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Analysis of the Genetic Relationships Among the Wheat Bunt Fungi Using RAPD and Ribosomal DNA Markers. Y. L. Shi, Department of Plant Pathology, Washington State University, Pullman 99164-6430; P. Loomis, D. Christian, L. M. Carris, and H. Leung. Department of Plant Pathology, Washington State University, Pullman 99164-6430. Phytopathology 86:311-318. Accepted for publication 30 November 1995. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-311.

Ninety-five isolates of Tilletia controversa, T. tritici, T. laevis, and T. fusca var. bromi-tectorum were assayed for random amplified polymorphic DNA (RAPD). Based on 23 RAPD markers, two distinct RAPD groups (RG I and RG II) with 12% similarity were obtained using the distance matrix method. RG I included all 66 isolates of the wheat bunt fungi and RG II contained all 29 isolates of T. fusca var. bromi-tectorum, which was considered as an outgroup. RG I was further divided into two subgroups RG IA and RG IB with 75% similarity: RG IA containing 19 isolates of T. controversa and RG IB containing 38 isolates of T. tritici, T. laevis, and six isolates of T. controversa. Bootstrap analysis supported the separation between isolates from wheat and isolates from cheatgrass, but not the clustering of isolates within the wheat bunt group. However, the g1 statistic, a measure of the skewness of the tree-length distribution, indicated a significant difference between the dwarf bunt and common bunt clusters (P < 0.05). Restriction digestion analysis of the 5.8s and internal transcribed spacer region of ribosomal DNA in a subset of wheat bunt fungi (28 isolates of T. controversa, 19 isolates of T. tritici, and 12 isolates of T. laevis) showed two distinct patterns. Haplotype A was associated with 24 of 28 isolates of T. controversa and haplotype B was associated with all isolates of common bunt fungi and four isolates of T. controversa. The data suggested that the wheat bunt fungi descended from a common ancestral population that subsequently differentiated into two sublineages. The fact that a considerable number of isolates have reciprocal characteristics of both dwarf and common bunt fungi raises the question of whether natural hybridization is responsible for the apparent recombination of characters.

Additional keywords: phylogenetic lineage.