Massey Documents by Type
Permanent URI for this communityhttps://mro.massey.ac.nz/handle/10179/294
Browse
7 results
Search Results
Item Growth studies with lettuce (Lactuca sativa L) : a thesis presented in partial fulfilment of the requirements for the degree of Master of Horticultural Science in Plant Science at Massey University(Massey University, 1974) Lee, Kong KianIn a sand culture experiment carried out in a heated glasshouse, the effect of five levels of P (ranging from 7.75 p.p.m. - 124 p.p.m. on the growth of two cultivars of lettuce was examined. Samples were taken at weekly intervals for ten weeks and growth analysis, and chemical analysis of the whole plant were carried out for total N, P and K from the samples. Significant differences between cultivars were found for net assimilation rate and leaf area ratio, with a slightly higher relative growth rate in young 'Cobham Green' plants. 'Cobham Green' had a greater leaf area ratio but smaller net assimilation rate than 'Webb's Wonderful' . The higher relative growth rate of Cobham Green at the early stages of growth was mainly due to its higher leaf area ratio, but net assimilation rate became an important component during later growth stages, possibly as a result of mutual shading. Within each cultivar, however, the variation in relative growth rate was based on net assimilation rate rather than in leaf area ratio. Both dry weight and the percentage of total P increased with increase in P supply. The percentages of total N and K decreased towards the market maturity but no general trend was observed in the percentage of total P.Item Colonisation of lettuce by Listeria monocytogenes and its biofilm formation : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Microbiology at Massey University, Manawatu, New Zealand(Massey University, 2020) Kyere, Emmanuel OwusuFoodborne outbreaks associated with fresh produce due to pathogenic bacteria such as Listeria monocytogenes (L. monocytogenes) are increasing. A survey conducted as part of this study showed 5% of bagged lettuces sold at retail outlets contained L. monocytogenes. The ability of L. monocytogenes to form biofilms is a concern in terms of fresh produce safety. The use of hydroponics (growing plants in nutrient solution without using soil) in fresh produce production is a more controlled environment than soil, and therefore may be easier to prevent pathogen contamination. The aim of this study was to determine whether hydroponic grown lettuce and UV-C stress can reduce the colonization, growth and biofilm formation of three fresh produce related strains of L. monocytogenes: PFR O8A06 (coleslaw isolate), PFR O8A07 and PFR O8A08 (cabbage isolates) on lettuce. Evaluation of the nutrient content and indigenous microbiota between hydroponic and soil grown lettuces revealed significant differences. 16S rRNA amplicon sequencing of the bacterial community associated with hydroponically grown lettuce showed that it was more diverse than soil-grown lettuce. Pseudomonas was found to be the dominant bacteria on hydroponically grown lettuce while Bacillus was found to be dominant in soil grown lettuce. There was no significant difference (p > 0.05) in L. monocytogenes attachment to both hydroponic and soil grown lettuce leaves under minimal exposure times. Exposure of lettuce to 5 log CFU/ml for just one second resulted in at least 0.77 log CFU/cm² attachment. L. monocytogenes was able to survive and grow on both lettuce leaf surfaces at 4 and 10°C. Both hydroponic and soil grown lettuce leaf extracts enhanced the survival, growth and biofilm formation of L. monocytogenes on stainless steel coupons, representing surfaces in lettuce processing plants. The results of this study demonstrate the ability of L. monocytogenes to colonize and form biofilms on lettuce irrespective of the growth system used. Finally, UV-C (1.3 kJm⁻²) on lettuce produced a stress response in the plants that reduced L. monocytogenes attachment, survival and growth at pre-harvest. Further exploration of this technique may enhance the microbial safety of lettuce.Item A study of the leafspot disease of lettuce caused by Stemphylium botryosum Wallr. : a thesis presented in partial fulfilment of the requirements for the degree of Master of Agricultural Science in the University of New Zealand, Massey Agricultural College(Massey University, 1961) Slade, Donald ArthurLettuce (Lactuca stavia L) is the most important salad crop and a principal vegetable of New Zealand where in many districts it can be grown out of doors all the year round. Winter lettuce growers commonly plant from 1/2 - 5 acres of lettuce, and a good crop will cut 400 cases an acre. In late winter and early spring when other vegetables are scarce, returns to the grower from lettuce may be as high as 20/- to 60/- a case. Returns per acre from winter lettuce are therefore relatively high compared with other winter crops. The success of this crop is of major importance to the grower who commonly depends on it to cover the high winter and spring labour expenses which usually coincide with a period of low