Genetic adaptability of the inheritance of the resistance to different levels of aggressiveness of Septoria tritici isolates in durum wheat

The aim of this study was to evaluate the variation in the mode of inheritance for resistance in durum wheat to Septoria tritici with the aggressiveness level of the pathogen. Material for the study involved two wheat cross-combinations and offspring populations. In each cross, the parental genotypes, F1, F2, BC1Pr and BC1Ps were inoculated with 15 isolates of S. tritici with different levels of aggressiveness. Generation mean analysis revealed that the mode of inheritance varied with the aggressiveness level of isolates. For less aggressive isolates, in both crosses, only additive and dominance effects were determined. When tested with isolates with moderate levels of aggressiveness, the additive-dominance model was not sufficient to explain the variation in generation means; and a di-genic epistasis model was found appropriate. For a high level of aggressiveness, both additive-dominance and di-genic epistatic models failed to explain the phenotypic variation in generation means, and probably higher order interaction or genes linkage were present. The quantification of gene effects revealed that the absolute total of epistatic effects increased with aggressiveness level of the isolate. Selection based on less aggressive isolates would be simpler, because only additive and dominance effects are implicated, but the genetic mechanism will not be stable with isolates of high aggressiveness level. Thus, selection with highly aggressive isolats is suggested for the stability of resistance to S. tritici in durum wheat.

► Inheritance varied with the aggressiveness level of isolates.
► Absolute total of epistatic effects increased with aggressiveness level of the isolate.
► Selection with highly aggressive isolates is suggested for the stability of resistance.