RESISTANCE TO AFLATOXIN CONTAMINATION IN CORN AS INFLUENCED BY RELATIVE-HUMIDITY AND KERNEL GERMINATION

Kernels of corn population GT-MAS:gk, resistant to aflatoxin B-1 produ ction by Aspergillus flavus, and susceptible Pioneer hybrid 3154 were tested for aflatoxin when incubated under different relative humiditie s (RH). High aflatoxin levels were not detected in either genotype at RH < 91%. Resistance in GT-MAS:gk was consistent across all RH levels (91 to 100%) at which significant aflatoxin accumulation was detected. Aflatoxin levels in GT-MAS:gk averaged about 98% less than those in s usceptible Pioneer 3154, which suggests that storage of this or other genotypes with similar resistance mechanisms may be possible under moi sture conditions less exacting than are required with susceptible hybr ids. Results for fungus,growth and sporulation ratings on kernel surfa ces were similar to those for aflatoxin levels. When kernels of both g enotypes were preincubated 3 days at 100% RH prior to inoculation with A. flavus, germination percentages increased to very high levels comp ared to those of kernels that were not preincubated. In preincubated k ernels aflatoxin levels remained consistently low in GT-MAS:gk but dec reased markedly (61%) in Pioneer 3154. When eight susceptible hybrids were evaluated for aflatoxin accumulation in preincubated kernels, sev en of these supported significantly lower toxin levels than kernels no t subjected to preincubation. Average reduction across hybrids was 83% , and reductions within hybrids ranged from 68 to 96%. Preincubated ke rnels of one susceptible hybrid (Deltapine G-4666) supported aflatoxin levels comparable to those in resistant GT-MAS:gk. Data suggest that an inhibitor of aflatoxin biosynthesis may be induced during kernel ge rmination. Possible mechanisms for embryo effects on resistance to afl atoxin accumulation are discussed.