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    Comparison of heritage and modern crop cultivars in response to irrigation and nitrogen management : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
    (Massey University, 2012) Fandika, Isaac Rhinnexious
    There is a resurgence of interest in heritage crop cultivars (potatoes, squash and yams) in New Zealand because of the premiums farmers get at niche markets. However, a paucity of information in relation to their growth characteristics and resource use efficiency limit successful management of these crops. This research compares the response of different heritage and modern crop cultivars to irrigation, nitrogen (N) fertiliser and canopy management. Some heritage cultivars produced as much marketable yield as modern cultivars while other heritage cultivars had low yields. Modern potatoes were more responsive to irrigation and N than heritage potato crops (collectively known as Taewa). Application of more than 80 kg N ha-1 decreased yield in Taewa (Moe Moe, Tutaekuri) whereas, it increased the yield of modern potatoes (Agria, Moonlight). Full irrigation (FI) increased yield in modern potatoes and Moe Moe. In contrast, Tutaekuri yield was greatest with partial irrigation (PI). FI and 80 kg N ha-1 are recommended for Moe Moe production whereas PI and less than 80 kg N ha-1 are recommended for Tutaekuri. In addition, greater tuber dry matter and low sugar content suggest that Taewa would have better cooking and processing qualities than modern potatoes. Heritage crops required more water than modern crop cultivars because they mature later. There was high ‘water use efficiency’ in heritage pumpkin squash; high ‘irrigation water use efficiency’ in modern potatoes and high ‘economic water productivity’ for heritage potatoes and pumpkin squash. Heritage crop cultivars adapted to water deficit by developing more roots, higher photosynthetic WUE and leaf water potential than modern cultivars. Although total biomass production was similar, heritage crops tended to produce less marketable yield than modern cultivars because of excessive vegetative growth and potato psyllid infestation. Two strategies to manage the canopy and reduce vegetative growth using chlorocholine chloride (CCC) and mechanical topping were developed. Both strategies increased marketable yield in Taewa by 32 - 44%. Application of CCC at 25 and 50 days after emergence (DAE) was recommended for irrigated Taewa, whereas mechanical topping and application of CCC at 25 and 30 DAE were recommended for both irrigated and rain-fed Taewa. The study also observed that potato psyllid need to be controlled up to 170 DAE in Taewa to avoid yield loss equivalent to NZ$10, 485 to NZ$17, 412 per ha. This study contributes to policy on sustainable and improved Maori land use. It can be concluded that premium market prices are important to the success of heritage crops (i.e. to maintain their high ‘economic water productivity’) whereas modern crops might use irrigation water more efficiently (i.e. greater ‘water use efficiency’). It is evident that heritage crops can be grown successfully, and that on occasions they use valuable resources efficiently. To enhance water use efficiency, management of heritage crops should focus on improving the harvest index.
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    Studies of the factors affecting the yield and quality of single truss tomatoes : a thesis presented in partial fulfilment of the requirements for the degree of Doctorate of Philosophy in Horticultural Science at Massey University
    (Massey University, 1996) Morgan, Lynette Stella
    This research was conducted to evaluate the potential of the single truss system of tomato production to produce high yields of quality fruit under New Zealand conditions. The NFT hydroponic system was used to grow the plants so that nutrient solution conductivity could be maintained close to predetermined levels. In the first experiment three cultivars were compared. At the time of fruit set of the first truss four conductivity treatments (2, 4, 6 and 8 mS cm-1) were applied. Yield and fruit quality data was obtained from each of six crops over an 18 month period. Yield (fruit size) decreased with increasing conductivity for all three cultivars. Season also had a significant effect on yield, with an April harvested crop having the highest yield. Both fruit brix and titratable acidity were increased at the higher conductivity levels. There were also cultivar and seasonal differences in fruit quality, with the cherry cultivar 'Cherita' consistently producing the highest brix and titratable acidity levels. Brix levels were found to be low in the December harvested crop, while acidity was highest in the December, April and July harvested crops. Season, solution conductivity and cultivar influenced plant leaf area and leaf area index. Solution conductivity also effected foliar mineral levels, as did cultivar. Three successive multi truss crops were grown in a pumice media system to provide fruit quality data for sensory evaluation and comparison with single truss and commercial