare banded 20 cm on either side of the 

row prior to planting. 

There were 3 conductivity treatments of 2, 4, and 6 mS cm-1 and a control 

treatment. A randomized complete block design was used with 4 blocks and 12 

plants per plot. The 3 conductivity treatments were based on a standard 

greenhouse liquid feed, while the control plant received water only. Irrigation 

requirements were calculated based on a crop factor, area per plant and potential 

evapotranspiration. Conductivity treatments oommenced at the stage were 50% 

of the plants had commenced flowering on the first truss. Conductivity treatments 

were applied every 2 days for 2 hours regardless of rain, while control plants 

were irrigated with tap water when soil moisture deficits exceeded 28 mm day-1 

except when rainfall immediately followed the scheduled irrigation. 



ii 

Plants were trained to 2 stems. The second stem was produced from the leaf 

axil immediately below the first inflorescence. The Otaki system of training and 

supporting tomato plants was used with the first support attached 25 days after 

planting and thereafter every 30 cm. Plants were delateraled regularly and 

stopped by removing the terminal buds at 2 metres high. 

Leaf analysis was carried out on 2 occasions, 30 and 55 days after planting, 

while the conductivity of the soil solution was determined at final harvest. Yield 

data was collected for each truss on a per stem basis per plant. Fruit were 

weighed individually and also size graded to the accepted commercial standard. 

From these data the number and weight of marketable and reject fruits were 

determined. Fruit samples were taken for 6 consecutive weekly harvests for 

compositional analysis. Firmness, total solids, titratable acidity and total soluble 

solids were measured from sample fruits from each treatment. 

Increasing the conductivity of the liquid feed increased the concentration of 

nitrogen and potassium in the leaves 30 days after planting, while phosphorous 

and magnesium were not affected by the treatments. Calcium fell with each 

increase in conductivity. At the reproductive stage (55 days after planting) the 

nitrogen, phosphorous and potassium content fell with increasing conductivity 

over the range of control to 4 mS cm-1
• Calcium and magnesium content also fell 

with increasing conductivity of the liquid feed. The conductivity of the soil solution 

increased as the conductivity of the liquid feed increased. As the distance from 

the dripper increased the conductivity of soil solution decreased. 



iii 

Tomato plants in this study supported an average of 13 trusses. There were 18 

harvests where fruits were harvested at a commercial acceptable stage of 

maturity and a 19th harvest was used to remove all the remaining fruit on the 

plant. The main stem carried approximately 65% of the fruit load. Conductivity 

treatments had no effect on the number and weight of fruit of individual trusses 

on the main stem except for the 4 mS cm-1 treatment which had a higher number 

and yield of fruit in the third truss. No explanation can be offered for this effect. 

There were no differences between treatments in the number or yield of fruit per 

truss on the lateral .stem. 

Neither the number or yield of marketable fruit or the total number or total yield 

of fruit at final harvest were affected by the conductivity treatments. There was 

however a trend for yield to decrease with the 6 mS cm-1 treatment. It is possible 

that if the experiment had been continued for a longer period a treatment effect 

on the number and yield of fruit may have been obtained. It was suggested that 

the heavy rain experienced during the experiment may have delayed the 

occurrence of a yield reduction. Although there was no significant effect of 

conductivity on fruit size, the number of fruit in the two largest size grades tended 

to be highest for the control plants, while the 6 mS cm-1 treatment had the 

smallest number of fruit in these size grades. This is further evidence that the 

conductivity treatments tended to have an effect on fruit size and thus yield. 

The main cause for fruits to be rejected was due to fruit cracking, which usually 

occurred when harvesting preceded heavy rainfall. 



iv 

The occurrence of blossom end rot was low since both rainfall and the regular 

application of liquid feeds did not place the plants under a fluctuating moisture 

stress. Overall there were very few rejects. 

The conductivity treatments increased titratable acidity above that of control 

plants, but there were no difference between the conductivity treatments. Over 

time titratable acidity of the fruit declined and this may have been associated with 

either a seasonal effect or the position of the fruit on the stem. Total solids was 

increased as the concentration of the liquid feeds increased. The percentage of 

total solids allocated to structural material fell as the concentration of the liquid 

feed increased. This suggests that the increase in the total solids was due to 

an increase in the soluble solid component. There was no effect of conductivity 

on fruit firmness, however firmness fell from an initial value at harvest 1. Total 

soluble solids of the fruit increased with each increase in conductivity. Over time 

the trend was for soluble solids to fall slightly up to harvest 5 with a marked 

decline occurring at harvest 6. 

As improvements in fruit flavour are associated with increases in titratable acidity, 

total solids and total soluble solids the conductivity treatments used in this 

experiment were successful in improving this aspect of fruit quality. This was 

achieved without any decrease in yield. As suggested however, a trade off 

between quality and yield may have occurred if the experiment had been 

continued for a longer period of time. 



V 

This research suggests that the use of trickle irrigation to supply high conductivity 

liquid feeds to field grown tomatoes has the potential to significantly improve fruit 

flavour. 



vi 

ACKNOWLEDGEMENTS 

Writing this thesis is an enormous task. As others know well, to bring a thesis 

from an image to reality requires a sustaining force. For me this had been 

achieved through the combination of prayers and graces of good health from our 

Almighty and support from those who are involved at various stages of the study. 

My indebtedness goes to Dr. Keith James Fisher, my chief supervisor for his 

expertise, guidance and constructive suggestions. He was very generous and 

patient spending much time editing, reviewing and proofreading the manuscript. 

I am grateful to Dr. Michael A. Nichols my second supervisor for his confidence 

and camaraderie during the entire course of this work. He was very kind and 

helpful looking after most of my statistical analysis. 

I also wish to express my heartfelt thanks and gratitude to the staff of Plant 

Growth Unit for their unceasing support during my experimental work. 

It also gives me a great pleasure to record my appreciation to the New Zealand 

government through the Ministry of External Relations and Trade for financing my 

study at Massey University . 

My profound gratitude is also extended to the Executive Board of Romblon State 

College for giving me the opportunity to pursue my postgraduate degree under 

the Overseas Development Assistance Programme. 



vii 

My special thanks to fellow ROSCOFEANS for wishing me good luck and 

success in my studies. I hope I have come close to living up to their 

expectations. 

The support and encouragement I received from all Filipino students at Massey 

University had been of paramount importance and to all of them I wish to express 

my sincere thanks. The help and moral support of the Carambas and Baker 

families during my stay in New Zealand is here most gratefully acknowledged. 

My special thanks to all staff and graduate students in Plant Science 

(Horticulture) for their friendship, humour and help to unravel some of the 

mysteries in computers. 

My heartfelt thanks are due to my parents, brothers and sisters, in-laws and 

relatives for their help in many ways. 

Finally, my deepest gratitude to my wonderful wife Eden and son Jake for their 

moral support and encouragement. Their love and patient understanding are the 

backbone of my success. 

To anyone whose help during my study I have failed to acknowledge, please 

forgive the oversight and accept my heartfelt thanks. 



TABLE OF CONTENTS 

ABSTRACT 

ACKNOWLEDGEMENTS 

TABLE OF CONTENTS 

LIST OF TABLES 

LIST OF FIGURES 

LIST OF PLATES 

LIST OF APPENDICES 

GENERAL INTRODUCTION 

CHAPTER 1. Review of Literature 

1.1 Introduction 

1.2 Plant Nutrition 

1.2.1 Response of Tomato Plants to Essential Nutrients 

1.2.1.1 Nitrogen 

1.2.1.2 Phosphorous 

1.2.1.3 Potassium 

1.2.1.4 Calcium 

1.2.1.5 Magnesium 

1.2.2 The Effect of Salinity on the Vegetative Growth of 
TomeJo 

1.3 Flower Development 

1.3.1 Introduction 

viii 

Page 

vi 

viii 

xii 

xiii 

xiv 

xv 

1 

3 

3 

4 

4 

4 

6 

6 

7 

9 

10 

11 

11 



ix 

1.3.2 Flower Formation 12 

1 .3.3 The Influence of Environment on Flower 
Formation 13 

1 .3.4 Pollen Production and Development 16 

1.4 Fruit Development 19 

1.4.1 Introduction 19 

1.4.2 Physical Changes in Developing Tomato Fruit 19 

1.4.3 Factors Affecting Fruit Growth 23 

1.4.4 Maturity and Ripening of Tomatoes 30 

1.4.4.1 Structure of Tomato Fruit 30 

1.4.4.2 Maturation and Ripening 32 

1.5 Quality of Tomatoes 36 

1.5.1. Introduction 36 

1.5.2 The Composition of Ripening Tomatoes 37 

1.5.3 Flavour as a Quality Attribute of Tomato 37 

1.5.4 Sugar as a Component of Flavour 39 

1.5.5 Organic Acids as a Component of Flavour 41 

1.5.6 Aromatic Volatiles 43 

1.5.7 Appearance as a Quality Attribute of Tomato 44 

1.5.8 Firmness and Shelf Life of Tomato Fruit 45 

CHAPTER 2. The Effects of High Conductivity Liquid Feeds on the 
Yield and Quality of Outdoor Grown Tomatoes 47 

2.1 Introduction 47 

2.2 Materials and Methods 48 

2.2.1 Plant Propagation and Transplanting 48 



X 

2.2.2 Land Preparation 49 

2.2.3 Base Fertilizer Application and Transplanting 49 

2.2.4 Treatments and Experimental Design 50 

2.2.5 Trickle Irrigation System 51 

2.2.6 Preparation of Liquid Feed 52 

2.2.7 Irrigation Schedule 54 

2.2.8 Conductivity Treatments 55 

2.2.9 Plant Training and Protection 55 

2.2.10 Harvesting and Grading 56 

2.2.11 Assessment of Fruit Quality 57 

2.2.11.1 Fruit Firmness 58 

2.2.11.2 Reducing Sugars 58 

2.2.11.3 Titratable Acids 58 

2.2.11.4 Total Solids 59 

2.2.12 Leaf Analysis 59 

2.2.13 Soil Conductivity and Percent Soluble Salts 59 

2.2.14 Statistical Analysis 60 

2.3 Results 61 

2.3.1 Nutrient Content of the Leaves 61 

2.3.2 Soil conductivity and Percent of Soluble Salts 62 

2.3.3 Fruit Quality Characteristics 64 

2.3.4 Total Number and Yield of Fruit 71 

2.3.5 Marketable Fruit 72 

2.3.5.1 Number and Yield of Marketable Fruits 72 

2.3.5.2 Distribution of Number and Yield of 
Marketable Fruit 73 

2.3.5.3 Size of Marketable Fruit 76 



2.3.5.4 Reject Fruit 

2.4 Discussion 

2.4.1 Nutrient Content of the Leaves 

2.4.1.1 Nitrogen 

2.4.1.2 Phosphorous 

2.4.1.3 Potassium 

2.4.1.4 Calcium 

2.4.1.5 Magnesium 

2.4.2 Conductivity of Soil Solution 

2.4.3 Fruit Quality Attributes 

2.4.3.1 Acidity 

2.4.3.2 Total Solids 

2.4.3.3 Fruit Firmness 

2.4.3.4 Total Soluble Solids 

2.4.4 Total Number and Yield of Fruit 

2.4.5 Marketable Fruit 

2.4.5.1 Size of Marketable Fruits 

2.4.5.2 Reject Fruit 

CHAPTER 3 SUMMARY 

REFERENCES 

PLATES 

APPENDICES 

xi 

77 

78 

78 

78 

80 

80 

82 

82 

83 

84 

84 

85 

87 

88 

89 

90 

90 

91 

92 

94 

107 

111 



xii 

LIST OF TABLES 

Page 

Table 1. MAF Soil Test and Target Levels 50 

Table 2. Standard Greenhouse Tomato Stock Solution and 
Resulting Liquid Feed 52 

Table 3. Determination of Stock Solution (1:100) dilution 
Required for 3 Conductivity Treatments 54 

