A study of sorghum diseases in Honduras, their importance under different cropping systems, and strategies for their control

Typescript (photocopy).Twenty-one sorghum diseases were identified in different sorghum-growing regions of Honduras, of which eight were studied with regard to their effect on sorghum yield. Sorghum downy mildew, caused by Peronosclerospora sorghi, was studied by comparing three near-isogenic populations (resistant, intermediate, and susceptible), planted in a disease-free site and in the presence of the disease. A 52% incidence of downy mildew reduced yields by 46%. Paired comparisons of diseased and healthy plants showed that maize dwarf mosaic, an aphid-transmitted virus disease, caused a 52% yield reduction on traditional land race cultivars. The same technique was used to study the effect of Acremonium wilt, caused by Acremonium strictum, which caused a 36% yield reduction on a susceptible cultivar (BTX623), and a 33% yield loss on land race cultivars. A holistic, multivariate study, carried out in subsistence farmers' fields, produced a multiple regression model for estimating sorghum yields based on plant height, panicle length, and disease severity data. Using this model, a 14.6% yield reduction was estimated to be caused by gray leaf spot (Cercospora sorghi), based on severity levels observed in farmers' fields. Rust (Puccinia purpurea) was estimated to cause a 3.5% yield reduction, and oval leaf spot (Ramulispora sorghicola) reduced yields by 5.5%. In controlled experiments using fungicide-protected and unprotected plots, zonate leaf spot (Gloeocercospora sorghi) caused a 15% yield reduction. Gray leaf spot, in a similar trial, reduced yields by 13.5% on the most popular improved cultivar (Tortillero). When cropping systems were compared, sorghum-maize was found to have a lower oval leaf spot severity than sorghum alone, but the maize dwarf mosaic incidence was higher. Early planting resulted in higher disease severities than late planting of photoperiod-sensitive land race cultivars. Improved cultivars had fewer diseases, but higher severities, than land race cultivars when both were planted in the late planting season in August. Sorghum-pigeon pea intercropping increased gray leaf spot severity, as compared to sorghum alone. Sorghum-bean intercropping did not affect sorghum disease severities, or yields..