Manejo agroecológico da cultura do inhame: produtividade, qualidade, controle de nematóides e manchas foliares

Abstract

Agroecology is based on the preservation and increase of agroecossystems biodiversity, which constitutes the base to achieve sustentability. The yam (Dioscorea cayennensis Lam.) crop has been pointed out in the Northeastern region of Brazil, as a promising crop for small and average farmers. This work had the objective of evaluating agroecological management of yam plantations, with the utilization of green manure, and its effect on the productive characteristics, in the financial return index, and in the major diseases associated with this crop. Tree experiments were carried out with the following leguminous plants as green manure: crotalaria (Crotalaria juncea) (CJ), pigeon pea (Cajanus cajan) (CC), and the combination of both (CJ + CC). Under in vitro conditions, the first experiment evaluated the nematostactic and nematicide effect of extracts from fresh and dry matter of aerial part of CJ, CC, and CJ + CC. The second experiment was carried out under greenhouse conditions, to evaluate the effect of soil incorporation of CJ, CC, and CJ + CC in the infectivity of Scutellonema bradys, using tomato plants as the host plant. The third experiment was carried out in the field, to evaluate the effect of intercropping and incorporation of CJ, CC, and CJ + CC to soil, in the quality, yield, financial return index, management of yam parasitic nematodes, and severity of leaf spots. The extracts from fresh matter of CJ and CC presented a nematicide effect of 100% and 40% to S. bradys, respectively. Soil incorporation of CJ inhibited the infectivity of S. bradys in tomato seedlings. Planting CJ and CJ + CC between the yam planting lines, was shown to be an effective method for the management of S. bradys and Rotylenchulus reniformis. The yam crop system with CC between the yam planting lines promoted the highest total tuber yield (33.13 t/ha), yield of tubers with quality for exportation (22.96 t/ha), commercial tubers (32.24 t/ha), and the highest operational profit (US$5,707.88). Logistic was the model that best described the progress of yam leaf spot, for the Recôncavo region of Bahia. Rates of disease progress were similar for the crop systems with green manure. The conventional crop system presented a disease progression index of 37 % superior to that of the green manure crop systems. A low correlation was observed between the area under the disease progress curves for the leaf spot caused by C. eragrostidis, Phyllosticta sp., and the combination of leaf spots caused by both pathogens, with regard to the yam tuber weight, diameter, and length.