Evaluation of relative Antibiosis resistance to English grain aphid (Sitobion avenae (F.)) in commercial varieties and developted lines of dryland durum and bread wheats in cold conditions.ý

English grain aphid is one of the most important and periodical pests of small grain cereals, especially wheat, in many regions, particularly Europe and tropical areaes and has been known as the most important pest of the winter wheats, causing direct damages on them in the spring. The aphid is the dominant species amongst the cereal aphid species in Iran. In recent years, it's outbreaks have been reported world-widely and from some regions of Iran e.g. Golestan, Moghan and Fars, resulting considerable reductions in crop yields. The probable potential of the aphid outbreaks in some regions of the country, demands studies on evaluation of resistance or susceptibility of wheat cultivars commonly planted in dry and hiland regions at their different growth stages. For this purpose, an investigation was made on relative resistance of 10 bread and 4 Durum wheat cultivars to English grain aphid. The study was conducted in a completely randomized blockes design with 10 treatments each with 20 replicates for bread wheats and 4 treatments each with 20 replicatesat for durum wheats during years 2009 til 2011. The survival rate of the nymphs, their developmental time, adult fecondity and the relevant rate of natural population increase (rm value) within the first 15 days of reproductive period, at three tillering, stem elongation and heading growth stages of the plants was calculated. ANOVA of the results based on two factorial experiments (10 3) and (4 3) with two factors, variety and growth stage, indicated highly significant differences (P0.01) between the varieties, growth stages and their interactions. Comparison of means using Duncan s multiple range test (P0.01) for bread wheats, showed the Azar2 variety causing the longest nymphal maturation time, the lowest mean number of offsprings produced during the 10 days of reproductive period, the rm value (0.259) and mean developmental time, was ranked in the first group whilst the Rasad resulting in were included in group 10 (rm=0.340). Thus, it can be declaired that Rasad is regarded as the suitable plant for this pest and regarded as the susceptible cultivar to English grain aphid. Azar2 is resistant to the aphid in comparison to the other varieties. Also for durum wheats Comparison of means using Duncan s multiple range test (P0.01), showed the Cheheldaneh variety causing the longest nymphal maturation time, the lowest mean number of offsprings produced during the 10 days of reproductive period, the rm value (0.294) and mean developmental time, was ranked in the first group whilst the Gardish resulting in were included in group 4 (rm=0.329). Thus, az same az bread wheats, it can be declaired that Gardish is regarded as the susceptible cultivar to English grain aphid and Cheheldaneh is resistant to it in comparison to the other varieties. Comparison of the means made on data obtained from the growth stages of the rearings on the plants showed that at the heading stage, the adverse effects of feeding on different cultivars on the studied aphid s biological features, decreased and rearing conditions regarding food quality, had beneficial effects for the aphid. Comparison of means of interaction effects of cultivars and their growth stages, also showed that food preferences of the English grain aphid varied on the different varieties and at two growth stages.