Peanuts become contaminated with aflatoxins when subjected to prolonged periods of heat and drought stress. The effect of drought tolerance on aflatoxin contamination is not known. The objectives of this research were to evaluate preharvest aflatoxin contamination in peanut genotypes known to have drought tolerance and to determine the correlation of drought tolerance characteristics with aflatoxin contamination. Twenty genotypes with different levels of drought tolerance were grown in Yuma, AZ (a desert environment) and under rain-protected shelters in Tifton, GA. Two drought-tolerant genotypes (PI 145681 and Tifton 8) and an intolerant genotype (PI 196754) were selected for further examination in a second experiment with two planting dates in 1997 at Tifton. Drought and heat stress conditions were imposed for the 40 d preceding harvest. The drought-intolerant genotype had greater preharvest aflatoxin contamination than Florunner (the check cultivar) in the tests conducted in 1997. Both drought-tolerant genotypes had less preharvest aflatoxin contamination than Florunner in these tests. Significant positive correlations were observed between aflatoxin contamination and leaf temperature and between aflatoxin contamination and visual stress ratings. Leaf temperature and visual stress ratings are less variable and less expensive to measure than aflatoxin contamination. Leaf temperature and visual stress ratings maybe useful in indirectly selecting for reduced aflatoxin contamination in breeding populations.
Peanut ( Arachis hypogaea L.) is susceptible to aflatoxin contamination when pods are developing under drought conditions in the field. The development of cultivars which resist preharvest aflatoxin contamination would be advantageous, but has been limited by the lack of genes for resistance. Several genotypes have been suggested as potential sources of resistance. Conflicting results have been reported on how useful this resistance may be, and some of these sources have never been specifically examined for resistance to preharvest aflatoxin contamination. The objective of this study was to evaluate aflatoxin contamination under drought stressed conditions in potentially resistant peanut genotypes. Twelve peanut genotypes were planted in a randomized complete-block design in field plots in Yuma, AZ in 1991 and 1992. Ten of these genotypes were also planted in a randomized complete-block design in field plots in Tifton, GA in 1992. All plots were inoculated with Aspergillus inoculum and were subjected to 40 to 50 d of drought stress immediately prior to harvest. After harvest, aflatoxin contamination (ppb) of seed was measured. None of the genotypes included in this study were more resistant (P≤0.05) to preharvest aflatoxin contamination than Florunner. The results of this study indicate that it would be desirable to identify higher levels of resistance to preharvest aflatoxin contamination in peanut.