Septoria tritici blotch (STB), caused by Mycosphaerella graminicola (anamorph S. tritici) is currently the most serious foliar disease of wheat worldwide. Understanding of mechanisms for resistance inheritance in genotypes would potentially lead to more efficient deployment of host plant resistance. As part of our effort to improve STB resistance, inheritance of seedling STB resistance was investigated by an eight-parent half diallel set of crosses in Iranian wheat genotypes. Parents and F1 crosses were planted in plastic pot at greenhouse in a randomized complete block design (RCBD) with three replicates. Plants at the second-leaf stage were inoculated with an isolate of S. tritici. Infection response and Picnidia density ratings of the first and second leaves and their AUDPC used for diallel analysis. Significant GCA and SCA were observed in the analysis of variance. The ratio of GCA sum of squares relative to SCA sum of squares suggested that GCA was more important than SCA. Additive alleles effects played the major role in host response to STB in studied varieties. Significant values of both D and H components suggested that all traits were under the control of both additive and dominance gene effects. For all traits high narrow and broad sense heritabilities observed. Recessive genes in infection response, iAUDPC, pAUDPC and dominant alleles in Picnidia density led to decreasing level of traits and increasing resistance to STB. Genotypes Line#10 and N-81-18 had high negative GCA effects and should be promising parents in breeding programs for enhancement of STB resistance.
Key words: Septoria tritici blotch, wheat, diallel, GCA, SCA.
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