EVALUATION OF WHEAT WILD RELATIVES FOR RESISTANCE TO SEPTORIA-TRITICIBLOTCH

Septoria tritici blotch (STB), caused by the fungus Mycosphaerella gra minicola (Fuckel) Schroeter (anamorph: Septoria tritici Roberge in Des maz), is a major disease of wheat (Triticum aestivum L. em. Thell) wor ld wide. The susceptibility of most commercial cultivars to STB has le d to the need to identify new sources of resistance to this disease. A lthough the wild relatives of wheat have provided a valuable source of many new resistance genes, they have not been widely screened for res istance to STB. The objectives of this study were to identify new sour ces of STB resistance from the wild relatives of common wheat and to e xamine relationships among frequency of STB resistant accessions and e cogeographical parameters. Two hundred and fifty-four accessions, with genomes homologous to those of hexaploid wheat, were inoculated in th e greenhouse with a spore suspension of a mixture of 14 S. tritici iso lates collected in Missouri. Accessions with a mean disease reaction < 1 on a 0 to 9 scale, ranging from no visible symptoms (0) to complete necrosis of the inoculated leaf (9), were considered resistant. Pearso n product-moment correlation coefficients were determined for seedling disease susceptibility scores and environmental variables measured at the site of collection of each accession. Eighteen of the 19 resistan t accessions identified were from T. speltoides and T. tauschii. The f requency of resistant accessions was highest in areas of high rainfall and temperature. Targeting areas with these environmental conditions should facilitate future collection of STB resistant germplasm.