Submitted to: World Mycotoxin Forum, the Third Conference
Publication Type: Abstract Only
Publication Acceptance Date: November 6, 2006
Publication Date: N/A
Interpretive Summary: None required.
Technical Abstract: Most of the pathogens that attack peanut (Arachis hypogaea L.) are of fungal origin. Aspergillus flavus and A. parasiticus invade peanuts and subsequently lead to their contamination with carcinogenic aflatoxins. Preharvest aflatoxin contamination makes peanuts unsafe for consumption and is a major economic problem for peanut industries worldwide. Peanuts can naturally resist fungal growth when provided with adequate moisture throughout the growing season. The mechanism of resistance to fungal infection has been reported as the capacity to synthesize stilbene phytoalexins, which are antibiotic, low molecular weight metabolites. Research on peanut resistance to aflatoxin contamination under natural field conditions, such as drought stress and pest damage, may help outline measurable chemical factors that could be used in new programs for breeding resistant peanut cultivars. The objective of this research was to study the relationship between phytoalexin production and aflatoxin contamination in commercial peanut cultivars as influenced by insect damage and drought stress in the field. A two-year field study of the aflatoxin-phytoalexin interrelationship in disease-resistant and susceptible peanut genotypes was performed. Five genotypes (Georgia Green, Tifton 8, C-99R, GK-7 High Oleic, and MARC I) differing in resistance to preharvest aflatoxin contamination and major peanut diseases were investigated for their ability to produce phytoalexins under normal and drought field conditions; drought is the major factor leading to preharvest aflatoxin contamination. Known major phytoalexins were quantitated in peanuts of different pod maturity (yellow, orange, brown, and black) without or with insect pod damage (externally scarified and penetrated). Comparison of Georgia Green (with small root system) and Tifton 8 (with large root system) showed that pods of the Tifton 8 genotype had higher water activity under drought stress. Damaged pods of Tifton 8 produced significantly higher levels of phytoalexins compared with Georgia Green. Insect damage of pods increased total aflatoxin contamination in both genotypes. However, Tifton 8 had significantly lower aflatoxin contamination in penetrated pods, which was associated with its ability to synthesize phytoalexins. Insect-damaged pods of C-99R and Tifton 8 genotypes had significantly higher concentrations of phytoalexins than other genotypes. The same genotypes were the most resistant to Tomato Spotted Wilt Virus (TSWV) and Late Leafspot (LLS), while MARC I, which is highly susceptible to these diseases, produced very low concentrations of phytoalexins. There was no significant difference in phytoalexin production by undamaged peanut pods of all tested genotypes. Trans-arachidin-3 and trans-resveratrol were the major phytoalexins produced by insect-damaged peanuts. There was an association between total phytoalexin production and published genotypes resistance to TSWV and LLS. Stilbene phytoalexins may be considered potential chemical markers in breeding programs for disease-resistant peanuts, including resistance to preharvest aflatoxin contamination.