Variation of gene effects of six agronomic traits with water regimes in durum wheat

This study was carried out to determine the relative importance of additive, dominance and epistatic effects of six agronomic traits evaluated in two crosses under irrigated and rainfed conditions. Separate generations mean analyses revealed that gene effects were dependent upon water regime. Under irrigated regime, only additive and dominance effects were implicated in inheritance of all traits, except plant height in the two crosses and grains per spike in the cross Razzek × Chili. However, under rainfed condition, additive, dominance and epistasis effects were induced in the genetic control of these traits. Thus, epistasis effect was water regime depended and seems to play a significant role in the genetic adaptability of populations. The variation of inheritance and the presence of genetic interactions complicate the procedure of breeding. Under irrigated regime, selection would be simpler because only additive and dominance effects were implicated in the genetic control of all traits. Consequently, the genetic mechanism would not be stable when plants are grown in environment with lower water availability. However, for the stability of suitable cultivars, selection under rainfed condition (lower water availability) was suggested. The moderate to high narrow-sense heritability estimates for the majority of traits indicate that selection would be efficient.Keywords: Durum wheat, epistatic effect, genetic adaptability, heritability, water regimeAfrican Journal of Biotechnology Vol. 12(15), pp. 1769-177

Relationship between epistasis and aggressiveness in resistance of pepper (Capsicum annuum L.) to Phytophthora nicotianae

This study evaluated the types of gene action governing the inheritance of resistance to Phytophthora nicotianae necrosis in populations derived from two crosses involving two susceptible (Beldi and Nabeul II) and one resistant (CM334) cultivars of pepper (Capsicum annuum L.). Populations, composed of Pr, Ps, F1 , F 2 , BC 1 Pr, and BC 1 Ps generations, were inoculated with six P. nicotianae isolates. Generation means analysis indicated that an additive-dominance model was appropriate for P. nicotianae isolates Pn Ko1 , Pn Ko2 and Pn Kr1 , which showed low aggressiveness in the two crosses. For the more aggressive isolates Pn Bz1 , Pn Bz2 and Pn Kr2 , epistasis was an integral component of resistance in the two crosses. The presence of epistasis in the resistance of pepper to P. nicotianae was dependent on the level of aggressiveness of the isolates. Selection in pepper with less aggressive isolates was efficient, but not with more aggressive isolates; on the other hand, selection with more aggressive isolates was more stable. The minimum number of genes controlling resistance was estimated at up to 2.71. In the majority of cases, the additive variance was significant and greater than the environmental and dominance variance

Epistasis and genotype-by-environment interaction of grain protein content in durum wheat

Parental, F1 , F 2 , BC 1 and BC 2 generations of four crosses involving four cultivars of durum wheat (Triticum durum Desf.) were evaluated at two sites in Tunisia. A three-parameter model was found inadequate for all cases except crosses Chili x Cocorit 71 at site Sidi Thabet and Inrat 69 x Karim at both sites. In most cases a digenic epistatic model was sufficient to explain variation in generation means. Dominance effects (h) and additive x additive epistasis (i) (when significant) were more important than additive (d) effects and other epistatic components. Considering the genotype-by-environment interaction, the non-interactive model (m, d, h, e) was found adequate. Additive variance was higher than environmental variance in three crosses at both sites. The estimated values of narrow-sense heritability were dependent upon the cross and the sites and were 0%-85%. The results indicate that appropriate choice of environment and selection in later generations would increase grain protein content in durum wheat