Description

Abstract: Conidia of Cercospora arachidicola atombed onto peanut leaves and incubated in dew chambers at 16. 19,22,25.28, or31 C began germinating after 2 hr; maximum germination (82435%) occurred by 24-48 hr at 16-25 C. Germ tube elongation increased linearly up to 48 hr; germ tubes were longest at 22 C and shortest at 16 C. On glass slides coated with a chloroform extract from peanut leaves (coated slides), germination and germ tube elongation were similar to those on leaf surfaces at corresponding temperatures. On coated slides, germination declined rapidly as relative humidity (RH) was reduced from TOO through 98%. although some germination occurred at 94.5% RH after4 days at 24 C. Gcrrn tuber grew to a greater extent at 100% RH than under free water. In wet-dry-wet postinoculation regimes, with the dry period at various humidities, germ tube elongation declined with declining RH. Under condition< favorable. For germ tube growth, 95% of germinated conidia penetrated stomata after 2-32 days and lesions appeared 2-8 days later. After bdays, a mean of four germtubes perconidium was present, althovghan increase in the number of germ tubes did not result in a corresponding increase in the proportion of conidia that penetrated