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Genes for Pathogenicity in Cochliobolus carbonum. R. R. Nelson, Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 60:1335-1337. Accepted for publication 2 April 1970. DOI: 10.1094/Phyto-60-1335.

The pathogenicity of 485 ascospore isolates from six different crosses of Cochliobolus carbonum (Helminthosporium carbonum) isolates to seven differential gramineous species was determined. A min of nine previously unreported genes for pathogenicity to seven grass species was identified. Segregation ratios and comparisons of reactions of paired differential hosts demonstrated that pathogenicity to five of the seven gramineous hosts is controlled by five different genes. Pathogenicity to two species is conditioned by two different sets of two genes each. Analyses of frequencies of parental and recombinant progeny indicated that seven of the nine identified genes for pathogenicity are independently inherited. Linkage was detected between the remaining two genes. Linkage was detected also between the gene for pathogenicity to Cynodon dactylon and the mating type locus in one cross. Additional segregation data identified linkage relationships between genes for pathogenicity reported herein and those reported previously.