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Genetic Analysis of Two Race 0 ◊ Race 2 Crosses in Cochliobolus carbonum. H. G. Welz, Wissenschaftlicher Mitarbeiter, Institute of Plant Breeding, Seed Science, and Population Genetics, University of Hohenheim (762), 70593 Stuttgart, Germany; formerly postdoctoral research associate, Tropeninstitut der Justus-Liebig-Universitšt, 35390 Giessen, Germany; K. J. Leonard, research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Cereal Rust Laboratory, University of Minnesota, St. Paul 55108; formerly research plant pathologist, U.S. Department of Agriculture, Agricultural Research Service, Department of Plant Pathology, Box 7616, North Carolina State University, Raleigh 27695-7616. Phytopathology 84:83-91. Accepted for publication 26 August 1993. 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, 1994. DOI: 10.1094/Phyto-84-83.

Progeny from two crosses of race 0 ◊ race 2 of Cochliobolus carbonum segregated in 1:1 ratios for loci controlling mating type, fungicide tolerance, and ability to sporulate on potato-dextrose agar. Segregations at single loci also were observed for three isozyme systems and for one of two bands in a fourth system. Progeny also segregated for four esterase bands, but the segregation patterns were complex. Pathogenicity to corn was inherited as two apparently complementary genes present in race 2 but lacking in race 0, which was avirulent on corn. Evidence was found for a new locus for production of pseudothecia and a new locus for production of asci and ascospores. These putative loci differ from the previously described single loci for pseudothecium and ascospore production in C. carbonum. Gene mapping analysis identified two linkage groups: one 11 cM (centiMorgans) long with two linked loci for esterase bands, and one 164 cM long with six loci including the mating type locus, one locus for cadmium tolerance, and two loci for esterase bands. A quantitative trait locus for conidium production was found within 2 cM of the Est-B92 locus of the larger linkage group. The frequency distributions among race 0 ◊ race 2 progeny for the numbers of conidia and pseudothecia produced were skewed toward poor production by most of the progeny relative to the parents.

Additional keywords: Bipolaris zeicola, Helminthosporium carbonum, linkage analysis, maize, QTL mapping, Zea mays.