Fungal Invasion of Kernels and Grain Mold Damage Assessment in Diverse Sorghum Germ Plasm

Abstract

Use of resistant cultivars is the most feasible way to minimize crop damage from grain mold when sorghum (Sorghum bicolor) is grown in a climate conducive to fungal invasion. An experiment was conducted to assess 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 resistance at different stages of grain maturity. Fungal species infecting 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 fungal species isolated from sorghum kernels collected from field-grown panicles did not change across different sampling dates and years. Although visual rating identified highly susceptible accessions as early as 40 days after flowering, rating a few weeks after physiological maturity more reliably identified genotypes with higher levels of resistance to kernel damage. A multiple regression model involving all the fungal species isolated from sorghum kernels accounted for 64% of the variation 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 accessions free from colonization by one or more fungal species across three sampling dates were identified. Thus, it should be possible to establish differentials for each fungus or group of fungi to facilitate screening of germ plasm for resistance to grain mold.