Table 4. Nutrient Analysis of the Youngest Mature Leaf 30 
Days after Planting 61 

Table 5. Nutrient Analysis of the Youngest Mature Leaf 
Days after Planting 62 

Table 6. Percent Soluble Salts 63 

Table 7. Conductivity of Soil Solution ( mS cm-1l 64 

Table 8. Fruit Quality Attributes in Response to Treatments 65 

Table 9. Quality Attributes of Tomato During Harvest 65 

Table 10. Total Fruit Number and Weight of Fruit per Plant 
(Harvest 1-18) 71 

Table 11. Fruit Number per Plant (Harvest 1-19) 72 

Table 12. Marketable Number and Weight of Fruit per Plant 73 

Table 13. Numbe; of Marketable Fruit on the Main Stem 
per Plant 74 

Table 14. Weight of Marketable Fruit on the Lateral Stem 
(kg per plant) 74 

Table 15. Weight of Marketable Fruit on the Main Stem 
(kg per plant) 75 

Table 16. Weight of Marketable Fruit on the Lateral Stem 
(kg per plant) 75 

Table 17. Size of Marketable Fruits 
(New Zealand Fresh Tomato Industry) 76 

Table 18. Number and Weight (kg) of Reject Fruit per 
Plant 77 



xiii 

LIST OF FIGURES 

Page 
Figure 1. Relationship Between Dilution Rate 

and Conductivity 53 

Figure 2. Effect of Salinity on Titratable 
Acids During Harvest 67 

Figure 3. Effect of Salinity on Accumulated Total Solids 
by Weekly Harvest 68 

Figure 4. Effect of Salinity on Fruit Firmness by 
Weekly Harvest 69 

Figure 5. Effect of Salinity on the Percentage of Total 
Soluble Solids by Weekly Harvest 70 



LIST OF PLATES 

Plate 1. Grading Chart 

Plate 2. Set-up for Weighing the Fruit 

Plate 3. Tomato Root System 

xiv 

Page 

108 

109 

110 



LIST OF APPENDICES 

Appendix 1. Growing Media 

Appendix 2. The Otaki System of Tomato Fencing 

Appendix 3. Experimental Design 

Appendix 4. Soil Moisture Deficit 

Appendix 5. Spraying Programme 

Appendix 6. Formula for Determining the Acidity 
of the Fruit 

xv 

Page 

111 

112 

113 

114 

115 

116 



1 

GENERAL INTRODUCTION 

The tomato is a highly valued outdoor crop in New Zealand. It is grown 

commercially whenever environmental conditions permit an economic yield to be 

obtained. Consumers continue to use large amounts of this product, but 

increasingly there has been publicity which suggest that tomatoes are not what 

they used to be. This is so because plant breeders and producers in their 

attempt to produce high yields have, according to a widely held view, sacrificed 

fruit quality. 

Up until recently the important quality attributes of the tomato were perceived to 

include size, shape, colour and firmness of the fruit. At the present time however 

consumers are increasingly suggesting that fruit flavour should be added to this 

list. It is well established that the quality of tomato fruit can vary in response to 

both genetic and environmental factors. It is likely that tomato breeding programs 

for both greenhouse and outdoor tomatoes will now start to consider 

improvements in fruit flavour as an important goal. Research has established 

that there is a close relationship between acid and sugar levels in tomato fruit 

and fruit flavour. Recent developments with greenhouse tomatoes has shown 

that increases in titratable acidity and total soluble solids can be achieved by the 

use of high conductivity liquid feeds. These improvements in quality have been 

associated with some loss of yield. 



2 

Drip irrigation refers to the application of irrigation water and fertilizer nutrients 

through small emitters placed on or in the soil near the plants. One of the 

advantages of drip irrigation is its ability to conserve water and fertilizer compared 

with other irrigation and fertilizer systems. With drip irrigation water is not applied 

to plant foliage maintaining drier plants and reducing susceptibility to disease 

outbreak with an associated reduction in the need for fungicides. Drip irrigation 

has been widely used with field vegetable crops in the USA. 

The objective of the research discussed in this thesis was to use drip irrigation 

to examine the potential of using high conductivity liquid feeds to improve the 

flavour of field grown fenced tomatoes. Of particular interest was the likely trade 

off between fruit quality and yield. 



1.1 Introduction 

CHAPTER 1 

REVIEW OF LITERATURE 

3 

Production of tomatoes has dramatically increased due to the increasing 

popularity of the commodity both for fresh consumption and processing. Despite 

the large improvement in yield that has taken place over the years, fruit quality 

in terms of composition has received more lip-service than the actual research 

effort to improve it. 

Consumers are becomingly concerned about the quality of the fruit they buy. As 

we begin to understand more of the quality attributes that consumers demand 

of this product, there is a necessity to develop production technologies 

appropriate to meet this demand without sacrificing marketable yield. It is a 

general observation that an important quality problem with some cultivars is the 

lack of flavour. This may be alleviated by means of the production system used. 

Part of the tomatoes success as a crop is attributed to its ability to acclimate to 

different environments (Rick, 1978). There are numerous environmental factors 

that determine wether the tomato plant live up to its potential. According to Brice 

(1978), tomato plants require major elements and trace elements to maintain 

normal growth and development. 



4 

Adams (1986) and Stanley and Geraldson (1991) suggest that in orderto achieve 

high yields and good quality fruits, proper nutritional conditions must be 

maintained. Regardless of the system used in the application of nutrients, the 

primary concern must be to provide tomatoes with the nutrients they require at 

each stage of growth (Stanley and Geraldson, 1991 ). 

1.2 Plant Nutrition 

1.2.1 Responses of Tomato Plant to Essential Nutrients 

1.2.1.1 Nitrogen 

Nitrogen is readily absorbed by plants and easily leached from the soil. Winsor 

et al. (1967) reported that nitrogen fertilizer should be applied with care since 

excessive nitrogen is detrimental particularly during the reproductive stage. The 

response of tomatoes to nitrogen application, as with other plants, varies with 

the source (Adams, 1986), water availability, mode of application and how will 

the plant is supplied with other nutrients (Mengel and Kirkby, 1987). 

Pill and Lambeth (1977) reported that when tomato plants received NO3-N the 

fresh and dry weight of above ground parts increased comparably with NH4-N. 

The observation of Mengel and Kirkby (1987) regarding the response of various 

plants to NH4-N and NO3-N was that when plants received NH4-N, the uptake 

takes place best in a neutral medium, but was depressed as the pH fell. 



5 

Absorption of NO3-N on the other hand is more rapid at low pH. Uptake of 

nitrogen is also temperature dependent. The most important difference between 

NO3-N and NH4-N was that NH4-N is absorbed more readily at lower 

temperatures than NO3-N. It was further suggested that since photosynthesis in 

young tomato seedlings was low during winter it maybe safer to apply NO3-N 

than NH4-N. This is because plants with low carbohydrates often show toxicity 

when NH4-N is high. 

In the field fertilizer can be applied banded, broadcast or injected as in trickle 

irrigation. In order to stabilise nitrogen removal from soil be it as plant product, 

leaching or denitrification, it must be supplied in adequate amounts to the soil. 

During high rainfall or excessive irrigation nitrogen content around the roots is 

reduced particularly NO3-N, which does not react with the soil (Bar-Yosef and 

Sheikholslami, 1976) and NO3-N will then move with water below the root zone 

(Goldberg et al., 1971 ). 

The leaching problem with nitrogen can be alleviated by the introduction of trickle 

irrigation. According to Elfving (1982) following the application of the fertilizer 

through trickle irrigation roots of plants will have easy access to nitrogen. The 

emission ports are directed towards the base of the plant, and precise 

application of nitrogen in the plant rooting zone is possible (Stanley and 

Geraldson, 1991 ). By this means, nitrogen content in the soil at any one time will 

result from an equilibrium between addition by trickle irrigation and removal by 

plants plus any losses from leaching or denitrification. 



6 

1.2.1.2 Phosphorous 

Phosphorous concentration in soil solution is very dilute. It is used less by 

tomatoes than nitrogen and potassium, but at a steady rate throughout the life of 

the crop (Brice, 1978). When plants have high demand for phosphorous, the rate 

of absorption by the roots is high and the soil solution in the direct root vicinity 

is depleted of phosphorous (Olsen and Watanabe, 1970). Phosphorous in 

contrast to nitrogen is readily fixed in many soils (Kalkafi and Bar-Yosef, 1980). 

Thus, if the fertilizer is not mechanically worked deeply into the soil, most 

phosphorous will remain near the surface where availability will be limited. With 

frequent irrigation total phosphorous uptake was increased (Hedge and Srinivas, 

1990). This was enhanced by movement of phosphorous towards root by 

diffusion, however its availability depends on soil water status. When soils are 

deficient in phosphorous, tomatoes become dwarfed and spindly with purple veins 

and leaf stalks. This deficiency normally occurs when tomato plants are grown 

in soils with a high capacity to fix phosphorous (Adams, 1986; Brice, 1978). 

1.2.1.3 Potassium 

Of the macronutrients essential for growth and development of tomatoes, 

potassium is the most unusual since it has no direct contribution to the cellular 

structure of the plant (Adams, 1986). The function of potassium appears to be 

that of a regulator for many of the metabolic processes in cells including protein 

synthesis. 



7 

Potassium is more readily exhausted than many other nutrients. Brice (1978) 

estimated that tome.to plants over a season can utilize 680 kg of potassium per 

hectare twice as much as nitrogen. Potassium has considerable influence on fruit 

quality and yield (Adams and Grimmett, 1986). Winsor (1979) and Adams et al. 

