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Effects of Temperature and Relative Humidity on Expression of Resistance to Cercosporidium personatum in Peanut. B. B. Shew, Research associate, Department of Crop Science, North Carolina State University, Raleigh 27695-7616; M. K. Beute(2), and J. C. Wynne(3). (2)Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616; (3)Professor, Department of Crop Science, North Carolina State University, Raleigh 27695-7616. Phytopathology 78:493-498. Accepted for publication 21 October 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-493.

Detached peanut leaves were inoculated with the leaf spot pathogen Cercosporidium personatum and exposed to 20, 24, 28, or 32 C for 6 days. Maximum infection occurred at 20 C, provided leaves also were exposed to at least 12 hr/day high relative humidity (RH > 93%). Infection of genotypes with high (PI 259747, NC Ac 17133), moderate (GP-NC 343), and low (NC 3033, Robut 33-1) partial resistance decreased with increasing temperature. Few infections occurred at 28 and 32 C regardless of duration of the high relative humidity period. Daily periods of high relative humidity shorter than 12 hr also reduced the number of infections on all genotypes regardless of temperature. Ranking of genotypes by lesion numbers was similar at all temperature and relative humidity periods tested. Lesions on leaves of PI 259747, NC Ac 17133, GP-NC 343, NC 3033, and Robut 33-1 were largest, developed most rapidly, and sporulated most profusely at 24 C. Lesions on FESR 5-P2-B1, a genotype reported to have high combining ability for leaf spot resistance, developed fastest at 28 C. Postinfection development of C. personatum was completely inhibited at 28 C on the highly resistant genotypes, and at 32 C on all genotypes.

Additional keywords: Arachis hypogaea, groundnut.