GROWTH DINAMICS AND PHYSIOLOGICAL EFFICIENCY OF ZUCCHINI PLANTS

Physiological aspects of Cucurbita pepo L., hybrid Tala, such as dinamics and aerial biomass distribution were studied at the Experimental Station of the Colegio de Postgraduados, Montecillo Texcoco, Mexico, during the 1999 and 2000 growing seasons. Four plants were sampled every two weeks during the first season, and used to measure leaf area, fresh and dry weight of leaf, stem and fruit. In the second season fruits of 18 development stages (from flowering to immature fruit) were measured every twelve hours, regarding fresh and dry weight; additionally, every seven days, fruits ranging from immature stage to physiologically mature stage, were sampled to measure fresh and dry weight. Instantaneous CO2 assimilation and transpiration rates were measured on mature leaves. The plant assigned biomass among their organs as follows, 59.4 % to leaves, 34.1 % to immature fruits and 6.38 % to stems. Plant growth showed sigmoid kinetics. Maximum leaf area occurred at 69 days after planting (dap), and immediately afterwards followed rapid defoliation. Biomass increase on reproductive organs was slow during the floral bud stage, with 0.062 g·d-1; the rate was much faster from anthesis to young fruit (“vegetable” stage), reaching 1.257 g·d-1. Maximum CO2 assimilation and minimum transpiration were registered 47 dap, 22 days before maximum leaf area (69 dap). Seed weight barely reached 2.9 % with respect to fresh fruit weight, while in dry weight it represented 32 %.