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Resistance

Susceptibility of Pods of Different Peanut Genotypes to Aspergillus flavus Group Fungi. A. C. Kushalappa, Former research assistant, University of Florida, Gainesville 32611, Present address: Professor titular, Departmento de Fitopatologia, Universidade Federal de Viçosa, 36.570-Viçosa-MG-Brazil; Jerry A. Bartz(2), and A. J. Norden(3). (2)(3)Associate professor of plant pathology, and professor of agronomy, respectively, University of Florida, Gainesville 32611. Phytopathology 69:159-162. Accepted for publication 31 August 1978. Copyright 1979 The American Phytopathological Society. DOI: 10.1094/Phyto-69-159.

Pods and seeds from 17 peanut genotypes were tested for resistance to colonization by Aspergillus parasiticus after each of two successive growing seasons. In each year’s tests, pods of three genotypes remained completely free from colonies of the test fungus, whereas all the pods of two genotypes in the first year and of three genotypes in the second year had at least one colony. The percentage of inoculated pods with surface colonies of A. parasiticus was not directly proportional to that of inoculated seeds; rather, they were inversely correlated (r = –0.5 and –0.6 in tests 1 and 2, respectively). Thus, peanuts selected for resistance to A. parasiticus through the standard inoculated seed assay would usually produce pods that are more susceptible to colonization than would genotypes producing more susceptible seed. The shell of the intact pod seemed to provide an effective barrier to A. parasiticus. The quantity of aflatoxin B₁ in seeds of four genotypes was correlated (r = 0.89) with the percentage of pods with surface colonies at 21 days after inoculation. The latter values also were correlated (r = 0.89 and 0.94) with the percentage of seeds that had been penetrated and those with surface colonies, respectively. Resistance of pods to A. parasiticus, however, may not be a true plant resistance, since genotypes that were relatively resistant one year were susceptible the next, and vice versa. Colonies arising from natural inoculations occurring before the pods were artificially inoculated accounted for only three of the seven significant changes in the percentage of pods with colonies between the first and second tests.