Suraj Gurung, Department of Plant Pathology, University of California, Davis, c/o U.S. Agricultural Research Station, Salinas, CA 93905;
Baidya N. Mahto, Division of Plant Pathology, Nepal Agricultural Research Council, Khumaltar, Lalitpur, Nepal;
Sanjaya Gyawali, Agriculture and Agri-Food Canada, Saskatoon Research Centre, 107 Science Place, Saskatoon, Saskatchewan, S7N 0X2, Canada; and
Tika B. Adhikari, Center for Integrated Pest Management and Department of Plant Pathology, North Carolina State University, 840 Main Campus Drive, Partners II Suite 1400, Centennial Campus, Raleigh 27606
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Accepted for publication 22 July 2012.
Spot blotch, caused by Cochliobolus sativus, is a devastating foliar disease of wheat in Nepal and in the Northern Great Plains of the United States. However, limited information on variation in virulence and genetic structure of C. sativus from wheat is available. In this study, pathogenic variation of 96 isolates of C. sativus from the Hill and Plain areas in Nepal (n = 48) and in the Central and Northern areas in North Dakota (n = 48) were evaluated on 12 differential wheat lines. DNA polymorphisms in all isolates were analyzed using eight selected amplified fragment length polymorphism primer combinations. Phenotypic data analysis showed the isolates varied greatly and were classified into 47 pathotypes. Cluster analysis indicated the isolates fell into three distinct groups with low, intermediate, and high virulence. Population genetic analysis revealed significant linkage disequilibrium (rd = 0.066 to 0.292), indicating that sexual reproduction plays little or no role in evolution and disease epidemiology in wheat fields. Furthermore, the corrected standardized fixation index (G″ST = 0.05 and 0.02) showed no evidence of genetic differentiation in C. sativus populations. Collectively, these results confirmed high pathogenic and molecular diversity in the C. sativus populations collected from wheat foliar infections and will be useful to assist in developing resistant cultivars to manage this disease.
© 2013 The American Phytopathological Society