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    The effect of plant density, cultivar and season on the growth and development of broccoli : a thesis presented in partial fulfilment of the requirements for the degree of Master in Horticultural Science (Vegetable Production) at Massey University
    (Massey University, 1995) Pinera, Danilo R
    Two field trials (summer and winter) were conducted at the Plant Growth Unit (PGU) to investigate the effects of density and season of planting on different cultivars of broccoli. Different aspects of growth and development were studied including dry matter accumulation, leaf production, curd initiation and curd maturity. Polynomial regression equations were fitted to the primary data and resulted in typical growth curves from which growth analysis parameters were derived. The season of planting significantly effected the developmental stages of the crop. RGR calculated according to the functional approach declined linearly with time in both winter and summer trial. It was initially highest in the summer trial but declined much faster than in winter trial. One of the components of RGR, namely LAR also showed the reduction over time, in both summer and winter plantings. The other component, NAR decline with time in summer, but showed slight increase over time in the winter trial. LAR was consistently lower during the summer trial compared with the winter trial. This consistent reduction is associated mainly with a lower specific leaf weight (SLW) because plants have thicker leaves which may absorb more radiation and therefore be more efficient in dry matter production. Differences in growth between seasons can be explained primarily by differences in accumulated heat units. In this study, it was evident that the number of leaves produced varied with planting season. The higher the temperature regime the more leaves produced hence, leaf count per plant was slightly higher in the summer than during the winter season. The time of head initiation were affected by planting density for both season. In the summer planting, widely spaced plants had higher leaf areas, number of leaves produced and curd yield but in the winter planting showed no significant differences in the number of leaves produced and the curd weight per plant between densities. The final number of leaves at initiation time showed variations with season of planting which suggests that leaf number can be useful index for the morphological age of the plant at curd initiation stage. Curd initiation (an important developmental event) was found to be strongly influenced by temperature. The number of days from transplanting to curd initiation was shorter in summer and longer in winter season. Considering a normal time scale, variations in the number of days from planting to curd initiation until maturity for both season was influenced by the two developmental stages of the crop: 1) planting to curd initiation, 2) curd initiation up to maturity. It took almost twice as long period for the plant to initiate curd during winter than during summer and the time from curd initiation to maturity was longest during the winter. The potential of the plants to produce dry matter varied with season. Total dry matter production was considerably lower in the winter crop which strongly suggests that the lower the temperature regime, the lower the potential for dry matter production. The heat unit accumulation necessary to bring the crop to the same stage of maturity varied in such a manner that it was lower when the season was cool, and higher when the season was warm. Total biomass per unit area increased with later harvests in the summer planting. Density influenced the curd and total dry weight per plant only in the summer planting. Varietal differences were found for both season of planting. Cultivar Shogun, with the longer growing period, had the lowest dry weight per plant for both plantings.
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    Effectiveness of UV-C irradiation on controlling growth of L. monocytogenes on fresh cut broccoli : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, New Zealand
    (Massey University, 2015) Gamage, Gayani
    Increasing numbers of foodborne disease outbreaks related to fresh produce are reported every year from around the world. This increase is partly attributed to increased consumption of fresh produce such as whole and fresh cut fruits and vegetables. Fresh produce can be contaminated at any time from field to table, providing channels for transmitting foodborne pathogens to humans. Studies have reported that human pathogens such as Listeria monocytogenes, which can grow and survive under refrigerated conditions, cannot be adequately removed by washing with commonly used chemical disinfectants. Consumers prefer products that have not been treated chemically, especially fresh products that are consumed without further processing before consumption. Physical treatments such as UV-C irradiation have shown promising effects in improving storage life, nutritional quality, and microbial safety of fresh produce. UV-C irradiation is beneficial due to its direct germicidal effect, and could possibly induce defence responses in fresh produce which may further improve quality and safety. However, direct germicidal effects would be limited by the uneven surfaces of fresh produce, with risk of survival of pathogens in areas shaded from direct UV exposure. It is also not clear whether induced defence related changes would be sufficient to offer any significant protection against human pathogens. Therefore, this study focused on evaluating the efficacy of postharvest UV-C irradiation to control growth of L. monocytogenes inoculated onto fresh cut broccoli at different times after UV-C treatment, and possible mechanisms of induced resistance. UV-C irradiation supplied at a total dose of 5.2 kJ m-2 significantly reduced growth of L. monocytogenes inoculated onto fresh cut broccoli 6 h and 24 h after treatment, whereas a 2.6 kJ m-2 treatment was suppressive only 24 h after treatment. Neither dose of UV-C adversely affected the quality of fresh cut broccoli compared to untreated broccoli. The in vitro study of extracts of UV-C treated broccoli extracted 24 h after UV-C treatment showed that certain extracts were indeed suppressive against L. monocytogenes. Aqueous extract of UV-C treated broccoli extracted 24 h after treatment suppressed growth of L. monocytogenes compared to extracts of untreated broccoli. Phytochemical analysis of broccoli extracts by LC-HRMS revealed that UV-C irradiation significantly increased production of particular phytochemical compounds. Compound identifications included raphanusamic acid, salicylic acid-ß-glucoside, p-coumaryl quinic acid, all of which have been previously reported as being involved in plant defence. Therefore, UV-C irradiation appears to induce defence responses which may be effective systemically, and therefore not critically dependent on achieving an effective sanitising dose of UV-C across the entire broccoli surface. This may alleviate concerns about relying on uniform illumination for anticipated benefits. Overall, these results suggest that treatment of broccoli with UV-C irradiation should lead to immediate microbial mortality, and a longer-lasting induction of defence systems in the tissues, which would suppress growth of pathogens such as L. monocytogenes if the tissue became contaminated during processing. Therefore this treatment can be recommended as a hurdle technology to improve microbial safety of packaged fresh produce.