production. From season to season and even from week to week in the same season, the quality and quantity of lettuce available is a direct reflection of the prevailing weather conditions. Weather may act directly on the lettuce plant affecting its rate of maturation, appearance and plant size. Weather may also have a profound indirect effect by providing conditions conducive to disease development. It is well recognised that a disease may reach epiphytotic proportions only if weather conditions are favourable to the causual organism. [From Introduction]Item UV-B priming for disease resistance : the use of UV-B light to reduce susceptibility of lettuce plants to downy mildew disease : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Pathology at Massey University, Manawatū, New Zealand(Massey University, 2019) McLay, EmilyBiotrophic disease is one of the largest causes of decreased yield in horticulture. Integrated Pest Management (IPM) systems are required to control disease in a manner which is effective and sustainable, yet there are still a limited number of new approaches available. Pretreatments of UV-B light (280-320 nm) have been previously observed to reduce plant susceptibility to disease, and may be a potential disease control tool to use as part of an IPM approach. Here, I characterised the capability of UV-B LED technology to reduce susceptibility of a range of lettuce (Lactuca sativa) cultivars to downy mildew disease caused by the obligate biotroph Bremia lactucae. Reductions in disease susceptibility of UV-B-pretreated plants was observed as: delayed disease incidence, reduced visual disease rating and lower B. lactucae conidia count. UV-B-induced reductions to conidia counts were sufficient to reduce the infectivity of the diseased plant. Secondary infections caused by UV-B-pretreated plants exhibited yet further reduced disease severity. UV-B light has been observed to induce a similar gene expression profile to that of disease defence in plants. To determine the mechanism of a UV-B-induced disease defence, similarities between UV-B and disease defence pathways were identified. Analysis of previously published gene expression data revealed similarities in flavonoid-related gene expression between exposure to UV-B light in Arabidopsis thaliana, and resistance to downy mildew (Hyaloperonospora arabidopsidis). The specific role of flavonoids in UV-induced defence was further investigated, with B. lactucae conidia counts of lettuce plants negatively correlated with flavonoid level in a UV-B-dependent manner. LC-MS was used to identify metabolic features which contribute to this correlation, and of these, quercetin 3-O-(6″-O-malonyl)-β-D-glucoside had the strongest negative correlation with B. lactucae conidia count. The direct effect of quercetin 3-O-(6″-O-malonyl)-β-D-glucoside was tested through infiltration into lettuce leaves followed by subsequent downy mildew infection. Decreased B. lactucae conidia count was observed in two lettuce cultivars infiltrated with quercetin 3-O-(6″-O-malonyl)-β-D-glucoside concentrations similar to those induced by a UV-B-treatment. It was concluded that UV-B-pretreatments can decrease disease susceptibility to downy mildew in lettuce, and that this defence is underpinned in part by UV-B-induced phenolics. These findings highlight the opportunity for UV-B morphogenesis to be exploited in the development of next-generation, sustainable disease control tools.Item Investigation of relationships through which biodynamic growing practices affect plant growth and nutrient composition : a thesis presented in partial fulfilment of the requirements of the degree of Master of Science in Soil Science at Massey University(Massey University, 2003) Bacchus, GillMore research attention has been paid to development of indicators of soil quality in relation to environmental sustainability than to food quality. Challenges in measuring and showing relationships between soil quality, food quality and human health are discussed. Comparative and long-term studies have shown that organic and biodynamic farming methods and use of composts and manures favourably affect soil quality, enhancing organic matter content and soil organism activity. However, measured effects on food quality have been lacking or inconsistent. Antioxidants, nitrates, trace elements, protein quality and ratios between element concentrations can be measured in assessing food quality. Many of these factors vary considerably with growing conditions and soil management techniques. Effects of factors such as water, light, soil type, variety and nutrient supply on lettuce growth, lettuce nutrient requirements, and recent research into effects of light on plant signalling and nitrogen metabolism arc reviewed and discussed. Recent research into factors influencing food quality has focussed on integration of growth and differentiation forces into "Vital quality" food. The biodynamic field-spray preparations 500 and 501 are used to balance effects of growth or "shade" forces from humus and fertilisers with the differentiating or "light' forces