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 evalu ated at West Lafayette, IN, over three crop seasons (1989, 1990, and 1 992) to assess changes in phenolic compounds during seed development a nd how these changes influence grain molding. Samples were collected f or 9 weeks at 7-day intervals starting 7 days after anthesis. Acidifie d methanol extracts of the seeds were assayed to determine concentrati ons of 3-deoxyanthocyanidins, flavan-4-ols, and proanthocyanidins. See ds were also plated on biological media to observe the level of seed i nfection by mold-causing fungi. Flavan-4-ol concentrations were high a nd similar for both the mold-resistant-and mold-susceptible genotypes at-early stages of seed development. In susceptible genotypes, the fla van-4-ol concentration dropped by 67% between the third and the last s ampling dates compared with a 20% decline for the resistant genotypes in the same period. In addition, the resistant genotypes (P954255, P93 2062, IS15346, IS7822, P013931) had high concentrations of proanthocya nidins throughout the season compared with susceptible lines, which la cked or had negligible amounts of this material. Although significant differences occurred among genotypes for 3-deoxyanthocyanidins, the pr esence of these pigments did not differentiate mold-resistant-and mold -susceptible genotypes. The results also showed that the highest incid ence of seed infection by fungi occurred between 25 and 35 days after anthesis. Alternaria, Fusarium (especially F. moniliforme), Cladospori um, and Epicoccum species were the major fungi isolated from the seeds .