GROWTH OF AN ASPERGILLUS-FLAVUS TRANSFORMANT EXPRESSING ESCHERICHIA-COLI BETA-GLUCURONIDASE IN MAIZE KERNELS RESISTANT TO AFLATOXIN PRODUCTION

Kernels of a maize inbred that demonstrated resistance to aflatoxin pr oduction in previous studies were inoculated with an Aspergillus flavu s strain containing the Escherichia coli beta-D-glucuronidase reporter gene linked to a beta-tubulin gene promoter and assessed for both fun gal growth and aflatoxin accumulation. Prior to inoculation, kernels w ere pin-wounded through the pericarp to the endosperm, pin-wounded in the embryo region, or left unwounded. After 7 days incubation with the fungus, beta-glucuronidase activity (fungal growth) in the kernels wa s quantified using a fluorogenic assay and aflatoxin B-1 content of th e same kernels was analyzed. Kernels of a susceptible inbred, similarl y treated, served as controls. Results indicate a positive relationshi p between aflatoxin levels and the amount of fungal growth. However, r esistant kernels wounded through the pericarp to the endosperm before inoculation supported an increase in aflatoxin B-1 over levels observe d in nonwounded kernels, without an increase in fungal growth. Woundin g kernels of the resistant inbred through the embryo resulted in both the greatest fungal growth and the highest levels of aflatoxin B-1 for this genotype. Maintenance of resistance to aflatoxin BI in endosperm -wounded kernels may be due to the action of a mechanism which Limits fungal access to the kernel embryo.