Evaluation of Russian wheat aphid resistance in cultivars and advanced lines of wheat under field conditions in Isfahan province, Iran.

Host plant resistance is an economic and environmental friendly method for controlling Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko). To evaluate resistance of 15 cultivars and advanced lines of wheat to RWA under field conditions, an experiment was conducted in a randomized complete block design with 4 replications in Mobarake region (Isfahan province, Iran) during 2001-2003. Four plants were harvested randomly from each plot in a weekly schedule and the numbers of settled aphids per plant were counted for both adults and nymphs, and the damage rate was estimated. Variance analyses were performed on pooled data from all samplings and correlation coefficients among resistance criteria were calculated. Results showed that maximum adult / plant was on Mahdavi, M-78-14, and M-78-19; and minimum adult / plant was on M-73-4, M-73-18, Alvand and M-75-7. Maximum number for nymphs was estimated on M-75-10 and M-78-20 and the minimum number on M-73-4. Mahdavi and M-75-7 had the highest damage rate and M-73-18, M-73-4 and M-78-7 had the lowest. Positive and significant correlation coefficients were found between damage rate with adult aphid / plant, and between the number of adults and nymphs. Therefore, damage rating could be used as a suitable criterion for evaluating resistance of wheat to RWA under field conditions. To assess influence of the pest on yield and yield components, a similar allotment was cultivated and sprayed two times with Metasystox. At harvest, yield and yield components were determined in sprayed and unsprayed allotments, and consequently, the means of yield and yield components between these two allotments were compared using t-student test. The mean comparisons showed that there was no significant difference between sprayed with unsprayed allotments for yield and yield components.