Abstract

Several studies that attempt to identify the genetic basis of quantitative traits ignore the presence of epistatic effects and theirs role in plant genetic adaptability. Epistasis has been detected in the inheritance of many quantitative traits on crop. Moreover, generation means analysis of several traits assessed in diverse environmental conditions revealed that the mode of inheritance of each trait varied with the biotic or abiotic stress level. With less stress level, only additive and dominance effects was found significant. In contrast with moderate and higher stress level, epistatic effect was induced. Thus, a relationship was found between the complexity of model of inheritance and stress level. When the biotic or abiotic stress increases, epistasis effect was solicited and the more the stress increase, the amplitude of epistasis was more important and the model of inheritance was more complicated. This result was showed for resistance to 15 isolates of Septoria tritici in durum wheat with different levels of aggressiveness; for resistance to six isolates of Phytophthora nicotianae in pepper and for resistance to five salt concentrations at germination stage in durum wheat. Indeed, the generic effects of environment on genetic model of inheritance complicate the procedure of amelioration of quantitative traits. Hence, it is becoming evident that plant genetically expressed differences when operated in wide range of environments, and epistasis play a crucial role in genetic adeptness. The best way of crop breeding must therefore be investigated in each special environment.

Key words: Epistasis, quantitative traits, genetic adaptation, environment.