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

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Massey University
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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.
Broccoli, Growth