compositional fruit quality. The same three cultivars as were compared in the single truss crop experiment were grown at three conductivity levels (2, 4 and 6 mS cm-1) applied at the time of fruit set of the first truss. Fruit samples were taken from the 5th and 6th trusses for quality evaluation. Season and solution conductivity had an effect on fruit dry matter percentage and brix. Fruit shelf life was affected by season, conductivity and cultivar, with a longer shelf life obtained from fruit grown at the higher conductivity levels. The December harvested crop had the lowest overall shelf life. Fruit firmness was only affected by solution conductivity, with the fruit from the higher conductivity treatments being firmest. Sensory evaluation of Rondello fruit on three separate occasions showed that the higher conductivity treatment scored highest for most attributes, and that these sensory scores correlated well with brix and titratable acidity levels. A second single truss crop experiment focused on manipulation of the source/sink relationship (fruit and leaf number combinations) of three successional crops and the effect of spring and winter CO2 enrichment on two of the three crops. The summer crop also evaluated the effect of crop shading and source/sink relationship on fruit yield, as high fruit temperatures were suspected to have reduced yield in the previous summer single truss crops. Yield and fruit quality data was collected from all three crops, along with fruit and environmental temperature recordings from the summer crop. It was found that season and fruit number effected yield, with the 8 fruit per plant treatment resulting in the greatest yield. Leaf number (either 2 or 3) and season affected fruit dry matter percentage, brix and leaf area, while fruit number influenced brix levels. CO2 enrichment (1000 ppm) had no effect on either spring or winter fruit yield, but did advance crop maturity allowing an extra crop per year to be produced. Thus yearly yield was increased by CO2 enrichment. CO2 enrichment improved fruit quality in the spring crop, but had no effect on the winter crop. Shading of the summer crop resulted in an increase of 10% in total fruit yield and 19% in marketable fruit yield, due to the presence of smaller fruit and heat induced ripening disorders in the unshaded crop. Both leaf number and shading treatments affected titratable acidity, with unshaded fruit having greater percent citric acid levels. Shelf life and fruit firmness was greater in the shaded crop. Air, canopy and fruit temperatures were reduced under shade, with exposed fruit often reaching extreme temperatures (above 40°C). Having established that leaf and fruit temperatures were reaching extreme levels during the summer in a single truss cropping situation, the effect of these temperatures on photosynthesis and fruit respiration was examined. The effect of leaf age on photosynthesis was also examined as single truss plants do not continue to produce young foliage to maintain photosynthesis levels. After harvest, net photosynthesis and the light compensation point, which had been increasing began to fall rapidly at all light levels. It was found that after an initial drop as leaves matured, leaf age did not effect net photosynthesis. Plants exposed to 800 PAR showed maximum net photosynthesis at temperatures between 25 – 27°C. Net photosynthesis ceased at 43°C. Fruit truss respiration rates were determined at 4 temperatures (25, 30, 35 and 40°C), on 3 occasions (18, 26, 36 and 40 days after fruit set). 5 different tissue sample combinations were assessed comprising, the whole truss with sealed and unsealed cut surfaces, fruit only with sealed and unsealed calyx scar and calyx, peduncles and plant stem only. It was found that temperature, truss portion assessed and stage of fruit maturity all affect fruit respiration rate, with the fruit only (calyx scar unsealed) resulting in the greatest CO2 efflux. It was concluded that while the fruit epidermis is relatively impermeable to gas escape, the main route for Co2 is through the calyx scar. Mature green fruit had the greatest response of increased CO2 production with increasing temperature, while temperatures above 25°C disrupted the climacteric pattern of CO2 evolution. It was concluded that in single truss plants, when temperatures were above 30°C, net photosynthesis is reduced, while fruit respiration begins to increase rapidly, both responses having a detrimental effect on yield. The single truss system was shown to produce yields and fruit quality equal to those of good multi truss commercial tomato producers in New Zealand. This was achieved by CO2 enrichment for crop advancement and summer crop shading, while moderate levels of solution conductivity produced good quality fruit. However, there is the possibility of further improving these yields by utilisation of other technologies such as a movable bench system and manipulation of plant density, timing of conductivity application, and different cultivars. The potential of this system for high quality, high yielding tomato fruit production warrants commercial evaluation.
