Race-specific resistance of wheat to Puccinia graminis f. sp. tritici is primarily posthaustorial and often involves the induction of a hypersensitive response (HR). The aim of this study was to investigate host defense responses induced in interactions between P. graminis f. sp. tritici races and wheat lines carrying different race-specific stem rust resistance (Sr) genes. In incompatible interactions between wheat lines carrying Sr36 in three genetic backgrounds (LMPG, Prelude, or W2691) and avirulent P. graminis f. sp. tritici races MCCFC or RCCDM, callose accumulated within 24 h in wheat guard cells contacted by a P. graminis f. sp. tritici appressorium, and P. graminis f. sp. tritici ingress was inhibited following appressorium formation. Accordingly, the expression of transcripts encoding a callose synthase increased in the incompatible interaction between LMPG-Sr36 and avirulent P. graminis f. sp. tritici race MCCFC. Furthermore, the inhibition of callose synthesis through the infiltration of 2-deoxy-D-glucose (DDG) increased the ability of P. graminis f. sp. tritici race MCCFC to infect LMPG-Sr36. A similar induction of callose deposition in wheat guard cells was also observed within 24 h after inoculation (hai) with avirulent P. graminis f. sp. tritici race HKCJC on LMPG-Sr5 plants. In contrast, this defense response was not induced in incompatible interactions involving Sr6, Sr24, or Sr30. Instead, the induction of an HR and cellular lignification were noted. The manifestation of the HR and cellular lignification was induced earlier (24 hai) and was more extensive in the resistance response mediated by Sr6 compared with those mediated by Sr24 or Sr30. These results indicate that the resistance mediated by Sr36 is similar to that mediated by Sr5 but different from those triggered by Sr6, Sr24, or Sr30. Resistance responses mediated by Sr5 and Sr36 are prehaustorial, and are a result of very rapid recognition of molecules derived from avirulent isolates of P. graminis f. sp. tritici, in contrast to the responses triggered in lines with Sr6, Sr24, and Sr30.

Wheat leaf rust caused by Puccinia triticina (Pt) is one of most severe fungal diseases threatening global wheat production. Rational utilization of the diversified leaf rust resistance (Lr) in different wheat cultivars is still the most efficient method to control this disease. Here in this study, 35 wheat cultivars collected from China main wheat growth region were tested for their seedling resistance to 16 different Pt races. Seedlings of 20 tested wheat cultivars showed high resistance phenotype to at least one Pt race. Various molecular markers closely linked to fifteen designated Lr genes were applied and only three Lr genes (Lr1, Lr10 and Lr26) were identified in some of the tested cultivars. All cultivars were then inoculated with bulked Pt races mixed with even of 10 pathotypes at adult plant stage to detect the adult plant resistance (APR). Five cultivars including Liangxing 66, Hemai 9735, Luyuan 301, Jimai 17 and Taishan 027 showed typical APR reaction in the field. Our results indicate that the diversity of known Lr genes in the tested wheat cultivars is relative low, but 10 of them contained more durable leaf rust resistance and can be released in wheat production and can be used as resistance breeding resources.