Screening peanut genotypes (Arachis hypogaea L.) for resistance to Aspergillus flavus, A. parasiticus and aflatoxin contamination

Abstract

Twenty-three peanut genotypes (Arachis hypogaea L.) were evaluated for kernel resistance to Aspergillus parasiticus infection under high relative humidity. The lowest degree of infection, less than 30% was noted in kernels from the genotypes Toalson x UF73-4022 (85WAPAF4), A72118, SN 55-437, Toalson x UF73-4022 (84B4308), PI 337409 and Florunner. Peanut genotypes were tested in greenhouse and microplot experiments in two years to determine their susceptibility to A. flavus infection under stress treatments. Isolation frequencies from pegs both years in the greenhouse experiments were highest in pegs from the cultivar J-11 and lowest in pegs from the genotype PI 337409. The extent of shell and kernel infestation from plant parts from each of the three stress treatments in both years revealed that shells and kernels of all 3 cultivars tested were highly infested following drought stress treatments imposed 100 days after planting until harvest (WS). The microplot experiments conducted in 1985 and 1986 revealed that aerial peg infestation both years was different. Tannin extracts from peanut pegs (25 mg/l of YES liquid medium) did not significantly influence mycelial growth of A. parasiticus or aflatoxin production in the 1985 experiment. Results from the microplot experiment conducted in 1985 revealed that the highest recovery of A. flavus was detected in the kernels from the WS treatment, with exception of the genotypes SN 55-437 and PI 337409. Several phenolic compounds were tested for their ability to inhibit A. parasiticus growth and aflatoxin production. Growth inhibition for these compounds at concentrations of 100 and 1000 mg/l YES medium was greatest using tannic acid, catechol and methyl catechol. Aflatoxin production was significantly inhibited by methyl catechol, naringenine, and umbelliferone. Tannin-related compounds were extracted from the seed coats and cotyledons of twenty-three peanut genotypes. Higher levels of tannins (86.2-97.2 mg/g tissue) were extracted from the seed coats compared to the cotyledons (0.17-0.82 mg/g tissue). Some of the tannin extracts from seed coats and cotyledons (100 mg/l YES liquid medium) significantly inhibited fungal growth and partially reduced the levels of aflatoxins produced.