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    Fruit composition, growth, and water relations of Braeburn apples under reduced plant water status : this thesis is presented in partial fulfilment of the requirements of the degree of Doctor of Philosophy in Horticultural Science at Massey University, Palmerston North, New Zealand
    (Massey University, 1996) Mills, Tessa Marie; Mills, Tessa Marie
    Water plays a major role in the physiological processes of plants. Effective irrigation relies on a comprehensive understanding of the impact of water on plant processes. As water becomes an increasingly scarce resource, the impact of reduced plant water status on crop performance (quality and yield) requires investigation. The effects of reduced plant water status on fruit composition, growth, and water relations were therefore studied using both field-grown and container-grown 'Braeburn' apple trees. Vegetative growth and carbon assimilation were also measured. Plant water deficit was imposed at various times during the growing season. The treatments were: control, which was fully irrigated during the experimental period, entire-season deficit, deficit irrigation from 55 days after full bloom (DAFB) until final fruit harvest (183 DAFB), early-season deficit (from 55 - 100 DAFB) followed by rewatering, and late-season deficit (from approximately 105 DAFB until final harvest). Reduced leaf water potential developed in all deficit irrigated trees during the stress period. Only the entire-season deficit irrigation treatment resulted in a significant reduction in vegetative growth as measured by total leaf area, shoot growth, and trunk growth. Return bloom was reduced under an early-, but not late-season deficit. Photosynthesis was generally reduced in water deficit treatments, as was stomatal conductance. Only an entire-season deficit irrigation reduced individual fruit weight. Fruit soluble solids and sugar concentration were generally increased under deficit irrigation treatments. However, upon rewatering of the early-season deficit trees, the values again became the same as controls. Fruit mineral concentration did not show consistent differences between treatments and the incidence of storage disorders was low in all treatments and unaffected by deficit irrigation. Early-season water deficit lowered both fruit water potential and osmotic potential. Despite turgor maintenance within the fruit during the stress period, growth was reduced at this time. A late-season water deficit did not modify fruit water relations. It appears that 'Braeburn' fruit are resilient to periodic water deficit during the season, and that water conservation is possible with limited impact on total crop yield. Additionally, a late-season deficit may even enhance some fruit quality attributes, such as increased total soluble solids. An early-season deficit reduced return bloom and must therefore be used with caution. An entire-season water deficit is not recommended due to the reduction in fruit size.
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    Dry matter and nitrogen partitioning in sweet corn (Zea mays L.) for processing : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University
    (Massey University, 2000) Hansen, Luke N.; Hansen, Luke N.
    Increasing land values without comparable increases in yield or reduced input costs have reduced the attractiveness to growers of processing sweet corn (Zea mays L.) as a cropping enterprise at Gisborne, New Zealand. As a consequence, the problem of consistently sourcing adequate volumes of raw material has been one factor leading the region's major sweet corn processor to consider withdrawing from the region. Hence, the development of agronomic practices which reduce crop production costs, improve marketable yields, or both, will be important for maintaining the viability of the sweet corn processing industry in Gisborne for both growers and processors alike. Two of the most important factors influencing yield of sweet corn are plant density and nitrogen (N) nutrition. The density range which maximised marketable yield of cobs and kernels for Jubilee and SS42, the two prominent cultivars grown at Gisborne, was 69-77,000 plants per hectare. Although yield response to fertiliser N was also investigated in the same study, the yield response was either negligible (SS42) or did not follow a trend consistent with incremental increases in N rate (Jubilee). The limited response was attributed to high background levels of soil available N (269 kg/ha). A second experiment was designed to investigate the yield response, to fertiliser N on a soil with a low available N level. Although only 92 kg N/ha was available from the soil, yield response in this experiment was also negligible with N rates greater than 73 kg/ha. Combining the two years' results indicated that yield response to N fertiliser will be limited when soil available N levels are > 213 kg/ha. The rate of yield improvement could be enhanced by greater understanding