Evaluation of Peanut (Arachis hypogaea L.) Germplasm for Resistance to Aflatoxin Production by Aspergillus flavus Link ex Fries

Abstract

Aflatoxins are carcinogenic and toxic secondary metabolites produced primarily by the fungi Aspergillus flavus Link ex Fries and A. parasiticus Speare. Aflatoxin contamination of peanut is a serious worldwide problem. Aflatoxin resistant cultivars should be a component of an integrated program of aflatoxin management. Peanut genotypes with resistance to in vitro seed colonization (IVSCAF), field seed colonization (FSCAF) and preharvest aflatoxin contamination (PAC) have been reported, but no germplasm highly resistant to aflatoxin production has been found in cultivated peanut. A technique was developed to identify genotypes with resistance to aflatoxin production when subjected to post-harvest conditions conducive to fungal growth and aflatoxin synthesis. This technique provides environmental control and generally results in a low coefficient of variation in the data. Using this technique, the effect of the high-oleate trait on aflatoxin production was tested by comparing normal oleic lines with high-oleic backcross-derived lines. High-oleate peanuts supported more aflatoxin than normaloleate lines, but the magnitude of the difference varied with background genotype. To determine if linoleate concentration in seed oil could be used to predict levels of aflatoxin production, seeds of genotypes representing a range of linoleate concentration were tested. Low-linoleate lines consistently contained more aflatoxin, while normal- to highlinoleate lines contained variable amounts of aflatoxin. Although fatty acid profiles accounted for significant portions of the genetic variation, fatty acid concentration was not a reliable predictor of aflatoxin production, especially for lines in the normal range for oleate and linoleate. The same technique was used to evaluate seven accessions of A. cardenasii Krapov. and W.C. Gregory, 29 accessions of A. duranensis Krapov. and W.C. Gregory, and 17 interspecific tetraploid lines derived from A. cardenasii. The two diploid wild species averaged significantly less aflatoxin contamination than A. hypogaea checks, but were not different from each other. Arachis duranensis accessions PI 468319, PI 468200, and PI 262133, and A. cardenasii accessions PI 262141 and PI 475997 had very low levels of aflatoxin contamination and should be valuable sources of resistance to aflatoxin contamination. Of the interspecific tetraploid lines, only GP-NC WS 2 supported aflatoxin production not significantly different from resistant parent A. cardenasii GKP 10017. It appears to be a line with reduced capacity for aflatoxin accumulation. To identify germplasm with more than one type of resistance, lines previously reported with resistance to IVSCAF, FSCAF or PAC were tested. The results suggested that there were no strong correlations of IVSCAF, FSCAF or PAC resistance with aflatoxin production resistance, so it should be possible to combine high resistance to IVSCAF, FSCAF, or PAC with aflatoxin production in a single genotype. PI 590325, PI 590299, PI 290626, and PI 337409 accumulated the lowest amounts of aflatoxin among all A. hypogaea lines tested. These genotypes and susceptible check Perry were used to test interactions between peanut genotype and strain of Aspergillus species. Aspergillus species and strain had more effect on aflatoxin production than did peanut genotype. There were significant interactions between peanut genotypes and strains within species. These results suggest that the technique might be improved by using a mixture of several aflatoxigenic strains of A. flavus and A. parasiticus to identify genotypes with stable and low aflatoxin contamination. A population developed by crossing resistant genotype PI 290626 with susceptible cultivar Gregory was used to study inheritance of resistance to aflatoxin production. The primary form of genetic variance in this population was nonadditive, suggesting that selection within the population will be ineffective in early segregating generations.