Seed Health Management for Better Productivity - Govind Ballabh ...

(Seed Health Management for Better Productivity)aflatoxin but a derivative of kojic acid, another relatively unique fungal metabolite. Bright greenishyellowfluorescence in maize kernels was adapted as a presumptive test for presence of fungi inthe A. flavus group.Sixty ears from each of 60 fields in a four-country area of southeastern Missouri, 600 earsfrom two Missouri field and 750 ears from five fields in southern Illinois were collected. Mycologicalstudies of kernels demonstrated an average A. flavus incidence of about 5%, with elevatedoccurrence in kernels from insect damaged ears. Although earlier reports had identified thepresence of A. flavus in preharvest maize, the 5% incidence exceeded prior observations.Morphological tests identified elevated occurrence of A. flavus relative to A. parasiticus in kernelsand insects. After shelling, drying and cracking, 237 samples of the 3600 ears in the generalsurvey and 12 of 1350 ears in the intensive study exhibited BGY fluorescence. Aflatoxin testsshowed that 120/3600 in the general survey and 6/1350 in the intensive study contained aflatoxinlevels exceeding 20 ppb.A number of facts concerning the preharvest contamination process had been established asbelow:• Yellow and white maize were equivalent in susceptibility to fungal infection;• A positive relationship was obwerved between BGY-fluorescing particles and presence ofaflatoxin;• Aflatoxin contamination varied both intra-and inter regional;• Aspergillus flavus predominated in aflatoxin-contaminated maize kernels and associatedinsects;• Kernel damage by insects increased the potential for aflatoxin accumulation;• Intensive insecticide application reduced but did not eliminate preharvest toxin production;• Aspergillus flavus infection occurred from two weeks after flowering to physiologicalmaturity, with maximum infection in the late-milk to early-dough stage (20 days postflowering);• Variation in timing of maize maturation appeared to be linked to contamination;• Stress factors during crop development seemed to incrase susceptibility; and• Genotypic determinants, such as enhanced husk development, were linked to reducedpreharvest aflatoxin contamination.Preharvest moistureMoisture was a major factor among many that affected the contamination process.Although the xerotolerance of A. flavus provided and opportunity for competitive development atmoistures between 17 and 22%, it was apparent that the fungus was infecting kernels at 50%moisture and above. To examine the moisture-related factors of preharvest toxin contamination,an interregional study was carried out in maize grown in Illinois, Missouri and Georgia. The resultsdemonstrated that early aflatoxin contamination occurred in three diverse environments, butmoisture levels did not appear to independently exert a controlling influence in the process.- 135 -