of the physiological processes limiting yield in maize and sweet corn. The study of source-sink relationships can provide useful insights into yield determinants. A field experiment was established with Jubilee and SS42 to study how variables influencing weight of primary and secondary ears (e.g., silk delay, tiller number per plant) adjust to plant density and N nutrition. Path analysis and canonical discriminant analysis indicated that tillers were important for supplying the secondary ears of both cultivars with photoassimilate at low densities (e.g., 40,000 plants per hectare) and were important for Jubilee, but not SS42, at high densities (e.g., 100,000 plants per hectare). A short silk delay for both the primary and secondary ear was important for both cultivars at low densities to establish a large ear sink. Thus, at low densities, the presence of a secondary ear at low densities appeared to enhance kernel development on the primary ear. To further understand the partitioning of DM and N to kernels, further experiments quantified sink strength (or source strength) of an organ (i.e., leaves, stems, roots, kernels, rachis, husk, or shank) between defined ontogenetic stages. Sweet corn grown at 70,000 plants per hectare with rates of applied N ranging from 0 to 230 kg/ha were harvested throughout ontogeny until R4. Although N rate generally did not influence partitioning of N or dry matter (DM) to any organ, significant cultivar differences were detected. Kernel sink strength of Jubilee was two-fold greater for DM than SS42 and three-fold greater for N between R1 and R3. As a consequence, kernels of Jubilee contained 34% more DM than those of SS42 at R4 and were significantly more efficient than SS42 kernels at translating endogenous N into kernel DM. The observation that DM was partitioned to vegetative organs during reproductive growth while N was being remobilised from these organs indicated that both Jubilee and SS42 were source limited for N, yet sink limited for current photoassimilate. No published studies have been sighted which have identified a link between the source limitation for N and the sink limitation for DM in Z. mays. Investigating source-sink, relationships indicated that the two events are linked and initiated by low kernel sink strength during early grain filling. SS42 partitioned large proportions of DM to both husks and stems between R1 and R3, in contrast to Jubilee which partitioned most DM directly to kernels. As partitioning DM to vegetative tissue and husks reflects photoassimilate not consumed in reproductive growth, excess photoassimilate resulting from limited sink strength may have decreased photosynthetic rates through 'feedback' inhibition. Consequently, the ability of Jubilee to partition DM to roots for N assimilation between R3 and R4 may reflect less inhibited photosynthesis than for SS42. A subsequent experiment provided further evidence that kernel sink strength influences N and DM partitioning. This experiment also indicated that low kernel sink strength during early grain filling may actually initiate an inhibitory cycle. When maximum leaf area in maize and sweet corn is reached around R1, the ear is a relatively weak sink and unable to accumulate all the photoassimilate being produced. Although the excess is partitioned to stems and husks, these organs can only accumulate a limited quantity before they become saturated. When the stem and husks become saturated, photoassimilate may accumulate in leaves causing feedback inhibition of photosynthetic enzymes to reduce the supply of photoassimilate. However, as N assimilation rate is dependent on the rate of photoassimilate supply to roots, the inhibited photosynthesis reduces N uptake and as a consequence, remobilisation of N is stimulated. Excessive remobilisation of N from leaves may further impair photosynthetic activity to further restrict the photoassimilate supply for root and shoot functions including grain filling. Hence, an inhibitory cycle may evolve from the limited capacity of kernels and rachis to accumulate photoassimilate. Since SS42 (sh2 mutant) had a significantly lower kernel sink strength than Jubilee (su1 mutant) during early grain filling, SS42 was apparently more influenced by the inhibitory cycle than Jubilee. To add support to the theory that limited kernel sink strength during early grain filling may lead to an inhibitory cycle, a final experiment investigated the association of the endosperm storage protein, zein, with kernel sink strength. A high correlation (r=0.91) was observed between kernel DM and the level of zein. Further, the wild type (Furio) contained 25 and 49% more zein at R4, and accumulated 18 and 49% more DM, respectively than the su1 (Jubilee) and sh2 (SS42) mutants. Similarly, kernels of Jubilee, which contained 31% more zein than those of SS42., accumulated 38% more DM. Together these results indicate that the level of zein is associated with kernel sink strength and thus lends support to the inhibitory cycle theory.