(1978) showed that although low levels of potassium is sufficient for yield, higher 

levels have been shown to improve all aspects of fruit quality. Dry matter and 

titratable acid of the fruit generally increase with an increase in potassium level 

(Davies and Winsor, 1967). Winsor et al. (1961) reported that potassium 

improves fruit shape while Shafshak and Winsor (1964) showed that fruit firmness 

was also improved. 

Potassium deficiency is most likely to occur on heavy clay soils or on light sandy 

soils inadequately supplied with potassium (Adams, 1986). Symptoms exhibited 

by tomato plants grown in potassium deficient substrate include yellowing of the 

leaf margin, uneven ripening, hollowness, irregular shapes, softness and insipid 

flavours due to lack of acidity (Brice, 1978). 

1.2.1.4 Calcium 

The potential uptake of calcium is very much lower compared to potassium 

despite its concentration in the soil which is ten times higher than that of 

potassium (Mengel and Kirkby, 1987). The low potential uptake of calcium 

according to Ferguson et al. (unpublished) arise because calcium can be 

absorbed only by young roots in which the endodermis are still unsuberized. 



8 

Apart from this uptake mechanism, the presence of other cations which are easily 

absorb and translocated within the plant tend to depress the uptake of calcium 

(Mengel and Kirkby, 1987). This partly illustrates that although soils hold 

comparable amounts of calcium its concentration in the plant is still low due to 

its controlled uptake. Ferguson et al. (unpublished) recommended that levels of 

other cations should be kept comparably low but above deficiency levels if the 

site is known to give rise to plants with calcium deficiency problems. Maynard 

(1991) added that apart from cation restriction, calcium uptake can also be 

depressed by salinity of the soil solution, low temperature, dry soil and high 

humidity. Calcium uptake appear mainly to be a passive process. Calcium that 

is absorbed by the plant roots is distributed throughout the plant principally along 

with water. 

In tomatoes once calcium has been assimilated in the leaves, it can no longer be 

translocated to actively growing parts with low transpiration surface (Adams, 

1986). Calcium plays a critical role in maintaining cell membrane integrity. Since 

actively growing parts of the plant are deprived of their calcium requirement they 

are the first to exhibit calcium deficiency. Maynard (1991) reported that tomato 

plant deficient in calcium exhibit undeveloped leaves at the growing points, 

interveinal yellowing in young leaves and blossom end rot in the fruit (Adams, 

1986; Brice, 1978). 



9 

1.2.1.5 Magnesium 

Magnesium is more abundant in soils than potassium, but its uptake rate is 

comparably much slower than potassium. Magnesium transport is passive 

moving against the electrochemical gradient (Mengel and Kirkby, 1987). Adams 

(1986) clarified that in tomato plants magnesium acts as an activator for certain 

enzymic reactions. Potassium, NH4 and calcium may play a primary role in 

magnesium uptake. This competition can lead to magnesium deficiency in 

tomato plants. 

Research work reported by Brice (1978) show that the average magnesium 

uptake over a season is 290 kg ha-1. Although high levels of potassium often 

depress total magnesium uptake, increase potassium supply affects magnesium 

content of different plant organs to a varying extent. For example, increasing 

potassium supply reduced magnesium content of tomato leaves and roots 

respectively, but the magnesium content in fruit according to Viro as cited by 

Mengel and Kirkby (1987), can be increased by higher levels of potassium in the 

nutrient solution. Magnesium is very mobile in the phloem and can be 

translocated from older to younger leaves. Since developing fruits are highly 

dependent on the phloem for their mineral supply they are thus higher in 

potassium and magnesium. 

Magnesium inadequacy in tomatoes is usually due to the plants failure to 

assimilate magnesium from the soil (Brice, 1978). Tomato plants deficient in 

magnesium show interveinal yellowing on the lower leaves and gradually which 



10 

spreads to all foliage. The disorder is very prevalent when plants are carrying 

their heaviest fruit load. 

1.2.2 The Effect of Salinity on the Vegetative Growth of Tomato 

The development of salinity tolerance species according to Shannon et al. (1987) 

is an agronomic approach to the exploitation of large areas of saline soils and the 

efficient use of relatively abundant saline water supplies that currently have little 

agricultural value. 

As more and more land is brought into crop production through the development 

of irrigation, Jones (1986) has predicted the widening problem of salinity. Soils 

affected by salinity represent an important limitation to crop production particularly 

for crops that are sensitive. For tomato production, this does not pose a threat 

provided salinity levels do not exceed tolerable levels. 

Tomato plants are particularly sensitive to salinity at seedling the stage. 

Indications of stress in tomato were reported by Zerbi et al. (1991) as reductions 

in photosynthetic activity and leaf water potential which resulted later in reduced 

yield. Charbonneau et al. (1988) studied the effect of salinity of liquid feeds and 

they reported that raising the conductivity of the solution from 2 to 1 O mS cm-1 

decreased linearly the shoot dry weight by 30%, a clear demonstration that 

raising salinity reduced vegetative growth. 



11 

This finding confirmed the work of Papadopoulos and Rendig (1985) who used 

NaCl and CaCI to raise the salinity of the nutrient base solution. 

Dalton and Poss (1990) suggested that salinity tolerance is controlled not only 

by the inherent genetic characteristics of plant, but also by some yet to be 

determined processes in the plant. Tomato plants that were able to withstand 

salinity exhibited lower growth rates and had a slightly darker green colour than 

the less tolerant cultivars (Rush and Epstein, 1976). 

1.3 Flower Development 

1.3.1 Introduction 

One of the major events in the life of a tomato plant is the transition from 

vegetative (non-flowering) state to reproductive (flowering) state. The first signs 

of the transition from vegetative to reproductive state, which is termed flower 

initiation occur at the apical stem. Once flower initiation is started, particularly in 

indeterminate cultivars, it continues throughout the life of the plant. Flowers 

whose growth and development become arrested may senesce prematurely 

before flower opening can occur. This pre-mature loss is known as flower 

abortion. 



12 

1.3.2 Flower Formation 

The vegetative period of tomato seedling lasts for about 11-31 days depending 

on the light conditions after pricking out (Brice, 1978). Whenever the vegetative 

phase is reduced, Atherton and Harris (1986) predicted early fruit production, 

while extended vegetative growth allows the formation of more leaves preceding 

the inflorescence and then delay fruiting. Hurd and Cooper (1970) suggested 

monitoring of leaves as an indicator of flower initiation. They suggest that 3 

weeks after cotyledonary leaf expansion, most if not all tomato cultivars start to 

initiate flowers. This coincides with the third leaf reaching a length to just in 

excess of 10 mm, 

Inflorescence development in tomatoes require substantial amount of 

photoassimilate in excess of the amount required for growth. Hurd and Thornley 

(1974) reported that before tomato plants are set to initiate inflorescence, they 

have to initiate at least 6-8 leaves. This number of leaves is enough to intercept 

enough light needed for a sufficient production of photoassimilate for 

development of good quality flowers and fruits on the first truss. The hypothesis 

of Sachs and Hacket (1969) is in accord with the findings of Hurd and Thornley. 

According to this theory, the amount of photoassimilate available to the apex 

must reach a certain level before the transition can take place. 



13 

1.3.3 The Influence of Environment on Flower Formation 

The effects of environment can be both on flower initiation and subsequent flower 

development. Since flowering is determined by the appearance of visible flowers 

or buds, the data are sometimes insufficient to be sure which developmental 

stage is being affected by environmental factors. Environmental factors 

associated with fruit set and development in tomatoes were mostly identified 

under controlled environments, where such factors are subject to relatively close 

control. 

For most cultivars, the ideal day temperature for vegetative growth is about 18 

to 25°C (Hussey 1973). Temperatures below this range are damaging as it 

reduce vegetative growth more than flower development, whereas higher 

temperature favour vegetative growth at the expense of flowering. Studies of 

Abdul and Harris (1978) show that young leaves excised from plants grown at 

low temperature contain low levels of diffusible gibberellins that promoted an 

increase in number of flowers initiated in the first truss. Leaves excised from 

plants exposed to high temperature contain high levels of a gibberellic acid-like 

diffusible substance thus giving them more advantage for attracting assimilate. 

Following the exposure of plants to high temperatures, Dinar et al. (1983), 

suggested that leaves restricted the amount of photoassimilate exported to sink 

organs particularly apex due to high maintenance respiration. Mofo and La Malta 

(1986) while studying the relationship between flowering and pre-planting 



14 

temperature found that once plants were exposed to low day and night 

temperature treatments, the number of leaves preceding the inflorescence were 

significantly reduced along with vegetative growth. One important result from 

these studies shows that inflorescence was initiated at low temperatures 

because the apex was able to assimilate with young leaves as their growth is 

restricted due to low temperatures. Koning (1991) reviewed the relationships 

between flowering temperature and flowering and found that at 17°C and for 

every 2°C rise in temperature, flowering was advanced by 0.1 truss per week. 

High irradiance is necessary to produce photosynthates required for flowering. 

As light integral increases, the number of leaves before the inflorescence 

decrease as does the time of truss appearance (Kinet, 1977). It appears that 

since the number of days to flower initiation was reduced along with a reduced 

number of leaves, the inflorescence is placed in a more competitive position for 

attracting photoassimilate over the young expanding leaves. 

The number of flowers in the first inflorescence tend to increase as the light 

integral is increased. For example, when solar radiation levels were high, flower 

opening occurred about 40 days after cotyledonary expansion irrespective of total 

radiation received (Atherton and Harris, 1986). Initial reductions in light had a 

greater effect than the subsequent light reductions. Flower initiation and 

development according to Calvert (1969) is adversely affected more than 

vegetative growth whenever the carbohydrate supply is insufficient. These 

mechanisms clearly show that when photoassimilate is limiting, the plant 



15 

sustainsvegetative growth in preference to other sink organs by diversion of 

photoassimilate from leaves and away from the inflorescence. 

Some cultivars are regarded as qualitative short day plants (Kinet, 1977a). 

Experimental evidence suggests that at the same light integral an eight hour 

daylength reduced the number of subtended leaves and time to initiation of the 

inflorescence compared to plants exposed to sixteen hour daylength. 

There is no questicn that carbon dioxide enrichment increases yield primarily by 

increasing fruit set and the final size of the fruits. Additional carbon dioxide 

increases the carbohydrate status of the plant through an increase in net 

photosynthesis. Thus from the studies conducted by Hand (1968) it was reported 

that carbon dioxide enrichment increases the rate of leaf initiation slightly and 

decreased the time to flower initiation. The effect of carbon dioxide is greater 

when there is an increase in light integral. 

Reproductive growth and fruitfulness of tomatoes relies on the correct balance 

between carbohydrate and fertilizer supply. Tomato plants exhibit growth 

retardation and flower abortion due to inorganic nutrient deficiency in the growing 

medium. When the macro-elements are in short supply, tomatoes tend to slow 

down flower induction, an indication that the plant is under nutrient stress. 

