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Influence of Temperature and Moisture on Germination and Germ Tube Elongation of Cercospora arachidicola. S. C. Alderman, Research associate, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; M. K. Beute, professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 76:715-719. Accepted for publication 27 January 1986. Copyright 1986 The American Phytopathological Society. DOI: 10.1094/Phyto-76-715.

Conidia of Cercospora arachidicola atomized onto peanut leaves and incubated in dew chambers at 16, 19, 22, 25, 28, or 31 C began germinating after 2 hr; maximum germination (82-85%) 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 100 through 98%, although some germination occurred at 94.5% RH after 4 days at 24 C. Germ tubes 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 conditions favorable for germ tube growth, 95% of germinated conidia penetrated stomata after 2-12 days and lesions appeared 2-8 days later. After 6 days, a mean of four germ tubes per conidium was present, although an increase in the number of germ tubes did not result in a corresponding increase in the proportion of conidia that penetrated.

Additional keywords: Arachis hypogaea, early leaf spot.