A necrose da base da fôlha do sisal

Abstract

<abstract language="eng">Sisal (Agave sisalana Perrine) growing in various localities of the State of São Paulo is often heavely damaged by "leaf basal necrose", whose symptoms are identical with the "leaf foot disease" reported from Java, East Africa and Belgian Congo. The affected leaves show in the initial stages small spots of black, slightly shrivelled tissue on the lower part of the leaf. These gradually spread out. During the later stages the affected leaves bent over at this point. Only approximately mature leaves of plants between 18 to 30 months old are affected. This disturbance was first observed in Anapolis, Araraquara and Campinas. It was thought to be due to K deficiency in the soil. In order to prove this a small fertilizer experiment was established at Campinas mainly to study the effect of potassium sulfate as a control measure for this "disease". The experiment also included calcium carbonate and control plots, each treatment being replicated three times. The results demonstrated that the trouble can be easily controled by the use ot potassium sulfate applied in the first year of cultivation (two years after planting in the nursery). At all plots not treated with K the typical black spots appeared on the leaves about one year after planting. Considerable damage was caused by this physiological disturbance in all these plots, up to 86,6% of the plants and 15,4% of all leaves being damaged at the three control plots 18 months after planting. The "leaf basal necrose" is until now the single prevalent and destructive "disease" of sisal in the State of São Paulo, where the plant is generally cultivated on K deficient soils. This explains its occurrence in almost all plantations. To avoid this disturbance sisal should be cultivated on rich soils and fertilised with K sulfate if grown on poor ones

Efeito da omissão de macronutrientes em sisal

“…Trabalhos de campo realizados por diversos pesquisadores, entre eles, DOOP (4,5), MEDINA (10), LOCK (8), COURY (3), BLACK (2) e MA-REL (9), demonstraram que dentre os distúrbios fisiológicos que ocorrem na planta de sisal por carência de um nutriente, os mais importantes são os causados pela deficiência de potássio, indicada pelo aparecimento de pequenas manchas pretas na base das folhas; mais tarde, por coalescência, as manchas invadem toda a base da folha, formando um anel preto de tecido necrosado que determina, por estrangulamento. a interrupção da circulação da seiva na folha.…”