The size of the first inflorescence is affected by the supply of inorganic nutrients 

in the rooting medium when it was initiated. 



16 

Of the major elements supplied nitrogen is the most important. When its supply 

is limiting vegetative growth and flower induction is severely affected . 

Earliest reported effect of nitrogen on flower induction was that of Wittwer and 

Teubner (1957) who found that the number of flowers in the first inflorescence 

can be increased by increasing supply of nitrogen. The most profound effect was 

apparent when plants were exposed to 10-13°C when branching of inflorescence 

was more prevalent. Low supply of nitrogen in the growing medium increases 

the incidence of flower abortion. 

Fisher (1969) reported that low levels of nitrogen in the solution decreased flower 

number. The same obseNation were reported by Adams et al. (1973) when 

growing single truss plants. 

1.3.4 Pollen Production and Development 

When the daytime temperature is at 20°c and under high light conditions, Picken 

(1984) obseNed that sexual reproduction in mother cells took place nine days 

before fruit set. In most instances the quality of viable pollen formed is the most 

important criteria in pollen production. Between 5-7 days before anthesis, 

damage caused by high temperature on pollen grain is even more severe than 

on the ovules because at this stage fruit set can be improved only by the 

application of untreated pollen. 



17 

Tomatoes are generally self pollinated (Ho and Hewitt, 1986). Mature pollen is 

ready for transfer at the time of anthesis while the stigma is receptive about two 

days previously and remains up to four days or more (Ho and Hewitt, 1986). 

Adherence of the pollen grains into the stigma is vital to allow germination to take 

place. The adherence of pollen grains into the stigma is greatly reduced when 

the relative humidity is 70% or if the temperature is outside the range of 17 to 

24°C (van Ravestijn, 1970 cited by Ho and Hewitt, 1986). Successful transfer of 

pollen grains to the stigma is also dependent on the length of the style and the 

nearness of the stigma to the anther cone for self pollination (Rick and 

Dempsey, 1969). ,, 

Rick and Dempsey (1969) observed that tomato cultivar whose stigma is within 

the anther cone set fruit easily whereas in cultivars with exerted stigma or 

elongated style, pollination and fruit set are seriously affected. The length of the 

style determines the degree of insertion or exsertion of the stigma and is 

generally influenced by external growing conditions. Hannah and Hernandez 

(1984) studied the response of six cultivars grown in summer and spring 

conditions and found that high temperature influence exsertion while low 

temperature induce insertion. The observation of Munoz and Cuartero (1991) 

on the effects of temperature on stigma position is in agreement with the 

previous report. 

Fertilization has been first observed 18 hours after the adherence of pollen 

grains to the stigma and most ovules would be fertilized within 30 hours. 



18 

The extent of fertilization is dependent upon the number of viable pollen grains 

reaching the stigma, environment, physiological factors and the process of 

pollination and fertilization (Picken, 1984). 

Pollen germination is temperature dependent (Ho and Hewitt 1986). The degree 

of germination is greatly reduced when the temperature is below 5°C or when it 

exceeds 37°C. Tomato cultivars grown in the field exhibit some heat sterility 

specially during summer and this accounts for a reduction of yield. The most 

commonly accepted explanation to this has been that it was due to the abortion 

of pollen grains at extreme temperatures. 

Shelby et al. (1978) cited the study of Schaibe and reported that when night 

temperature reaches 32°C tomato fruit set is limited. In the same year Kuo et 

a/,(1979) found that most failures in tomato fruit set was due to immediate 

exposure of the flowers to high temperatures, but observed that if such exposure 

was done 5 to 8 deys after anthesis the flowers tend to tolerate the temperature 

level. 

Viability of pollen grains vary with different times of the day. When the stigma 

of the male sterile plants were hand pollinated with viable pollen it took 6 hours 

to reach the stylar end, but when pollinated early in the morning it took 12 hours 

(Picken, 1984). The growth rate of the pollen tube increases when the 

temperature is between 1 o0c and 35°C and decreases if the temperature is 

outside this range. 



19 

1.4 Fruit Development 

1.4.1 Introduction 

Fruit set is a crucial factor that influences yield. Normal fruit growth requires two 

important processes namely, pollination of the flower, and the steady supply of 

assimilates. Undecstanding the mechanisms in these processes will enable us 

to manipulate and improve yield as well as the sensory qualities of the fruit 

(Archbold et al., 1982). 

Fruit number and individual fruit weight are two important components of yield. 

Together with sensory attributes like size and shape these are influenced by 

the number of seeds produced, based on the quality of viable pollen that 

germinates in the stigma (Picken, 1984). 

1.4.2 Physical Changes in Developing Tomato Fruit 

Fruit growth is part of an integrated development of the plant. Fruit growth is 

determined by the interaction between growing conditions and morphological 

characters as well as physiological activities of the whole plant. It has long been 

recognized that the improvement of the fruit is dependent upon understanding 

the factors controlHng assimilate production in the leaves and the enzymatic 

activities that deter,·nine sink strength. The key to understanding the factors that 



20 

regulate fruit growth is to identify how the morphological factors respond to 

environment and how the metabolic processes inside the fruit interact with the 

rest of the plant. 

Fruits are reversible storage sinks as the imported assimilates are either used 

for growth or stored as reserves (Ho, 1988). It is indeed important to understand 

how the supply and the competition for assimilates for each fruit is regulated. 

Fruit yield in terms of dry matter production is related to assimilate supply and 

hence to the radiation levels intercepted by the crop. This relation however does 

not imply that .any increase in fruit yield is entirely determined by the 

improvement of photosynthesis. Fruit yield can also be improved by changing the 

dry matter partitioning and by manipulating the factors that determine the sink 

strength of the fruit (Gilford and Evans, 1981; Ho, 1988). Before fertilization, the 

dry matter accounts for 17% of the ovary weight. As the fruit grow, the dry 

matter content of the ovary as a percentage of fresh weight declines as the 

amount of water accumulated increases (Ho and Hewitt, 1986). The rate of dry 

matter accumulated declines to less than 10% after 1 0 days and 5% to 7% by 

day 20 and remains at this level until maturity. 

The rate of growth and development of tomato fruit is divided into 3 periods. 

First, there is a slow growth for 2 to 3 weeks when the gain in weight is less than 

10% of the final weight (Ho and Hewett, 1986). The growth of the ovary ceases 

at anthesis and then resumes after fertilization. 



21 

Two days after pollination the growth of the ovary is sustained by the importation 

of assimilates from the nearby leaves. Thus the rate of dry matter accumulation 

in fruits of the same potential size will relate to the concurrent photosynthesis in 

the leaves. According to Ho et al. (1983), fruits accumulate as much as 30 to 50 

mg of dry matter after two weeks of growth. It was subsequently observed that 

from twenty to twenty five days after anthesis, there was a period of rapid growth. 

While the growth rate increases during this period, the daily import rate of carbon 

diminish from 140 mg to approximately one half as the fruit increases from 20% 

to 90% of its carbop content. The decrease in carbon accumulated by the fruit 

is due to the formation of an abscission layer between the calyx and the fruit 

(McCollum and Skok as cited by Ho and Hewitt, 1986). 

When the fruit is mature green, Ho and Hewitt (1986) observed that fruits 

undergo slow growth marked by little addition in weight for almost 2 weeks. 

However intensive metabolic changes occur. The slow growth was the result of 

initial cell division and enlargement, while the rapid growth was entirely due to cell 

enlargement. 

Enlargement of pericarp is positively related to the auxin activity in the fruit 

(Asahira and Hosoki, 1977), while the shape of the fruit results from the 

differential growth of the ovary at the polar and equatorial dimension before 

anthesis. Locular cavities which vary from two and above occur as a gap in the 

pericarp. The locules contain seeds located in the homogenous gelatinous mass 

of thin walled parenchyma like cells that fill the !ocular cavities (Varga and 



22 

Bruisnma, 1986). These tissues appear very early and are thought to be formed 

by an outward growth from the placenta surrounding the seeds. 

The number of locules in the ovary is dependent on the flower position within the 

truss. Ovaries of the first flower on the first truss may have more locules than 

subsequent fruit. If this is the case, then the first fruit is larger than the rest, 

particularly those at the distal section of the truss. 

Since fruit size is of economic significance, increasing the locule number will 

enhance the size of the fruit. Introduction of genes to increase the locule number 

have paved the way to increasing the size of the fruit. Aside from the genes, 

Sawhney et al. (1971) confirmed that by applying gibberellic acid to pre-floral 

plants stimulated an increase in the number of carpels and locules in the ovary. 

In addition to these observations, the style of the treated flowers were thicker, 

contained more vascular bundles and there was an increase in ovary size. 

Reducing sugars at the onset of fruit growth account for 0.1 % of the ovary fresh 

weight and there was a gradual increase to 1.2% within 2 weeks and 3.5% 

thereafter until ripening occurred (Ho and Hewitt, 1986). Sucrose accounts for 

1 % of the dry matter or in a range of 0.1 to 0.2% of the fresh weight. Although 

lower in percentage, it is important for fruit growth (Walker and Ho, 1979). After 

pollination, reducing sugars and starch increase sharply, but sucrose reduces to 

1 % to 0.2% of the' fresh fruit weight within· 8 days. Although sucrose is the 

principal sugar imported by the fruit, its content remain low throughout. 



23 

According to Ho et al. (1983), the highest dry matter gain by fruits daily is 370 mg 

per day in the proximal fruit while dry matter increment in the distal fruit is 

approximately 170 mg. The major or principal part of the fruit receiving more 

starch per fresh weight are the locular tissues and the placental tissues. 

Starch which is about 1 % of the dry matter when the fruit is mature green, starts 

to breakdown upon reaching maximum growth (Ho et al., 1983). This 

concentration was further redu.ced to approximately 0.03 % of the fresh fruit 

weight at the time of ripening (Hobson, 1967). The breakdown of starch is 

associated with the accumulation of hexoses hence a correlation exists between 

the starch content of a mature green fruit and the reducing sugars of ripe fruits 

(Dinar and Stevens, 1971 ). 

The concentration of organic acids expressed as percentage of the fruit fresh 

weight was reported by Ho and Hewitt (1986) to increase during fruit 

development. This concentration varies according to fruit section, thus locules 

is more acid compared to pericarp wall and placenta. During early growth malic 

acid is predominant (13 %), whereas citric acid account for 25 % of the total 

acidity. 

1.4.3 Factors Affecting Fruit Growth 

Tomato is a high yielding crop with fruits representing a large fraction of the total 

dry matter of the plant (Ho and Hewitt, 1986). 



24 

The reason for such a high proportion of dry matter allocated to fruit production 

is the high demand for sugars by the growing fruit. Developing fruit should be 

able to import high levels of sucrose from the leaves in order that at ripening, the 

fruit will contain high sugar and organic acids such that both the taste and texture 

of the fruit will be satisfactory. 

