FUNGAL INVASION OF KERNELS AND GRAIN MOLD DAMAGE ASSESSMENT IN DIVERSE SORGHUM GERM PLASM

Use of resistant cultivars is the most feasible way to minimize crop d amage from grain mold when sorghum (Sorghum bicolor) is grown in a cli mate conducive to fungal invasion. An experiment was conducted to asse ss relative contribution of fungal species to grain mold damage and to evaluate extent of variation in sorghum for resistance to grain mold. A large and diverse set of landraces were evaluated for grain mold re sistance at different stages of grain maturity. Fungal species infecti ng sorghum kernels were isolated and counted. Significant differences in the percentage and severity of kernel infection were observed among accessions at all stages of kernel development. The predominant funga l species isolated from sorghum kernels collected from field-grown pan icles did not change across different sampling dates and years. Althou gh visual rating identified highly susceptible accessions as early as 40 days after flowering, rating a few weeks after physiological maturi ty more reliably identified genotypes with higher levels of resistance to kernel damage. A multiple regression model involving all the funga l species isolated from sorghum kernels accounted for 64% of the varia tion in the final visual grain mold damage rating. Gibberella zeae and Fusarium moniliforme each accounted for 46 and 16%, respectively, of the variation in the final visual grain mold damage rating. Sorghum ac cessions free from colonization by one or more fungal species across t hree sampling dates were identified. Thus, it should be possible to es tablish differentials for each fungus or group of fungi to facilitate screening of germ plasm for resistance to grain mold.