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Postharvest Pathology and Mycotoxins

The Effects of Heat Treatment and Inoculum Concentration on Growth and Sporulation of Penicillium spp. on Corn Genotypes in Storage. Bamo Yao, Graduate student, Department of Botany and Plant Pathology, Purdue University, W. Lafayette, IN 47907; John Tuite, professor, Department of Botany and Plant Pathology, Purdue University, W. Lafayette, IN 47907. Phytopathology 79:1101-1104. Accepted for publication 8 June 1989. Copyright 1989 The American Phytopathological Society. DOI: 10.1094/Phyto-79-1101.

The effects of heat treatment and inoculum concentration of Penicillium brevi-compactum, P. cyclopium, and P. viridicatum on storability of corn kernels were determined in separate tests for 10 genotypes of dent corn and a visual flint (VF) selection. Hand-shelled corn grown during 1983–1985 was used. Kernels of B73 × Mo17 and Dekalb XL67, resistant, and H95 very susceptible and VF, moderately susceptible to storage Penicillia were heated at 80 C for 20 min, then inoculated with 2 × 10³ spores/g and stored at 88% RH and 14 C for 49 days. Host reaction was determined by a visible mold rating on individual kernels and number of propagules isolated after dilution on a modified potato-dextrose agar. Molding was substantially increased by the heat treatment as measured by propagules and less so by visible mold for all four genotypes. Increase was greater for the resistant hybrids but the disease rankings among the genotypes remained. The heat-treated resistant hybrids did not support significantly more sporulation of Penicillium than the unheated, susceptible genotypes. In three tests, a total of 11 corn genotypes were inoculated with 2 × 10³ to 10⁴ or 2 × 10³ to 10⁵ spores of Penicillium spp. per gram of corn and stored at 13–14 C and 88% RH. Increasing the inoculum to either 10⁴ or 10⁵ spores/g generally had no significant effect on relative resistance as measured by propagules and visible mold, although there was an increase in propagules with an increase in the amount of inoculum, particularly when 2 × 10⁴ or 10⁵ spores/g was used. There appeared to be a more defined separation of hybrids with inoculum at 2 × 10⁴ and 10⁵ than at 2 × 10³ spores/g.