Tomato plants has a 2/5 phyllotaxy (Russell and Morris, 1983). Ho and Hewitt 

(1986) indicated that once the first inflorescence develops on one side of the 

plant, all succeeding trusses are on the same side of the stem with often 3 leaves 

in between trusses. The first two leaves below each truss are at angle 90° on 

either side of the truss, while the first leaf above the truss is on the opposite side. 

The assimilate supplied to the truss at flowering comes from the subtended 

leaves below the truss and not the leaves above the truss. At fruit initiation 

however, the assimilates are supplied from the leaves below the truss and the 

leaves above the truss (Ho and Hewitt, 1986). 

Tomato plants have a well structured system for distribution of assimilates and 

minerals to the various growing regions. The pattern of assimilate allocation to 

respective sinks is effective due to the arrangement of their vascular system 

(Russel and Morris, 1983; Yoshihiro et al., 1988). There are two main conducting 

tissues that sustains the growth of the fruit. The phloem, primarily conveys water 

and sugars from the leaves, while the xylem carries water and salts from the 

roots (Ho and Grimbly, 1990). In the dark, both phloem and xylem sustains the 

growth of the fruit, but higher growth rate in the daytime is mainly the result of an 



25 

increase in phloem flow bringing in sugar to the fruit. 

Most of the dry matter accumulated in the fruit is derived from assimilates 

imported from the leaves, thus fruit growth is mainly determined by the import 

rate of assimilates. Once carbon is fixed in a mature leaf, 20 to 30% can be 

exported to the developing fruits within 2 hours and approximately up to 45-50% 

within 2 days. The principal labile assimilate exported is in the form of sucrose 

making up 90% of the assimilate (Ho and Hewitt, 1986). 

At any one time when the supply of assimilate is limited, the fruit is sustained by 

both assimilates from the leaves and that remobilized from the reserves. 

Although the developing fruit is sustained by the leaves below the truss, 

transitory patterns occur depending upon the growth conditions of the fruit within 

the truss. Studies conducted by Bonemain according to Ho and Hewitt (1986) 

showed that at the peak of fruit growth large amounts of assimilate is required 

to sustain the needs of the developing fruits. The additional assimilate is 

supplied by re-mobilization of the carbon reserved in the roots and this can be 

re-exported within 3 hours in the form of amino or organic acids. 

The degree of competition for assimilate between vegetative and reproductive 

organs depend on their spatial and temporal relationships. In tomatoes, 

competition for assimilates between reproductive and vegetative organs is very 

localized, that is for every truss there are 3-5 leaves that act as source for 

assimilates (Ho and Hewitt, 1986). 



26 

As the developing fruits are stronger than flowers and vegetative organs, the 

competition for assimilates by a fruit is mainly with adjacent fruits within a truss 

as they derive their assimilates from the same group of leaves. The mechanisms 

involved in the regulation of competition between fruit is at present not fully 

understood. Ho (1984) elaborated that fruit growth may be determined by its 

inherent capacity to attract assimilate and its ability to compete with other fruits 

for assimilates. Most studies conducted to determine the strength of the fruit to 

attract assimilates involve sink size and activity as regulatory factors. 

Cell numbers contained in the fruit is at present considered a good measure of 

potential sink size. As the whole fruit mass is determined by cell number, cell 

size and cell content, while the final volume of the fruit is determined by the 

extent of cell enlargement (Coombe, 1976). 

Factors determining cell number in fruits have not been studied seriously. Ho 

(1988) stated that in tomato pericarp, the cell number appears to be associated 

with cambial activity of the vascular bundles . Although most cells of a fruit are 

derived from cell division following pollination (Mapelli et al., 1978), the difference 

in cell number of a fruit at various positions in the same truss already exists in 

the pre-anthesis of the ovary. The duration of cell division after anthesis varies 

from less than 2 weeks in tomatoes. 

Sucrose has been found directly or indirectly to be the predominant mobile 

assimilate in tomatoes (Walker and Ho, 1979). 



27 

At ripening, hexose account for about half of the fruit dry weight hence the 

hydrolysis of sucrose and subsequent storage of hexose may be important 

factors in regulating the import rate of carbon (Walker et al., 1978; Ho, 1988). 

If the partitioning of assimilates is motivated by the metabolic activities within the 

fruit, then the sink activity is a more primary determinant of sink strength than 

sink size. The strength of the developing fruit to attract assimilate has been 

thought to be the product of its dry weight. 

Winsor et al. (1967) studied the effect of light and carbon dioxide on fruit growth 

and found that al'chough the addition of carbon dioxide increased yield by 

increasing the number and weight of the fruit, the chemical composition of the 

fruit was not improved. The most accepted explanation why fruit composition 

was not improved, despite carbon dioxide enrichment, was that according to Ho 

and Grimbly (1990), although the number and size of the fruit was boosted as a 

result of carbon dioxide enrichment, the amount of assimilate imported by the fruit 

was accompanied by a similar amount of water, thus fruit weight is increased 

rather than the dry matter content. 

Both size and total soluble solid content of the fruit are influenced by the amount 

of light absorbed by the leaves. If light level are low during early growth the 

proportion of hollow fruits in the first truss is 80-100%, while dry matter content 

of the early yield is low. When the solar radiation is high both dry matter and 

sugar is high. This was demonstrated by Ho and Grimbly (1990), when they 

compared tomatoes imported from tropical countries with that produced in 



28 

Europe. Ho and Grimbly (1990) confirmed the previous observation that the 

amount of sugars imported by the fruit as a result of carbon dioxide enrichment 

is accompanied by the similar amount of water taken up by the fruit. They further 

explained why fruit weight increased rather than boosting the dry matter content 

of the fruit. The effect of light on the dry matter content of the fruit is different 

from the effect of carbon dioxide. Increases in light levels is accompanied by 

increases in temperature causing slight water stress. The fruit in return benefits 

from water stress by importing more sugars as the result of increased 

photosynthesis. High amount of light absorbed, slight water stress and a large 

leaf area are possible effective ways in increasing the sugar content of fruit. 

An efficient way of improving the quality of the fruit is the use of saline media 

and using the potential tolerance of tomato to salinity. As discussed by Shannon 

et al. (1987), the continued breeding of tomatoes to tolerate salinity has become 

an agronomic tool in the exploitation of saline soil not only in the field but also in 

controlled environment with considerable improvement in quality. Mizrahi et al. 

(1988) concluded that among the environmental factors responsible for the 

improvement of fruit quality, soil water availability and quality can readily be 

controlled and manipulated to increase the soluble sugar and acid concentration, 

thereby improving the quality of the fruit. With an increasing awareness of the 

effect of salinity on fruit quality, the search for materials to increase the electrical 

conductivity of the. solution without prejudicing the growth of the plant should 

have priority. In the NFT system several experiments have been conducted 

using different salt combinations to raise the conductivity of the solution. 



29 

Shalhevet and Varon (1973) added NaCl to the base nutrient solution and were 

able to increase the soluble solid content of the fruit by 24%. 

At high salinity both the uptake of water by the plant and the subsequent 

accumulation of water by the fruit is severely reduced, therefore the promoting 

effect of salinity is not on fruit density, but on the percent of fruit dry matter and 

sugar concentration in the fruit juice. This observation was confirmed by the 

results obtained by Ehret and Ho (1986), when they observed the dry matter of 

the fruits from salinized plants to increase ,as the conductivity of the solution 

increased. During rapid growth, Ehret and Ho (1986) observed that a high 

proportion of dry matter was stored in the fruit in the form of starch rather than 

sugars. The advantage of accumulating carbohydrates in fruits in the form of 

starch rather than hexoses according to Mitchell et al. (1991) is that it ensures 

continued sink activity therefore the accumulation of starch is maintained at a 

reduced tissue water level. These studies clearly demonstrate that when the 

assimilate supply is not limiting the amount of assimilate being imported by a fruit 

is not at all affectec;I by the water relations in,the plant. Although size of the fruit 

is reduced (Ho and Grimbly, 1990) the fruit have a higher percentage of dry 

matter. If for instance the purchase of the produce is based on the total solid 

content there would be no economic loss. 

When sugars are not limiting, fruit growth is regulated by temperature and water 

supply. Restricted watering and high salinity can be used to adjust fruit number, 

fruit size and improve taste. The effect of such reduction is not to reduce 



30 

phloem sap supply, but to increase the concentration of the sap without a 

reduction in the usual amount of sugar being imported by the fruit. Although less 

water is accumulated, the dry matter accumulated increase with high sugar 

concentration in the fruit. 

The effect of macro and micro elements has been discussed by Uexcull (1979). 

Adequate nitrogen improves fruit quality, while excessive application tend to 

decrease the size of the fruit, keeping quality, colour and taste. Phosphorous on 

the other hand in combination with potassium improves peel and pulp coloration, 

taste, firmness, vitamin C content and hastens maturity. Potassium tends to 

increase fruit size and plays a key role in the process of fruit pigmentation. It 

also influence acid metabolism. Inadequacy of calcium in the growing media will 

result to a number of physiological disorders.while magnesium deficiency can be 

induced by high rates of potassium or ammonium nitrogen application. 

1.4.4 Maturity and Ripening of Tomato 

1.4.4.1 Structure of Tomato Fruit 

Davies and Hobson (1981 ), botanically classified tomato fruit as a berry since the 

seeds are formed within the fleshy mesocarp. Tomato fruit is composed of flesh 

(pericarp wall, skin and pulp), placenta and !ocular tissue including seeds. 

Generally, less than a third of the fruit fresh ·weight is made up of pulp (Ho and 

Hewitt, 1986). 



31 

The skin is made up of 4 to 5 layers of cell under a thin cuticle. The epidermal 

layer is heavily cutinized on the surface. The epidermis is covered by a thin 

cuticle that thickens as the fruit matures ( Varga and Bruinsma, 1986 ). The cutin 

may surround the epidermal walls below and between the first layer of 

collenchyma. The importance of cutin is enhanced resistance of the fruit to 

cracking during ripening. This is very important particularly when tomatoes are 

grown purposely for processing and mechanically harvested and transported for 

long distances (Voisey et al., 1970). 

Vascular strands radiate from the stem end of the fruit to the pericarp down to the 

columella and to the blossom end. Cross connection in the pericarp are more 

common in the distal half of the fruit. A major vascular bundle, the centre line of 

each carpel, is developed extending from the stem scar to the blossom end of the 

fruit (Ho and Hewitt, 1986). In green fruits, the epidermal cells tend to have less 

starch than the inner parenchymatous cells. Most of the cell division in the 

pericarp takes place during the first week after anthesis, further division occur 

during the second week (Asahira et al., 1965 cited by Ho and Hewitt 1986). The 

number of cell layers increase from 8 to 1 O during this period however cell 

development was observed throughout fruit development. 

