Temperature and Relative Humidity Requirements of Species of Penicillium Isolated from Yellow Dent Corn Kernels

SUMMARYTemperature and moisture requirements for germination of conidia and growth on agar were determined for 14 species of Penicillium isolated from corn kernels. Species isolated mainly from unharvested corn grew on agar from 8–35 C, optimally at 30–35 C, and could germinate and sporulate at RH of 86% and above. Species isolated mainly from stored corn grew on agar from –2 to 30–35 C, optimally at 23 C, and could germinate and sporulate at RH of 81–83%. Six species, P. oxalicum and P. funiculosum, the 2 chief field species, P. cyclopium, P. viridicatum and P. brevi-compactum, the 3 chief storage species, and P. expansum were inoculated in equal concentrations into NaClO-treated and untreated lots of 18 and 22% moisture corn (wet wt) and incubated for 13 weeks at 4–35 C. Penicillium funiculosum did not grow. Penicillium oxalicum grew only at 35 C in NaClO-treated 22% moisture corn. In treated and non-treated 22% corn, P. cyclopium and P. viridicatum grew consistently well from 4–30 C. Penicillium expansum initially grew well at these temperatures, but kernel infection decreased with time. Growth of P. brevi-compactum was sparse. At 18%, Penicillia did not grow at 4 C, and only P. brevi-compactum grew well at 16 and 23 C, less well at 30 C. Although not included in the inoculum, P. citrinum infected 100% of the untreated 22% moisture kernels at 35 C in 8 weeks. There appears to be a relationship between the temperature and moisture requirements of species of Penicillium and their occurrence in the field or in storage.