Tissue-specific components of resistance to Aspergillus ear rot of maize.

Aspergillus flavus and other Aspergillus spp. infect maize and produce aflatoxins. An important control measure is the use of resistant maize hybrids. There are several reports of maize lines that are resistant to aflatoxin accumulation but the mechanisms of resistance remain unknown. To gain a better understanding of resistance, we dissected the phenotype into 10 components: 4 pertaining to the response of silk, 4 pertaining to the response of developing kernels, and 2 pertaining to the response of mature kernels to inoculation with A. flavus. In order to challenge different tissues and to evaluate multiple components of resistance, various inoculation methods were used in experiments in vitro and under field conditions on a panel of diverse maize inbred lines over 3 years. As is typical for this trait, significant genotype-environment interactions were found for all the components of resistance studied. There was, however, significant variation in maize germplasm for susceptibility to silk and kernel colonization by A. flavus as measured in field assays. Resistance to silk colonization has not previously been reported. A significant correlation of resistance to aflatoxin accumulation with flowering time and kernel composition traits (fiber, ash, carbohydrate, and seed weight) was detected. In addition, correlation analyses with data available in the literature indicated that lines that flower later in the season tend to be more resistant. We were not able to demonstrate that components identified in vitro were associated with reduced aflatoxin accumulation in the field.