Bean production constraints, bean seed quality and effect of intercropping on floury leaf spot disease and yields in Taita Taveta District, Kenya
T he study was undertaken to document bean production constraints in Taita-Taveta district, to evaluate the incidence and severity of lloury leaf spot (Mycovellosiella pluiseoli (Drummond) Deighton) on different bean lines and the resulting yields when grown in monoculture and as an intercrop with maize and to assess the effect of storage period on bean seed quality. A Participatory Rural Appraisal was conducted in the area followed by administration of a semi-structured questionnaire. Four and five bean lines in farmer-managed and re scare her-managed trials respectively were planted as nionocrop (at two varying spacing) and intercrops (at two varying spacing) with maize. Bean seeds produced from the farmer-managed trials were assessed for quality after 2 and 5 months of storage. The key bean production constraints in order of importance were insect pests, high cost of chemicals, diseases, high cost of certified seed, lack of high quality seed at farm level for planting and poor soil fertility. In farmer-managed trials, intercropping beans with maize increased the incidence of floury leaf spot during the short rains of 1999. The highest (82.1%) incidence was observed on bean line M22 planted with maize and sown at a spacing of 15 cm x 40 cm whereas the lowest (8.9%) incidence was observed on bean line H8 planted alone at a spacing of 15 cm x 80 cm.Seed quality tests revealed a significant (P=0.05) decrease in germination percentage in all seed lots after 5 months of storage. There was an increase in the electrical conductivity in all seed lots, a decrease in the Tetrazolium chloride staining in all seed lots and an increase in the moisture content in some seed lots following 5 months of storage. In researcher-managed trials, intercropping beans with maize had no effect on the incidence but increased floury leaf spot severity. During the long and the residual rains of 2000, the highest severity levels of 14.8% and 1.9% were observed at 10 weeks after planting on bean line M22 planted with maize and sown at a spacing of 15 cm x 40 cm. Bean yields were higher in the monocrop system than in the intercrop system. The best (1517.5 kg/ha) yields during the long rains were produced by bean line E8 planted as a monocrop at a spacing of 15 cm x 50 cm whereas the lowest (410.7 kg/ha) yields were observed on bean line No.B planted with maize and sown at a spacing of 15 cm x 80 cm. The results indicated that intercropping maize with beans had no effect on incidence but increased the severity of floury leaf spot. Additionally, intercropping resulted in reduction of bean yields probably due to reduced bean plant population and competition from maize. It was also evident that the quality of bean seeds decreased with increased time in storage but the decrease varied among seed lots.
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