ANALYSIS OF THE GENETIC-RELATIONSHIPS AMONG THE WHEAT BUNT FUNGI USING RAPD AND RIBOSOMAL DNA MARKERS

Ninety-five isolates of Tilletia controversa, T. tritici, T. laevis, a nd T. fusca var. bromi-tectorum were assayed for random amplified poly morphic 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, w hich 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 iso lates of T. controversa and RG IB containing 38 isolates of T. tritici , T. laevis, and six isolates of T. controversa. Bootstrap analysis su pported the separation between isolates from wheat and isolates from c heatgrass, but not the clustering of isolates within the wheat bunt gr oup. However, the g1 statistic, a measure of the skewness of the tree- length distribution, indicated a significant difference between the dw arf bunt and common bunt clusters (P < 0.05). Restriction digestion an alysis of the 5.8s and internal transcribed spacer region of ribosomal DNA in a subset of wheat bunt fungi (28 isolates of T. controversa, 1 9 isolates of T. tritici, and 12 isolates of T. laevis) showed two dis tinct patterns. Haplotype A was associated with 24 of 28 isolates of T . controversa and haplotype B was associated with all isolates of comm on 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 b oth dwarf and common bunt fungi raises the question of whether natural hybridization is responsible for the apparent recombination of charac ters.