In mature fruits, the placental tissue is firm, but as it approaches maturity, the 

walls of these parenchymatous cells become thin and wavy and contain large but 

diminishing numbers of starch grains (Grierson and Kader, 1986). The 

appearance of jelly like material in the !ocular cavity provides an excellent 



32 

criterion whereby fruit may be designated mature green. The placental tissue at 

incipient ripening appears pink in colour. Two major groups of pigment in tomato 

fruits are chlorophyll and carotenoid. Prior to ripening chloroplasts lose starch 

and chlorophyll from the grana, followed by the production of osmophilic globules 

and the formation of lycopene within the swollen granum compartment. 

1.4.4.2 Maturation and Ripening 

The fruit of tomato requires approximately 40-60 days from flowering to full 

ripeness. After the initial phase of slow growth, Rick (1978) observed that the 

fruit undergo major increase up to full size in about half of the ripening period. As 

the fruit matures, cells in the pericarp become very large, thin walled and the 

parenchymatous cells around the seeds are reduced to semi-liquid immediately 

prior to ripening (Ho and Hewitt, 1986). The starch content reaches a peak 

halfway through development, when it makes up about 20% of the dry matter. 

This figure falls to 1 % at the mature green stage and is followed by a declining 

growth rate during which maturation and ripening usually occur. During this 

period, the fruit (Varga and Bruinsma, 1986) stores large amounts of reserve 

materials accumulated either through synthesis of sugars or elaborated in the 

nearby source leaves. 

Early ripening is marked by the completion of starch hydrolysis at which point 

reducing sugars are present in maximum concentration. At almost the same time 

malic acid, which was initially an important organic acid decreased gradually after 



33 

fruit maturity and is replaced by citric acid. The turnover in acid concentration 

in favour of citric acid causes the ratio of malate to citrate acid to fall during the 

later stages of maturity. Hobson and Harman (1986) elaborated that at maturity, 

the sugar content in the fruit, in particular reducing sugars, tends to be more 

concentrated in the !ocular walls while acids are more concentrated in the locular 

cavities. An increase in moisture content was also observed in the fruit, which 

accounts for 90-95% of fresh weight as the fruit develops. 

Aside from compositional changes, a series of structural changes are known to 

occur. Following a decline in growth rate, Bathgate et al. (1985) noticed gradual 

structural changes including membrane disintegration, chlorophyll breakdown and 

starch disappearance. Gradual chlorophyll degradation at this stage results in the 

whitening of the fruit which serves as a useful determinant of ripening. The 

following week is marked by destruction of the remaining chlorophyll when Harris 

and Spurr (1969) observed the transformation from chloroplast to chromoplast. 

During this transition, there was an increase in carotenoid content and synthesis 

of lycopene in the cytoplasm. Grierson (1987) noted that the mechanism of 

change was structured so that it took place at the same time that other ripening 

processes such as cell wall degradation, tissue softening and accumulation of 

sugars and organic acids were occurring. 

Ripening of tomato fruit involves a number of chemical and physical changes 

which convert the fruit from a relatively inedible state to one of optimal quality 

(Babitt et al., 1973). It is also a complex developmental process involving 



34 

changes in the biochemistry, physiology and gene expression of the fruit and an 

active process characterized by changes in all cellular compartments as well 

(Smith et al., 1989). It has been suggested by Saccher (1973) that the loss of 

cell membrane integrity, removal of permeability barrier and increase in free 

space serve as major factors in ripening and senescence. One of the early 

events that heralds the onset of ripening is the beginning of the respiratory 

climacteric, the rise in breakdown of proliferated cells that surround the seeds in 

the locules (Rabinowitch et al. 1975), the partial solubilization of the cell wall 

components leading to softening of the texture (Speirs and Brady, 1991 ), 

alterations in metabolism and composition of all major cell compartments 

(Grierson, 1987) and progressive changes in colour, texture, flavour and aroma 

in each tissue (Brecht, 1987). All these changes are highly synchronized 

appearing in close succession in a variety of distinct processes during the 

relatively short period which fruit ripens. 

The mechanisms by which fruit ripening changes are initiated and synchronized 

remains largely unknown. It therefore seems appropriate to look into factors that 

triggers the initiation and coordination of these changes. 

Essential to the initiation of ripening is the resistance of the fruit tissues to the 

effects of hormones that would trigger metabolic changes within the cells. 

Resistance of tissues to ripening hormones is a feature of most unripe tissues 

(Hobson and Harman, 1986). Once their resistance has been overcome by 

ripening hormones their evolution gradually rise from a low basal level. 



35 

The rate at which tissue sensitivity towards the ripening hormone occur 

determines the onset of ripening. 

One important and much studied process occurring during fruit ripening is 

softening. This involves changes in the structure and solubility of the fruit cell 

wall. The processes involved in fruit ripening has been extensively studied. The 

main issue under investigation here is the occurrence of ripening enzymes that 

eventually lead to metabolic degradation of fruit cells. Previous efforts to 

determine the enzyme that initiated ripening was made by Sacher (1973). 

Accordingly, there are numerous enzymes that have been shown to change their 

activities as the fruit ripens, and some of these show clear physiological 

relevance. For example, when Brecht (1985) measured the concentration of 

various enzymes in tomato fruit tissues, he found that during maturation the 

concentration of ACC increased in the locule tissue of green fruit coincident with 

gel formation. Brecht (1987) clarified that !ocular tissue was derived from the 

placenta of the fruit then overgrowing the seeds, which later on fill the locules, but 

not fusing with either the seeds or pericarp. At maturity, the cell walls become 

progressively thin and fragile eventually rupturing to produce the typical liquid jelly 

like consistency of mature ripe fruit. The activity of ACC synthase is not only 
' 

centred on the !ocular tissues but is spread out to nearby tissues like columella 

and placenta, whe(e synthase begins to increase at the mature green stage 

(Brecht, 1985). Similar increases also occur on radial and outer pericarp 

following the breaker stage. 



36 

ACC and ACC synthase continue to increase in columella and pericarp tissues 

beyond the breaker stage while levelling off (ACC) or falling (ACC synthase) in 

the gel as the tissue is degraded. The expansion and separation of cells and the 

cell wall fragments released at this stage, may act as elicitors of ethylene 

production (Brecht, 1985). The locular contents of tomatoes contributed 20% to 

the total fresh weight of the fruit thus a small increase in ethylene production 

observed in the whole fruit at the mature green stage probably represent a 

significant increase in the locule tissues rate of ethylene production. The 

relationship between ethylene production rate and maturity stage is a good 

index to determine physiological maturity of the fruit. 

1.5 Quality of Tomatoes 

1.5.1 Introduction 

Tomato quality has received attention only after the improvement of yield has 

been achieved. Consumer preference for fresh tomatoes is no longer limited 

to how they appear, but they are also demanding quality attributes based on 

flavour and nutritional value. It is generally accepted that ripe tomatoes 

purchased in supermarkets nowadays lack the desired aroma and flavour that 

there used to be when fruits were vine ripened. 

U.S.D.A. legislation regarding product information requires the inclusion of 

nutritional value of the product. This move will change the purchasing attitude 



37 

of consumers as they can compare product composition. The impact will not 

end where the product is being sold, instead growers will be obliged to do their 

part by changing their production practices so that their product will be 

competitive on the market. 

1.5.2 The Composition of Ripening Tomatoes 

Tomato fruits ripening either on or off the vine show compositional changes. It 

is at maturity that the ultimate quality of the fruit can be judged based on the 

perception of consumers. 

Tomato fruits during ripening contain a wide range of compounds and show 

considerable variation in composition and structure. The presence of many 

compounds that constitute the flavour of the fruit is the result of interactions with 

season, nutrition, environmental and physiological status of the fruit. 

The composition of present day tomato varieties is the result of combined efforts 

of research work to determine the factors that comprise fruit flavour in particular 

sugar, acid, and volatile compounds. 

1.5.3 Flavour as a Quality Attribute of Tomato 

Flavour is one of the most important constituents of quality, but at present has 

little effect on the initial sale of the product due to our failure to identify its 



38 

components. Tomato fruit are sensed differently by different individual and often 

impressions are affected by other non-flavour quality attributes. The unique 

flavour of tomato is a composite of taste smell and touch or mouth feel (Bezar, 

1989) and is a product of sugars, acids and aromatic volatiles contributing to 60 

% of the dry matter Hobson (1988). If the proportion of sugar in the fruit is low, 

the consumer will react to their sharp and biting taste, but if the fruit acid is low 

the unbalanced sweetness can be disturbing to the taste. Weight for weight 

acids affects the taste more than the sugars. Of the sugars that are used to 

balance acidity fructose has more sweetening power than glucose due to its 

higher concentration. 

Volatile compounds are not only important to aroma, but also to the overall 

flavour of tomatoes. Frenkel and Jen (1989), reported research work and 

concluded that although several hundred aromatic volatiles have been 

catalogued, there are still new compounds being discovered and added to the 

existing ones as research for other volatile compounds continue. Only a limited 

number of these are important to the aroma of the tomato fruit. Improving the 

sugar and acid ratio of the fruit requires effective combination of factors that 

influence the chemical composition of the fruit. Studies conducted by Ehret and 

Ho (1986) and Mizrahi et al. (1988) revealed that among the environmental 

factors that influence the quality of the fruit, nutrient and water availability and 

quality can be readily controlled and manipulated to increase the total soluble 

solids and acid c9ncentration. Mizrahi (1982) reported that increasing the 

concentration of the liquid feed increases the total soluble solids and acid of the 



39 

fruit. By imposing a range of salinity regimes, water uptake is regulated thus 

increasing the concentration of mineral ions in the fruit. The concentration of 

cations in the fruit varies with the kind of salts used to raise the conductivity of 

the nutrient base solution. Thus, when Ehret' and Ho (1986) imposed a range of 

salinity using potassium nitrate or calcium nitrate, potassium becomes the 

predominant cation in the fruit. 

An important factor in understanding the determinants of flavour is to know how 

to balance the acid and sugar content of the fruit. Bezar (1989), pointed out that 

fruit walls contain at least 20 % more sugar than the juice around the seeds, 

while the juice contain more acid than the pulpy part of the fruit. Hobson (1988) 

elaborated that if consumers wanted to derive a biting taste they should choose 

those fruits with bigger locular contents in contrast to pulpy fruits which gives a 

sweeter taste. 

1.5.4 Sugar as a Component of Flavour 

After water, sugars form the next most important constituent of the tomato fruit 

contributing almost 50% of the total dry matter of the fruit of commercially grown 

varieties (Winsor, 1966). Ripe fruit contain free sugars in the form of reducing 

sugars consisting of glucose and fructose in approximately equal amounts, but 

usually with a preponderance of fructose at late stage of ripeness (de Bruyn et 

a/., 1971; Davies and Hobson, 1981 ). On equal weight basis fructose is sweeter 

than glucose. 



