Assessment of Resistance to Cercospora arachidicola in Peanut Genotypes in Field Plots. H. A. Melouk, USDA, Agricultural Research Service, Stillwater, OK 74076. D. J. Banks, USDA, Agricultural Research Service, Stillwater, OK 74076, and M. A. Fanous, Associate Professor of Statistics, Department of Agricultural Chemistry and Physics, P.O. Box 223, Macdonald Campus of McGill University, Ste. Anne de Bellevue, Quebec, Canada H9X 1C0. Plant Dis. 68:395-397. Accepted for publication 31 October 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/PD-68-395.

Reactions to early leaf spot, caused by Cercospora arachidicola, were evaluated at Perkins, OK, in 1981 on 151 peanut entries representing genotypes of cultivated Arachis hypogaea, wild species of Arachis, and hybrids. Plants were grown in single-row, 3-m plots that were irrigated weekly (2.5–3 cm); leaf spot was evaluated 115–120 days after planting. A subjective scale index of 1–5 (low to high response) was used to describe each of the following criteria: 1) amount of leaf necrosis, 2) degree of sporulation of C. arachidicola, and 3) leaf defoliation. A leaf spot reaction index (LSRI) for each entry was obtained as the product of the leaf necrosis and sporulation indices, where the lowest and highest values of the LSRI were 1 and 25, respectively. The Kruskal-Wallis one-way analysis of variance by ranks and multiple-comparison test were used to test the equality of the effects of genotypes on these criteria. The Spearman rank correlation for each pair of criteria was calculated for each genotype. Significant positive correlations between LSRI and defoliation and between amount of leaf necrosis and defoliation were obtained for all genotypes. Information obtained from this statistical analysis is useful for evaluating resistance of peanut entries to C. arachidicola in field plots on a yearly basis.