Control of Leaf Spot Diseases on Ecotypes of Faba Bean (<i>Vicia faba</i> L.) Produced in the Andean Region of Bolivia

Abstract

The basin of Lake Titicaca is a faba bean-producing microregion of Bolivia where the crop is destined for export. The most commonly cultivated ecotypes “Gigante de Copacabana” and “Usnayo” are affected by diseases that can cause production losses. The aims of the present work were to identify the causal agents of leaf spot affecting these ecotypes, to record disease intensity levels, and to estimate their effect on production. In 2004 and 2005, leaflet, stem and pod samples were taken from faba bean plants with leaf spot growing in the Lake Titicaca area, and from plants in an experimental plot established to determine the effect of five different treatments on production and disease intensity: T1 = Control; T2 = seed treatment with Trichoderma sp. + alternate foliar spraying with benomyl and mancozeb; T3 = seed treatment with fludioxanil/metalaxyl M + alternate foliar spraying with benomyl and mancozeb; T4 = foliar spraying with Trichoderma sp.; T5 = alternate foliar spraying with cymoxanyl and mancozeb-chlorothalonil. Microscopic analysis of the samples revealed the presence of new fungal pathogens for faba beans in Bolivia (Cladosporium sp., and Lepthosphaerulina sp.) as well as emerging fungal pathogens (Botrytis cinerea, B. fabae, Ascochyta fabae, Alternaria sp. and Cercospora sp.). None of the treatments affected the disease progression curve (DPC) for incidence, although effects were seen with respect to disease severity. The seed + foliar treatments (T2 and T3) were more effective at controlling disease than leaf treatments on their own (T4 and T5). Modelling analysis showed faba bean leaf spot disease to be moderately destructive. Compared to chemical treatments, biocontrol with Trichoderma spp. preliminary was found to provide good control of the disease. Losses due to leaf spot disease of 36% were recorded, and a strong correlation detected between yield and disease severity.