40 

Hobson and Kilby (1985) and Baldwin et al., (1991) indicated that tomato fruit 

of normal size contain very little sucrose. Initially, Davies and Kempton (1975) 

reported that as the fruit develops there is a progressive increase in both glucose 

and fructose concentration and then they show a dramatic increase during the 

stage of cell enlargement where the ratio of glucose to fructose decreases 

rapidly. The pronounce rise in sugar concentration in the fruit coincides with the 

first appearance of yellow pigment in the walls accompanied by changes 

occurring in the whole fruit, !ocular juices and pericarp. 

Environmental and production practices greatly influence the sugar concentration 

of tomato fruits. Davies and Hobson (1981) pointed out that of the known 

environmental factors affecting the composition of the fruit it is probable light level 

has the most profound effect on sugar concentration. Thus seasonal trends in 

sugar levels reflect differences in the intensity and duration of light. Growers 

have limited opportunity to manipulate the sugar content of the fruit except for 

morphological modifications to improve light interception and agronomic practices 

to maintain the vigour of the plants and to increase the rate of photosynthetic 

production. Since fruits of most typical tomato cultivars contain 95% water the 

dry matter therefore constitute a very small fraction of the fruit. Ho and Grimbly 

(1990) estimated that the dry matter of the fruit comprises 8% minerals and the 

rest consists of carbon products. To increase the proportion of dry matter 

growers have to restrict the water uptake of the fruit by increasing the osmotic 

potential of the nutrient base solution and in order to maintain the osmotic 



41 

gradient the plants accumulating more solutes in the fruit (Mizrahi, 1982; Hobson, 

1988; Adams, 1991 ). 

1.5.5 Organic Acids as a Component of Flavour 

Organic acids are one of the major taste components of tomato fruit. The acid 

content of the fruit is an important characteristics of processing tomatoes. To 

avoid problems with thermophilic organisms, Stevens (1972) suggested that the 

acid content of the fruit must be high enough to provide a pH of not less than 4.4. 

High ph values however necessitate longer processing times increasing the 

difficulty of obtaining high quality product. 

There is a continual change in the acidity of the tomato fruit during development 

and maturation. The concentration of acids increase during development and 

reach maximum near incipient colour and then decrease until well beyond 

maturity (Stevens, 1972). When fruits are still immature malic acid is 

predominant, whilst citric acid forms only about 25% of the total acidity (Stevens, 

1972). Maximum acidity during ripening coincides with the first appearance of 

pink colour, when malic acid concentration decreases rapidly in !ocular juices 

and in the outer fruit walls (Davies and Hobson, 1981 ). As a result of different 

rates of change during ripening, malic to citric acid ratio rapidly declines. Thus 

citric acid makes a greater contribution to sourness than malic because it occurs 

at a higher concentration (Stevens et al., 1977). Titratable acidity of the outer 

fruit wall is relatively low compared to that of locular contents. 



42 

Should there be any particular change in titratable acidity, it has always been 

attributed to citric acid alone or to changes in both citric and malic acids. 

The relationship between potassium and acidity in tomato fruits is very close and 

highly significant (Varga and Bruinsma, 1986). Potassium accounts for 85% of 

, the total cations in the fruit (Davies and Hobson 1981 ). This relationship varies 

according to the level of the potassium supplied and the growing conditions 

(Besford and Maw, 1975). At high potassium supply, the acidity increases 

(Davies and Winsor, 1967) and the colour and shape improves (Winsor et al., 

1961 ). At low potassium supply, the growth period of a tomato fruit is shortened 

(Besford and Maw, 1975) and the maximum climacteric respiration is enhanced. 

Mengel and Viro (1974) reported that the potassium concentration affected the 

metabolism of the fruit. 

The form of nitrogen applied influences the acidity of the fruit. With ammonium 

nitrogen Varga and Bruinsma (1986) observed the fruit to be less acid in 

composition than with nitrate nitrogen. When high potassium and nitrogen is 

applied the combined effect is particularly favourable to fruit acidity, while 

magnesium and calcium have little effect. Calcium when combined with 

increased potassium lowers the acid content of the fruit. 

Tomato fruit is a valuable source of vitamin C. Typical values of Vitamin C vary 

from 16-25 mg/100 g fresh weight. Extensive literature reported by Hobson and 

Davies (1981) is no doubt a reflection of its importance to human nutrition and 



43 

the contribution that tomato fruit can make. Ascorbic acid content of tomato fruit 

varies. The wide variation is probably attributable to differences in light 

conditions during growth. It is not surprising to note that fruits harvested from 

plants grown outdoor were found to contain more ascorbic acid than fruits grown 

under glass. 

Similar effects of light on ascorbic acid content can be found on fruit positioned 

in the plant depending on their relative exposure to sunlight. Thus, a rise in 

ascorbic acid content with ascending truss position was probably due to 

increasing light intensity. 

1.5.6 Aromatic Volatiles 

The demise of the tomato like flavour is not only associated with the imbalances 

between sugars and acid, but also due to the lack of a desirable aroma in ripe 

fruits. Volatile compounds responsible for the odour of tomatoes are present in 

a relatively small amounts. The odour of freshly picked tomatoes comes from the 

calyx, sepals and in the stalk rather from the fruit per se. The skin of tomato 

fruits has no pores or lenticels so that volatile compounds cannot escape. It is 

only by means of cutting the fruit that we can smell the aromatic compounds. 

There have been extensive studies conducted to identify the volatile compounds 

of fresh tomatoes, but inspite of these trials the actual quantitative concentrations 

has not been reported. Hobson (1988) reported that there are 400 substances 

that make up the odour of tomatoes, but not even one of them has a smell 



44 

reminiscent of a rip~ tomato. The flavour of tomatoes is a combination of aroma 

and the taste components modified by the texture of the tissues and its juiciness. 

Buttery et al., (1988) showed that the pulp and skin had the highest concentration 

of the volatile aroma compounds and no significant contribution related to the 

seeds. 

1.5. 7 Appearan~e as a Quality Attribute of Tomato 

The quality of tomato fruits is determined among other factors by their size and 

shape (Favarro and Pillatti, 1987). Size and shape are quality attributes 

important in marketing tomatoes because it is the first attribute perceived by 

consumers. Size and shape is standard criterion for grading and packaging. 

Bangerth and Ho (1984), reported that fruits within the same truss generally differ 

in their final size, thus, larger fruits develop at the proximal end compared with 

the distal fruits. The differential growth based on their position in the truss is not 

entirely due to competition, because if the number of fruits is reduced, the 

remaining distal fruits still remain smaller. Bangerth and Ho (1984), 

demonstrated that the final size of the fruit can be manipulated by the induction 

sequence in the truss, that is by inducing the growth of the fruit in the distal end 

of the truss ahead of the proximal fruits, a much larger fruit can be produced. As 

discussed previously, ovule number influence fruit size therefore a large many 

seeded fruit is likely to originate from an ovary containing many ovules. 

According to Mizrahi et al. (1988), saline treated plants produce small sized fruits 



45 

as they contain less water and more soluble solids. 

Colour which depends primarily on the content of total carotenoids and ratio of 

lycopene to carotene is another quality attribute of tomato fruit. Most consumers 

prefer deep uniform red coloured tomatoes as a basis for selection. At the 

ripening stage, temperature has a great influence on the rate and extent of colour 

change. Lower than normal temperatures lead to an increase in beta-carotene 

and decrease in lycopene. When tomato fruits are exposed to temperatures 

between 30-40°C they remain yellow rather than red (Davies and Hobson , 1981 ). 

Different morphological regions of tomato fruit vary in chemical composition. 

Total carotenoids are found to be highest in the outer pericarp whereas carotene 

is highest in !ocular region. Mizrahi et al., (1988) observed that fruits from 

salinized plants were redder in colour than the normal fruits. The effect was 

intensified as the conductivity of the nutrient solution was increased. Increasing 

the concentration of potassium in the solution has been found by Dangler and 

Locasio (1990), to reduce the severity of blotchy ripening. 

1.5.8 Firmness and Shelf Life of the Tomato Fruit 

Firmness is a quality factor that determines the shelf life of the fruit. Firm fruited 

cultivars show a great advantage hence fruits can be allowed to ripen on the vine 

until almost 100% of the fruits is ripe. This practice according to Stevens (1980) 

can increase the viscosity of the fruit which provides tomato products with 

increased consistency. Changes in fruit firmness are due to the activity of 



46 

softening enzymes. Since firm fruits have reduced amount of !ocular tissues, 

they exhibited lower rates of respiration and ethylene production during ripening. 

One disadvantage of firm fruited cultivars is that they contain less acid thereby 

lowering their acid· to sugar ratio Stevens (1977). Firmness of the fruit show 

variations along the morphological regions of the fruit. Adegoroye et al., (1989) 

showed that there is a progressive decrease in deformation from stylar end of the 

fruit to the calyx, whilst the shoulder part of the fruit is found to be the weakest 

point. Both epicarp strength, !ocular resistance and firmness decrease, while 

deformation and compliance increase with ripeness. Mizrahi (1988) reported a 

contrasting effect of salinity on the shelf life of tomato. It was observed that 

saline treated plants produce fruits that are slightly firmer, but deteriorated 

somewhat faster than the normal fruits in contrast with their other observations 

showing that the shelf life of the fruit was extended due to a reduce amount of 

water in the fruit. 



CHAPTER 2 

THE EFFECTS OF HIGH CONDUCTIVITY LIQUID FEEDS ON THE 
YIELD AND QUALITY OF OUTDOOR GROWN TOMATOES 

2.1 Introduction 

47 

High yielding good quality outdoor tomato crops are traditionally grown on fences 

in the Otaki district of New Zealand. Crops are harvested from summer through 

to late autumn and are irrigated by using overhead sprinklers. Nutrients are 

applied as a base dressing along with a number of side dressings. 

Trickle or drip irrigation has been used for some time with vegetable crops in 

Israel and is under investigation in the USA with an extensive range of crops 

(Hochmuth, 1992). It has not been used to any extent with outdoor vegetable 

crops in New Zealand. 

Research with greenhouse tomatoes has shown that fruit flavour can be improved 

by the use of high conductivity feeds. The effect of these treatments has been 

to increase the concentration of sugars and acids in the fruit (Anon, 1992). In 

Israel, Pasternak et al. (1986) have shown that total soluble solids of trickle 

irrigated tomatoes was increased by the use of saline water, while Cornish and 

Nguyen (1989) in Australia have shown that high soil electrical conductivity was 

found to increase total soluble solids comparable to that of hydroponic systems 

reported by Hobson (1988). 



