Genetic analysis of resistant to Septoria tritici Blotch using Diallel crosses

Background and objectives: Septoria tritici blotch (STB), caused by Mycosphaerella graminicola (anamorph S. tritici) is currently the most serious disease of wheat worldwide. This study was established to determine the function of resistant genes of M. graminicola to find out the number of genes corresponding in resistant reaction and also to estimate the genetic parameters of resistance.
Materials and methods: Eight winter wheat genotypes were selected based on preliminary field and greenhouse observations of their reaction to S.tritici. Twenty-eight F1 wheat genotypes derived from an eight-parent half diallel set of crosses and their parents were planted in a randomized complete block design (RCBD) with three replications. Plants were inoculated in tillering, long stem and appearance of flag leaf stages. Disease rating was visually recorded by using the double-digit scale (00–99). Data analysis by Hyman & Jinks method was performed using D2 genetic software. Disease severity and it's AUDPC (sAUDPC) were calculated.
Results: For the validity of additive-dominance model, two scaling tests were employed following Mather and Jinks . For both traits, the regression coefficient test, indicated that b differed significantly from zero but not from unity and according to second test, t2 was not significant, Thus, both tests suggested adequacy of the additive-dominance model for these characters. Following Mather and Jinks for both traits, the regression coefficient test indicated that b differed significantly from zero but not from unity and also t2 value was not significant that validate additive-dominance model. The ratio of dominance effect of heterozygous loci to corrected dominance variance for both traits was less than 1 suggesting the control of one gene group. High narrow and broad sense heritabilities were recorded for both traits (over 80% and 95% respectively) . Greater portion of heritable variation was of additive nature. Line10 caries additive resistant genes, so selection would be effective. Dominant alleles in d,isease severity and sAUDPC led to decreasing level of traits and increasing resistance to Septoria Tritici Blotch. Since the selection of resistant generations of crosses between parents based on their cross direction is predictable, by crossing parents with high resistance can improve wheat genotypes Septoria Tritici Blotch resistance. Based on the results doing cross between line#10 and N-81-18 to produce suitable cultivar with permanent resistance to Septoria Tritici Blotch is recommended.
Conclusion: Results showed additive effects are responsible for much of the variance of heritability. Genotype line#10 had most of the resistance genes to Septoria Tritici Blotch compared to other genotypes which suggested as donor parent for resistance genes in breeding programs.