on plants. Literature indicates that the preparation 501 (silica-spray) appears to increase plant nutrient assimilation and production of more complex organic acids. Similar effects have been found for silica compounds applied to soil or nutrient solution. The main objective of the experimental work conducted for this thesis was to investigate whether relationships exist between soil management techniques and application of biodynamic sprays and plant product quality. Transplanted lettuces (cv. Canasta) were grown in a factorial designed field trial on Te Puke Series sandy loam with six treatments: control, soluble fertilisers (DAPCAN) and compost, each with, or without, biodynamic field-sprays 500 (twice) and 501 (3 times). High variability between plants within treatments and small differences between treatment means for most parameters measured prevented many statistically significant differences or relationships being found. Compost amendments appeared to enhance water and nutrient uptake during a dry season. However compost application at a rate to provide equivalent nitrogen to the soluble fertilisers resulted in high leaf concentrations of nitrates and potassium and low DM% and concentrations of sugars, antioxidants, calcium and magnesium. Plants in treatments given compost had highest yields; highest N, P and K concentrations at 28 days from transplanting (DAT); and highest K at 48 DAT. Plants in treatments given soluble fertilisers had highest Ca, Mg, Fe, Zn. and Cu concentrations and greater Ca: P and K: Ca + Mg ratios at 48 DAT. Application of biodynamic field-sprays appeared to have different effects on the plants in plots, depending upon whether they received compost or not. Plants in treatments given field-sprays but no compost had generally small head weight, greater dry matter % and root: shoot ratios at 28 DAT, and highest crude protein and Ferric reducing ability of plasma (FRAP) antioxidant concentration at 48 DAT. Plants in the biodynamic treatment, given compost and field-sprays, had highest P uptake between 28 and 48 DAT and highest fresh-weight at 48 DAT. Measurements of nitrate and sugar contents of leaf cell sap and amino acid concentrations in leaves yielded few, or no, significant differences between treatment means. Microbial activity measured by soil respiration ex situ at 28 DAT was highest in composted plots and lowest in sprayed plots. Measurement of AM fungi colonisation of roots gave inconclusive results. In a sensory evaluation, no significant differences in taste, bitterness, sweetness and preference ranking were found between lettuces from the different treatments. A greenhouse pot trial was undertaken to study the effects of the biodynamic silica spray in more detail. Lettuce transplants (cv. Cos Little Gem) were grown in the same soil and biodynamic compost as were used in the first trial and preparation 500 applied. Half the plants were sprayed 3 times with preparation 501. Measurements before and after the last spray time yielded insignificant differences in light absorption at most wavelengths, net photosynthesis and nitrate, sugar and amino acid concentration in leaves. Silica sprayed plants had higher rates of transpiration and stomatal conductance and higher estimated light absorption of blue and near infrared wavelengths 21/2 hours after spraying. Mainly inconclusive effects of treatments were due partly to the large natural plant to plant (within replication) variation. It was concluded that organic and biodynamic management of lettuces may result in some favourable quality attributes compared to soluble fertilisers but not necessarily all. Results are likely to be specific to particular climatic and soil conditions. It is recommended that further trials be carried out to evaluate influences of biodynamic practices on vegetable food quality in controlled, well-replicated conditions, to improve likelihood of showing statistical differences between treatments. Such trials are needed in a variety of soil, climatic and management conditions, to better understand how different conditions and their interactions affect food quality parameters. Relationships between biodynamic preparation application, soil biota populations and activity, plant metabolism and food product quality, particularly nitrogen assimilation into complex molecules such as essential amino acids, should be explored.Item A study of the effects of temperature and photoperiod on vegetative growth and seed production of leaf lettuce (Lactuca sativa L.) : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Seed Technology(Massey University, 1985) Sukprakarn, SuteveeThree leaf lettuce (Lactuca sativa L.) cultivars. Thai, Grand Rapids and Slobolt were grown in a controlled environment at either 25/l5°C or 30/20°C day/night temperatures and at 10, 12 or 14 hours daylength. Leaf fresh weight, dry weight, leaf area and leaf number all increased with increasing temperature and photoperiod. Slobolt produced a higher vegetative yield than Thai and Grand Rapids. Long days and high temperatures hastened stem elongation. Flowering in Thai and