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    Transplanting studies with processing tomato (Lycopersicon esculentum Mill.) and green sprouting broccoli (Brassica oleracea L. var. italica Plenck) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticulture at Massey University
    (Massey University, 1992) Davis, Stuart Ian
    Field experiments were conducted to evaluate the performance of module-raised and bare-root seedling transplants of determinate tomato and green sprouting broccoli. In the tomato experiment, seedlings raised in 36 cm3 modules in a greenhouse and bare-root transplants raised in a seed-bed under cold frames were transplanted into a field at Hastings in October 1983. In the broccoli study, seedlings were raised in 36 cm3 modules and in seed-beds in a field and in a greenhouse and then transplanted into a field at Massey University in November 1984. Tomato plants established as module-raised transplants had higher shoot and root dry weights 35 days after transplanting, and flowered 2 weeks earlier than plants established as bare-root transplants. A series of nine destructive harvests, at approximately weekly intervals, revealed similar patterns of red fruit yield with time for plants established from the two types of transplant. The loss of the early growth advantage of the plants established from module-raised transplants was not explained by conversion to a thermal time scale. Further research is required to determine if the sharp peak of red fruit yield with time recorded in this experiment is typical for tomato crops grown in New Zealand. The growth of broccoli plants over the first 32 days from transplanting was recorded from unreplicated plots. From the results of a series of dry weight harvests, it was estimated that, 18 days after transplanting, broccoli plants established as module-raised transplants produced in the field and in the greenhouse were 7 and 5 days, respectively, more advanced in terms of shoot dry weight than plants established from the corresponding bare-root treatments. Plants established from module-raised transplants initiated terminal inflorescences earlier than plants established from the corresponding bare-root transplants. These results were attributed to reduced root disturbance at transplanting for the module-raised transplants. The effects of transplant type on the maturity and yield of broccoli were evaluated using a series of selective harvests in a replicated experiment. In the case of the field-raised transplants, the more rapid establishment and earlier initiation of the terminal head of plants established from module-raised transplants was reflected in earlier maturity at harvest. There was no difference in the time to maturity of module-raised and bare-root transplants raised in the greenhouse. The patterns of post-transplanting growth and maturity of plants raised in modules in the greenhouse and transplanted with or without growing medium around the roots were very similar. This indicated that reduced root disturbance was a more important factor in the rapid establishment of module-raised transplants than the presence of a reserve of water in the growing medium of the module. These results with tomato and broccoli illustrate that earlier and more uniform establishment of module-raised transplants may not always be reflected in earlier and more uniform crop maturity, due to the effects of environmental factors and inter-plant competition later in the growth of the crop. It is suggested that differences in crop maturity and yield between plants established from module-raised and bare-root transplants would have been more marked under more stressful field establishment conditions.
