Recent Occurrence of Puccinia graminis f. sp. tritici in Italy: Pathogen Virulence Composition and Seedling Resistance of Durum and Common Wheat

Regular disease monitoring is currently carried out in the most important Italian wheat growing areas. In 2007-08 stem rust was absent in all locations tested except Montelibretti (Rome, Central Italy), where two common wheat varieties "Arsenal" and "Compair" had stem rust infections. Two stem rust pathotypes were identified by testing in the greenhouse a set of differential lines/varieties carrying known genes for resistance to Puccinia graminis. These pathotypes corresponded to races MSK and PTK on the basis of the North American classification system. Genes Sr24 and Sr25 (both derived from Thinopyrum ponticum) and Sr31 (from Secale cereale), were resistant to the Italian pathotypes, and the lines carrying Sr38 (from Triticum ventricosum) were susceptible. Tests were carried out to determine the seedling stem rust response of durum and common wheat cultivars grown in Italy. Many durum wheat genotypes were resistant to MSK and PTK, while several common wheats were susceptible. The different response of the two species could be due to the source (common wheat) of stem rust inoculum. Molecular PCR markers, linked to Sr24, Sr25, Sr31 and Sr38, were used to detect their presence/absence in the genetic background of the durum and common wheat cultivars. The presence of Sr31 was shown in only two common wheat cultivars ("Colledoro" and "Sollario"), while several genotypes carried Sr38. No common wheat genotype was positive (to PCR analysis) for the presence of Sr24 or Sr25 genes, whereas no durum wheat was positive for the presence of Sr24, Sr25, Sr31 or Sr38.