Evaluation of CIMMYT synthetic hexaploid wheats for resistance to septoria tritici blotch

Synthetic hexaploid wheats (SHWs) are an important component of the breeding programs of the International Maize and Wheat Improvement Center (CIMMYT). CIMMYT germplasm is the most important source of genetic resources for wheat breeding programs in Iran, but their utilization has to be examined prior to their incorporation into breeding programs. This study was conducted to evaluate the resistance of ۱۲۸ CIMMYT SHWs to septoria tritici blotch (STB), a destructive wheat disease caused by Zymoseptoria tritici. Wheat seedlings were inoculated with Z. tritici spores in the greenhouse, kept at ۲۰-۲۲ºC and scored ۲۱ days post inoculation by estimating the percentage of necrotic lesions bearing pycnidia. Inter simple sequence repeat (ISSR) markers revealed that ۱۱ Z. tritici isolates had high genetic variability. The isolates varied in their virulence towards SHWs. Among all interactions (n=۱۴۰۸), ۳۰۴ resistance responses were identified. Of ۱۲۸ genotypes, ۶۰ synthetic hexaploid wheat genotypes showed no resistance response, whereas the remaining genotypes showed specific resistance to one or more isolates. Interestingly, nine genotypes were resistant to all isolates tested. Isolate RM۴۶ collected from Khuzestan Province was virulent on ۸۷% of SHWs, suggesting that it has the lowest number of avirulence genes. Isolate RM۱۵۵ collected from Golestan Province displayed the highest number of incompatible interactions (n=۴۲), indicating that it possesses the highest number of avirulence genes. RM۱۵۱ was the most aggressive isolate with the highest mean disease severity (۶۹%), whereas RM۴۱ was the least aggressive isolate with the lowest mean disease severity (۳۷%). The present study was the first conducted to evaluate CIMMYT SHWs for resistance to Iranian Z. tritici isolates. Our results showed that some SHWs possess a broad spectrum of resistance gene(s) or a combination of a set of effective genes against various STB isolates.