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The Distribution and Frequency of Virulence Genes in Geographically Separated Populations of Leptosphaeria nodorum. A. L. Scharen, Agricultural Research Service, U.S. Department of Agriculture, Department of Plant Pathology, Montana State University, Bozeman 59717, USA; Z. Eyal(2), M. D. Huffman(3), and J. M. Prescott(4). (2)Department of Botany, The George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv 69978, Israel; (3)Department of Mathematical Sciences, Montana State University, Bozeman 59717, USA; (4)Wheat Program, The International Maize and Wheat Improvement Center (CIMMYT), El Batan, Mexico. Phytopathology 75:1463-1468. Accepted for publication 8 July 1985. 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, 1985. DOI: 10.1094/Phyto-75-1463.

Virulence frequency of 33 isolates of Leptosphaeria nodorum from eight countries were evaluated on 38 wheat and triticale cultivars. Isolate x cultivar interactions indicate that resistance and virulence have some specific effects. A computer program that estimates the number of genes, assuming a gene-for-gene relationship, was used to analyze the interacting matrix. The analysis hypothesized 21 different interacting genes in the 33-isolate x 38-cultivar matrix. The winter bread wheat, Red Chief, was assigned 19 hypothetical genes for resistance; cultivars Yamhill, 81UWWMN 2095, and MT 71-8-10 also were assigned large numbers of hypothetical genes. Isolates of L. nodorum from South America (Brazil, Chile, and Ecuador) expressed high relative virulence with those from Canadian and United States populations following. Among the United States isolates of L. nodorum, those from Louisiana and Florida exhibited the highest relative virulence. Some wheat and triticale accessions exhibited a low percent necrosis in response to populations of both L. nodorum and Mycosphaerella graminicola that have wide virulence spectra. The cultivars most resistant to populations of the two pathogens were the winter hexaploid wheat cultivars JCR-979 (CI 16906), Red Chief (CI 12109), 81UWWMN 2095 (Maris Huntsman//VPM/Moisson), and triticale accession DU-75. A Bobwhite S CIMMYT line expressed the highest level of resistance to both pathogens among the spring hexaploid wheats. The implications of these findings on the deployment of germplasm and the accumulation of resistance to both pathogens is discussed.

Additional keywords: glume blotch, Septoria nodorum, Septoria tritici, speckled leaf blotch.