Grain Mold Resistance and Polyphenol Accumulation in Sorghum

Ten sorghum [Sorghum bicolor (L) Moench] genotypes with differences in phenolic compound concentrations and grain mold resistance were evaluated at West Lafayette, IN, over three crop seasons (1989, 1990, and 1992) to assess changes in phenolic compounds during seed development and how these changes influence grain molding. Samples were collected for 9 weeks at 7-day intervals starting 7 days after anthesis. Acidified methanol extracts of the seeds were assayed to determine concentrations of 3-deoxyanthocyanidins, flavan-4-ols, and proanthocyanidins. Seeds were also plated on biological media to observe the level of seed infection by mold-causing fungi. Flavan-4-ol concentrations were high and similar for both the mold-resistant and mold-susceptible genotypes at early stages of seed development. In susceptible genotypes, the flavan-4-ol concentration dropped by 67% between the third and the last sampling dates compared with a 20% decline for the resistant genotypes in the same period. In addition, the resistant genotypes (P954255, P932062, IS15346, IS7822, P013931) had high concentrations of proanthocyanidins throughout the season compared with susceptible lines, which lacked or had negligible amounts of this material. Although significant differences occurred among genotypes for 3-deoxyanthocyanidins, the presence of these pigments did not differentiate mold-resistant and mold-susceptible genotypes. The results also showed that the highest incidence of seed infection by fungi occurred between 25 and 35 days after anthesis. Alternaria, Fusarium (especially F. moniliforme), Cladosporium, and Epicoccum species were the major fungi isolated from the seeds. Keywords: Sorghum; polyphenol; 3-deoxyanthocyanidin; flavan-4-ols; proanthocyanidin; apigeninidin; luteolinidin; grain mold