| 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%.;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.;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.;Sources of resistance for sorghum downy mildew, gray leaf spot, oval leaf spot, ladder spot (Cercospora fusimaculans), Acremonium wilt, and zonate leaf spot were identified by screening various international and local nurseries at several locations between 1983 and 1985. |