Grand Rapids was mainly influenced by high temperature whereas Slobolt required both high temperatures and long days. Slobolt however, was considerably delayed in bolting and flowering compared with the other two cultivars. Lettuce plants showed two definite flowering peaks over a 50-day flowering period. Slobolt produced only one peak at 25/l5°C due to its slow bolting character. Seed development studies were carried out on plants grown in both the 25/15°C and 30/20°C temperature regimes and at 12 hours daylength. The higher temperature regime hastened seed maturity, germination and shattering. Lettuce seed reached physiological maturity 11 days after anthesis at 30/20°C and 13 days after anthesis at 25/15°C, when the seed head had just begun to turn brown-green. Germination capacity also reached its maximum at this stage. Shattering however, occurred about two days after seed maturity at 20% moisture content at 30/20°C and 4 - 5 days later at 25/15°C. The three lettuce cultivars used in this study produced seed successfully in all treatments. Optimum time of harvest was found to occur when the majority of seed heads had turned slightly brown in colour and was also reduced by higher temperatures and longer daylengths due to earlier bolting and flowering. Highest seed yield was obtained under long days (14 hours). Grand Rapids produced higher seed yields than Thai and Slobolt. High seed yield was related to increased branch and flower numbers, percentage of seed set or seed numbers per head and time of harvest. Good seed set was obtained only under longer daylengths at high temperature while at 25/15°C, daylength was relatively unimportant. Final seed germination was unaffected by temperature or daylength. Practical application of the results which are relevant to Thailand conditions are discussed.Item Growth studies with lettuce : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University(Massey University, 1970) Nichols, Michael AdairGrowth studies were made in the field using two cultivars of head lettuce, Webbs Wonderful (a crisphead type) and Cobham Green (a butterhead type). In a fertiliser and density experiment using a systematic spacing design superimposed on a rotatable fertilizer design evidence is presented to suggest that the 'normal' reciprocal yield-density model W -1 = Aρ + B (when W is the mean plant weight at density ρ, and A and B are constants) is only applicable when there is competition at all densities. A 'modified' model is proposed which includes an additional parameter C, the density at which competition begins. The modified model is: W -1 = Aρ + B if ρ > C W -1 = AC + B if ρ ≤ C The plant weights in a non-competitive situation were fitted to a logistic model using a 'heat unit' environmental time scale, and an analysis of the logistic parameters showed a response only to serpentine superphosphate. This quadratic response was due to an increased relative growth rate (due mainly to an increased net assimilation rate) from the use of serpentine superphosphate up to 40 cwt./acre. At low plant densities Webbs Wonderful hae a higher relative growth rate compared with Cobham Green due to a slower rate of leaf production, and a higher net assimilation rate. This net assimilation rate difference is attributed to the heavier leaves of Webbs Wonderful being light saturated at a higher radiation level than the leaves of Cobham Green. This theory is supported by the similarity in the yields from the two varieties at high densities. The optimum marketable yield spacing for Cobham Green was found to be 1.4 plants/sq.ft. and for Webbs Wonderful 1.1 plants/sq.ft. In spite of a lower plant density the marketable yield from Webbs Wonderful was approximately double that from Cobham Green (at their respective optimum densities) due mainly to the later maturity of Webbs Wonderful, but also due to its higher growth rate. In an experiment carried out in England, and later in New Zealand, successive sowings (over a total period of 22 months) were sampled at regular intervals from emergence until past maturity. The dry weight per plant data were then fitted to a logistic model, with a single set of parameters for each variety over all the sowings, using chronological time, end a number of environmental time scales. All the environmental time scales tested provided a better fit than chronological time, with solar radiation being superior to 'heat units'. A further improvement with the solar radiation time scale was obtained by valueing all radiation above a certain daily integral at only 50%. In spite of the marked improvement when using environmental time scales, the results have little commercial application at present as a predictive tool because substantial differences were found in the logistic parameter estimates for the two sites, and also in the estimates of the asymptotes for the different sowings. It is essential that the asymptotes be the same over all sowings, or that the reason for any variation be known, because being based on a log. scale even a small variation would result in a large difference in absolute weight.