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    Growth and development studies with broccoli (Brassica oleraceae var. italica) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Horticulture at Massey University
    (Massey University, 1989) Diputado, Misael T
    The influence of temperature on the growth and development of broccoli was studied in the field, the greenhouse and in controlled climate experiments at Massey University in 1985-88. In the field experiment, 6 sowings at 2-month intervals of four cultivars of broccoli were made. The effect of temperature on a number of growth and development parameters of the plant was assessed using the heat unit system. The greenhouse and controlled climate experiments were conducted as follow-up studies to determine the independent effect of temperature on the development, growth, maturity characteristics and curd quality of broccoli. In all the studies, growth analysis using the functional approach was employed. Temperature, through the use of the heat unit system, was found to account for a major proportion of the variation between sowing dates in the rate of dry matter accumulation, rate of leaf production, times to curd initiation and maturity, and rate of curd growth. Dry matter accumulation could be expressed as a logistic function of heat unit summation (HUS) above a base temperature of 3C; rate of leaf production, a linear function of HUS above -2C; and curd growth (increase in curd diameter), as a quadratic function of HUS above 3C. Time to curd initiation expressed as number of heat units was calculated above a base temperature of 0C. The varietal constants (total HUS from sowing to curd maturity) were calculated to be 1188, 1123, 1217 and 1347 heat units for Premium Crop, Mercedes, Idol and Fordhook Late, respectively. The final number of leaves did not vary with sowing date but varied among the cultivars and was related to the time to curd initiation. The longer the time to curd initiation, the more leaves were formed. The economic yield varied with sowing date and was related mainly to differences in total dry matter accumulation potential. With the cultivars, the harvest index was equally important. Differences in total dry matter accumulation between cultivars were not closely linked to differences in the relative growth rate (RGR) or any growth parameter, but were related more to the growth duration. There was some indication of a relationship between harvest index and net assimilation rate (NAR) at curd initiation time. NAR was found to be inversely related to the specific leaf weight (SLW) which is indicative of the thickness of the leaves. High temperature regime (30C) reduced the RGR and NAR of plants relative to a 20C regime. It did not affect rate of leaf production and did not prevent or delay curd initiation. When imposed before the curd initiation stage 1-week exposure to high temperature did not reduce curd quality. When imposed at the early or late curd development stages it reduced curd quality with the reduction being more pronounced at the latter stage. When treatment exposure was increased to two weeks similar results were obtained. Growing the plants under continuous high temperature caused a range of curd morphological abnormalities such as the presence of bracts throughout the surface of the curd, suppression of the growth of the buds or irregular elongation of curd internodes.
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    Role of cytokinin and ethylene during senescence in broccoli (Brassica oleracea var. Italica) : a thesis submitted for the degree of Doctor of Philosophy at Massey University
    (Massey University, 2003) Gapper, Nigel Esteven
    Broccoli (Brassica oleracea var. italica) deteriorates rapidly following harvest. The two plant hormones ethylene and cytokinin are known to act antagonistically on harvest-induced senescence in broccoli: ethylene acts by accelerating the process, whereas additional cytokinin delays it. The overall aim of this thesis was to gain a better understanding of how these two hormones control postharvest senescence. The effects of exogenous cytokinin (6-benzyl aminopurine, 6-BAP), 1-aminocyclopropane-1-carboxylic acid (ACC) and sucrose on senescence-associated gene expression were measured in both wild-type plants and transgenic plants harbouring an antisense tomato ACC oxidase gene (pTOM13). Exogenous cytokinin caused both a reduction (BoACO) and an increase (BoACS) in ethylene biosynthetic gene expression as well as reduced expression of genes encoding sucrose transporters and carbohydrate metabolising enzymes, indicating a significant role for cytokinin in the delay of senescence. Transgenic broccoli was produced using Agrobacterium tumefaciens-mediated transformation. Ethylene biosynthesis was targeted via an antisense BoACO2 gene fused to the harvest-induced asparagine synthetase (AS) promoter from asparagus. In addition, broccoli was transformed with constructs harbouring the Agrobacterium tumefaciens isopentenyl transferase (ipt) gene using the senescence-associated SAG12 and floral-associated MYB305 gene promoters to enhance the levels of cytokinin either during senescence or in floral tissue, respectively. The presence of the antisense AS-ACO construct was associated with an increased rate of transformation when compared to control constructs. Physiological analyses of mature plants showed that the antisense AS-ACO gene construct caused delayed senescence in both detached leaves and detached heads. Gene expression analyses of harvested floret tissue from AS-ACO lines showed decreases in transcript levels of senescence marker genes compared to wild-type and transgenic control lines, as well as a reduction in expression of sucrose transporter and carbohydrate metabolising genes, confirming the key role of ethylene in the promotion of senescence. In addition, genes involved with cytokinin biosynthesis and metabolism were isolated by PCR using primers based on Arabidopsis clones. The four broccoli ipt sequences aligned closely to four of the Arabidopsis sequences and were subsequently named BoIPT4, BoIPT5, BoIPT6 and BoIPT7. A cytokinin oxidase clone (BoCKX) was also isolated from broccoli. The four BoIPT genes were expressed in a number of different tissues, suggesting that the different genes may be involved in different biological processes in the plant. BoIPT4 was expressed early and BoCKX expressed late in florets during senescence. A model depicting the regulation of senescence in broccoli through the expression of cytokinin biosynthesis and metabolism genes, and their interaction with ethylene and carbohydrate metabolism is presented and discussed.