Field-damaged peanuts

The evidence clearly supports the hypothesis that stilbene phytoalexins in peanuts are an important natural bioregulator of preharvest aflatoxin contamination. That evidence includes the facts that (1) stilbenes are naturally produced in field-damaged peanuts (2) stilbenes possess biological activity against A, flavus and A. parasiticus and (3) although invasion of peanuts by A. flavus and A. parasiticus can occur under any conditions, aflatoxin contamination does not occur until peanuts lose the capacity for phytoalexin production as a result of drought-induced kernel dehydration. 

An important field study conducted at various sites throughout the United States involved the exposure of crop plants to either ambient air at each site, or to a typical background ozone concentration of 25 ppb. Symptoms of acute ozone injuries were observed at all five of the study sites, although the damages were more frequent and severe in the southwest. On average, it was estimated that exposures to ambient ozone concentrations caused yield decreases of about 53-56% in lettuce, 14-17% in peanut, 10% in soybean, and 7% in turnip. Overall, it has been estimated that ozone causes crop losses equivalent to 2-4% of the potential yield in the United States, resulting in 3 billion in agricultural losses each year. 

Therefore, the fact that peanuts produce stilbene phytoalexins naturally in response to damage in the field but do not become contaminated with aflatoxin (indicative of A. flavus growth) until subjected to prolonged drought stress points toward a presumptive role for these compounds in the natural bioregulation of aflatoxin contamination. 

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