Seed and Plant Improvement Institute, Karaj, Iran.
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 128 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 20-22ºC and scored 21 days post inoculation by estimating the percentage of necrotic lesions bearing pycnidia. Inter simple sequence repeat (ISSR) markers revealed that 11 Z. tritici isolates had high genetic variability. The isolates varied in their virulence towards SHWs. Among all interactions (n=1408), 304 resistance responses were identified. Of 128 genotypes, 60 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 RM46 collected from Khuzestan Province was virulent on 87% of SHWs, suggesting that it has the lowest number of avirulence genes. Isolate RM155 collected from Golestan Province displayed the highest number of incompatible interactions (n=42), indicating that it possesses the highest number of avirulence genes. RM151 was the most aggressive isolate with the highest mean disease severity (69%), whereas RM41 was the least aggressive isolate with the lowest mean disease severity (37%). 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.