Efeitos da deficiência hídrica no crescimento e desenvolvimento de dez cultivares de mandioca

Abstract

With the objective of studying the effect of water deficiency on the growth and development of ten cassava cultivars a trial was conducted in the experimental field of the Faculty of Agronomy and Forestry of Eduardo Mondlane University in 1994/1995. The trial consisted of planting cassava in black plastic bags containing soil. A completely randomized design with 5 replicates and 20 treatments (combination of 10 cultivars and 2 water levels in the bags) was used. In the first 5 weeks after planting all units were irrigated to ensure plant establishment. After this period, half of the bags were covered with black plastic to prevent rainwater from entering the bags and creating a water deficient environment for the plants. The remaining bags continued to receive daily water whenever necessary. After covering the bags (time equal to zero for the measurements), several measurements were made namely: height of each plant; central lobe length; number of formed and fallen leaves per plant, leaf longevity; date of first branching; number of apices formed per plant. At harvest, the fresh weights of the different organs per plant and the number of reserve roots per plant were determined. For each organ the weight was determined, dried in the oven. The results show that water deficiency negatively affects growth and development in all ten cultivars, although the absorbing roots showed greater development under water deficient conditions. However varietal differences were found, with cultivars that showed few differences between irrigated and non-irrigated plants, such as the cultivars Macia 1, Gangassol, Macia 2 and Munhaça in central lobe length; the cultivars Precoce D'Angola, Gangassol and Macia 2 in the number of formed leaves; the cultivars Macia 1, TMS 42025 and Gangassol in the number of fallen leaves; for cultivars H-58, Macia 1, Gangassol, Macia 2 and TMS 30395 on height growth; for cultivars Gangassol and Macia 2 on total dry weight; for cultivars Gangassol, Macia 2 and Precoce D'Angola on dry weight of the aerial part; for cultivars Macia 2, Gangassol and TMS 42025 on dry weight of the cuttings and for cultivars Gangassol and Macia 2 on dry weight of the stock roots. The cultivars Gangassol and Macia 2 were found to be adapted to water deficiency conditions by showing less reductions in the dry weight of the reserve roots (the economic part of the plant). The effect of water deficiency was not significant in the period until the first ramification in the cultivars studied. The pattern of dry matter distribution was altered in plants subjected to water deficiency when compared with irrigated plants. Plants under water stress allocated more dry matter to the absorbing roots, cuttings and stem. Dry matter accumulation in leaves was not altered when the average is considered. (TRADUÇAO NOSSA)