The Role of Kernel Epicuticular Wax in Zea Mays Resistance to Aspergillus Flavus and Aflatoxin Production.

The physical and chemical roles of Zea mays (corn) kernel epicuticular wax in conferring resistance to aflatoxin production were examined. There was no evidence of a correlation between the amount of epicuticular wax and aflatoxin production in a kernel development experiment. Aflatoxin levels decreased as kernels developed. Epicuticular wax removal reduced aflatoxin at the earlier stages of development but increased aflatoxin in some genotypes at the later stages, indicating the importance of epicuticular wax during late-stage development and hinting of different defense mechanisms between the early- and late-stage kernels. The amount of epicuticular wax from mature kernels of 23 commercial hybrids and the aflatoxin resistant GT-MAS:gk genotype was compared with aflatoxin production in wax-extracted and non-wax-extracted kernels. Unextracted GT-MAS:gk kernels produced the lowest aflatoxin in a kernel screening assay but ranked fourth in weight of extracted wax per seed. Data from all 24 genotypes in the regression test resulted in an r-square value of 0.042 (positive correlation) and of 0.0325 (negative correlation) between amount of wax per seed and aflatoxin in wax extracted and non-wax-extracted kernels, respectively. Regression analysis for a selected group of 16 genotypes produced r-square values of 0.1528 and 0.5659 for wax-extracted and non-wax-extracted kernels, respectively, indicating a decrease in aflatoxin with increasing extractable wax. Epicuticular wax analysis indicated alkanes of odd numbered chain lengths C27, C29, and C31, predominated in all genotypes at all stages of development. However, sterol analysis indicated quantitative differences between resistant and susceptible genotypes. Epicuticular wax profiles for resistant genotypes showed differences in epicuticular wax for each genotype. Four chemical components were detectable exclusively in the resistant genotypes. A thin layer chromatography plate bioassay showed antifungal spots in waxes from Pioneer 3154 and T115. Fatty acid analysis of GT-MAS:gk and those of 13 commercial hybrids showed that epicuticular wax of GT-MAS:gk was the most different. This study represents the first report of epicuticular wax accumulation and aflatoxin production during kernel development.