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Two traits in corn genotypes will be used to identify potential resistance sources: sporulation by Aspergillus flavus on intact or endosperm-wounded kernels, and accumulation of norsolorinic acid (NOR) in kernels inoculated with A. parasiticus isolate SK1.
NORis an orange-pigmented intermediate in the aflatoxin biosynthesis pathway. Genotypes that exhibit minimal sporulation and accumulation of orange pigment will be tested for aflatoxin resistance in controlled laboratory inoculations. Genotypes from this pool that prove tobe resistant will be evaluated for resistance in field trials. Those that show resistance will be examined for mechanism of resistance. Surface wax will be removed from intact kernels of these resistant genotypes, as well as standard susceptibles, and weighed. Resistant genotypes with large amounts of wax will demonstrate that wax acts as a physical barrier to infection by A. jlavus. Wax removed from kernels will be bioassayed for antifungal activity against A. jlavus. Resistant genotypes with antifungal properties will demonstrate that wax acts as a physiological barrier to infection by A. jlavus. Protein profiles determine whether proteins unique to, or in greater concentration in, resistant genotypes are involved in resistance to A. jlavus.