48 

The following study was designed to use trickle irrigation to apply high 

conductivity feeds to fenced tomatoes to determine the effects of such treatments 

on fruit yield and quality. 

2.2 Materials and Methods 

2.2.1 Plant Propagation and Transplanting 

On 21 October 1991, seeds of the tomato cultivar Extase were sown in cell 

trays at one seed per cell and placed on a heated bench (24°C). The trays held 

54 plants and 85 mis of growing media per cell. A 50 : 50 peat sand media 

was used (Appendix 1 ). At emergence the seedlings were removed from the 

heated bench and grown on in a greenhouse with a minimum temperature of 

16°C and ventilation at 22°c. 

Thirty days after germination, and thereafter twice a week until the plants were 

ready for planting, the seedlings were fed using a stock solution containing 100 

ppm N, 34 ppm P and 100 ppm K. On , 27 November, one week before 

transplanting, the seedlings were moved out of the glasshouse and hardened off 

outside. 



49 

2.2.2 Land Preparation 

The experiment was conducted during summer of 1991 on Karapoti Sandy Loam 

soil at the Plant Growth Unit at Massey University. The experimental block was 

sheltered and the land was ploughed, rotovated and levelled to prepare a 

planting out tilth to a depth 20 cm. One hundred and fifty soil samples from the 

top 15 cm were collected at random from the 225 m2 experimental area using 

a soil core borer and a sub-sample was submitted to the MAF Laboratory for 

analysis. Ten fences, 1.5 m apart and 15 m long were then erected based on 

the system used in the Otaki district. (Appendix 2). The post were 2 m above the 

ground and were placed 3. 75 m apart in a row. 

2.2.3 Base Fertilizer Application and Transplanting 

The result of the MAF soil test and target values based on the recommendation 

of Clarke et al. (1986) are presented in Table 1. As the soil test data were 

satisfactory, a base maintenance dressing of Nitrophoska fertilizer (12-10-1 0) 

was applied at a rate of 500 kg per hectare before transplanting. The fertilizer 

was applied in band 20 cm. on either side of the row and push hoed into the 

soil. 



50 

Table 1. MAF soil test results and target levels. 

pH Ca p K Mg Na 

Soil Test 6.1 12 41 11 27 7 

Target 
Values 5.3-6.7 10 33-45 13 15 -

On 3 December 1991, forty days after germination,the plants were transplanted 

and watered in while the guard plants were planted a day later. The plants were 

in rows 1.5 cm. apart and 60 cm. apart in the row. 

2.2.4 Treatments and Experimental Design 

There were four treatments, control and three conductivity treatments. The 

control treatment receive no further nutrients and was watered as required. The 

three conductivity treatments were 2, 4 and 6 mS cm-1
• These treatments were 

applied from 31 December and were based on a standard nitrogen-potassium 

greenhouse liquid feed (Table 2) . 

A randomized complete block design was used. A block consisted of 2 rows of 

plants with 2 plots per row (Appendix 3). The experimental plot was 7.2 m long 



51 

and contained ten plants with 2 guard plants at the end of each row and 

between adjacent plots. There were two guard rows at each side of the planting. 

2.2.5 Trickle Irrigation System 

The trickle irrigation system used in this experiment was connected to the 

Palmerston North City Corporation Water Supply. A valve and pressure gauge 

on the main line controlled the delivery to the system. The main line was split 

into 4 submains to deliver the four treatments (Appendix 3). lnline diluters 

(Dosatron 1501) were connected to the 3 submains to supply the conductivity 

treatments and the fourth sub-main supplied water to the control treatment. The 

four sub-mains were laid across the centre of the experimental block. 

In each replicate lateral pipes were connected to the sub-mains according to 

treatment. Typhoon 25 dripper-line with a water inlet 60 cm apart were used for 

the conductivity treatments, while pvc pipe with microsprinklers was used for the 

control plants. The microsprinklers were spaced 1.2 m apart. 

Each microsprinkler was set to water 2 plants, one on each side. The four 

lateral pipes were fixed in place by tying them to wires attached to the posts. The 

layout of the diluters, nutrient tanks, submains and lateral pipes is detailed in 

Appendix 3. 



52 

2.2.6 Preparation of Liquid Feed 

The three conductivity treatments used provided conductivities of 2, 4, and 6 ms 

cm-1
• The liquid f~eds for these treatments were based on a standard 

greenhouse stock solution (Table 2). A series of test dilutions were prepared 

using the above stock solution to determine the right amount of the fertilizer 

required to be dissolved to provide conductivities of 2, 4 and 6 mS cm-1
• 

Figure 1 presents the relationship between the dilution rate and conductivity 

derived from the test solution prepared. 

Table 2. Standard greenhouse tomato stock solution and resulting liquid feed 
(Clarke etal.,1986). 

Composition Dilution 1 :200 
Fertilizer (grams litre-1

) 
N K Mg s 

(ppm) (ppm) (ppm) (ppm) 

Potassium 150 105 285 0 0 
Nitrate 

Urea 30 57.5 0 0 0 

Magnessium 50 0 0 60.75 80 
Sulphate 

The dilutions of the standard stock solution (Table 2) that provided the desired 

conductivities were read off the graph (Figure 1) and then used to determine the 

stock solutions that when diluted 1 :, 00 would produce the three treatment 

conductivities (Table 3). 



Figure 1. Relationship between dilution rate and conductivity of liquid feed. 

6-,----------------------'----

11 :1051 
5.5 

- 5 E 
~ 
~ 4.5 
........... 

~ :s: 4 
u 
::J 

"O 3.5 
C 
0 
() 

3 

2.5 

25 

1 :46 

50 
Dilution rate 

100 

53 



Table 3. Determination of stock solution (1:100) dilution required for three 
conductivity treatments. 

Dilution Potassium Urea Magnesium 
Treatment required (read Nitrate Sulphate 
(mS cm-1

) off from graph) 
Amount required grams litre-1 

(Dilution 1:100) 

2 1 :105 142.85 28.60 47.20 

4 1 :46 326.10 65.22 108.70 

6 1 :29 517.50 103.50 172.50 

54 

Stock solution were then prepared which when diluted 1 :100 provided the 

treatment solutions detailed in Table 3. Since the weight of potassium nitrate 

required to provide the 6 mS cm-1 treatment exceeds its solubility two stock 

solutions each capable of supplying 3 mS cm-1 were used . 

2.2.7 Irrigation Schedule 

Irrigation requirement of the plants was calculated based on a crop factor, area 

per plant and potential evapo-transpiration. Assuming that the area per plant is 

50% of the true area, each plant occupied 0.45 m2
• The crop factor for 

greenhouse tomatoes of this size is 1.2 ( White, 1989). Thus for every millimetre 

of evapotranspiration, 0.54 litres of water is required by each plant. As the 

average potential evapotranspiration is 4mm day-1
, each plant will require 2.16 

litres of water daily. The water requirements for control plants was based on soil 

moisture deficit. If the estimated soil moisture deficit did not exceed 28 mm per 

week no irrigation was applied to the control plants. 



55 

Information regarding soil moisture deficit were taken from rainfall data from 

DSIR, Grasslands Division and potential evapo-transpiration (4 mm day-1
). Based 

on this information, there were only four occasions from January to April when 

the soil moisture deficit exceeded 28 mm. However control plants were irrigated 

only twice as on two of the occasions that the deficits exceeded 28 mm there 

was heavy rain before the irrigation could be applied (Appendix 4). Water was 

applied for two hours on the two occasions irrigation was supplied. 

2.2.8 Conductivity Treatments 

The conductivity treatments were applied from 31 December 1991. At this 

stage setting in the first truss had commenced on 50 % of the plants. The 

conductivity treatments were irrigated every 2 days thereafter for a duration of 

two hours. This applied 3.6 L of liquid feed per day. The conductivity of the 

treatment solutions was monitored after irrigation at different locations using a CF 

meter. 

2.2.9 Plant Training and Protection 

The Otaki system sit training and supporting tomato plants was used. This was 

done by erecting 4 posts ( 15 cm in diameter and 2.5 m long) in a row set 3. 75 

m apart to a depth of 60 cm. End row posts were angled to take the strain once 

the wire supports were stretched the length of the rows. The rows were 15 

meters long. 



56 

A pair of wire was attached to the posts at 30 cm intervals from the ground. 

Plants were trained between pairs of wires which were laid out as the plants 

required support. Plants were trained to two stems. The second or lateral stem 

was produced from ·the axil of the leaf immediately below the first inflorescence. 

The first pair of wires was attached 25 days after planting. The two stems were 

delateraled at regular interval and the plants were stopped by removing the top 
l 

of the plants with a: knife at two meters. 

A push hoe was used once every two weeks to control weeds. A regular weekly 

spray programme was carried out for disease and pest control. Details are 

presented in Appendix 5. This programme was repeated every three weeks. 

2.2.10 Harvesting and Grading 

To provide details and information about the position on the plant were the fruits 

were harvested, each truss was labelled using different colour tags according to 

their position on the individual stems. Fruits were harvested once they reached 

a red orange colour. There were two harvests per week for the first two weeks 

and three harvests per week thereafter. Harvesting commenced on March 9 with 

the final harvest on May 1, 1992. 

Fruits were harvested on an individual truss basis for each treatment. Each fruit 

was weighed individually and graded according to size (diameter) with reject fruits 

being allocated to 5 classes . 



57 

Fruit sizes were classified using the grading chart recommended and issued by 

New Zealand Fresh Tomato Industry (Plate 1 ). Fruit were therefore graded to the 

following diameters; 70+, 60-70, 50-60, 40-50, 40 mm and below. These sizes 

were coded as grades 1-5. For fruits to be considered marketable they were free 

from physical damage and uniform in shape and colour. Rejected fruits were 

indexed as cracked, rough, blossom end rot, blotchy and diseased. 

Fruit weights were determined by weighing the fruit individually using a Mettler 

scale, interfacing with a laptop computer and printer to record the weight along 

with the information on fruit size and grade (Plate 2). Total yield was computed 

as combined weights of marketable and rejected fruit. This however did not 

include the fruits that abcissed from the trusses before they were ripe and those 

that were damage by birds, as it was difficult to identify where on the plant such 

fruit originated. 

2.2.11 Assessment of Fruit Quality 

Ten sample fruits were chosen at random from the fruit harvested from each 

treatment plot once a week for six consecutive weekly harvests starting from 

March 19, 1992. · Sample fruits were of the same size and maturity with 

diameters ranging from 50-60 mm. Since the fruits were harvested when orange 

red, they were ripened at ambient room temperatures until the red ripe stage 

was reached before quality assessments were made. All quality assessments 

were carried out on the same day. 



58 

2.2.11.1 Fruit Firmness 

Firmness of sample fruits were measured by using a penetrometer. 

Measurements were taken from th