Different types of resistance against greenbug, Schizaphis graminum Rond, and the Russian wheat aphid, Diuraphis noxia Mordvilko, in wheat

A collection of 26 cultivars of wheat Triticum aestivum were screened for r esistance against the two main aphid pests of cereals, the greenbug Schizap his graminum Rond. and the Russian wheat aphid (RWA) Diuraphis noxia Mordvi lko. Since genetic variability has been found in Argentinean populations of both aphid species. this work was aimed at determining the response of dif ferent types of resistance in wheat cultivars when infested with aphids. An tixenosis, antibiosis and tolerance were evaluated with traditional tests i n controlled environmental conditions using a clone of greenbug biotype C a nd a clone of RWA collected on wheat. Genetic resistance was found against one or both aphid species in several wheats. Most of the highest levels of antixenosis, antibiosis and tolerance against the two aphids occurred in di fferent cultivars; as a consequence the resistance mechanisms for both pest s appear to be partly independent. Antibiosis against greenbug or RWA appea rs to be determined by two different sets of genes, one affecting developme nt time and the other reducing fecundity and longevity. The antibiosis agai nst both aphid species in terms of their development time and the intrinsic rate of population increase resulted in a partial cross effect of these ap hid traits against the alternative insect species. Nonetheless, the same cu ltivars affected the total fertility and the longevity of both aphids. Sinc e the highest plant performance levels and the least plant damage were reco rded in different wheats, different patterns of tolerance were displayed ag ainst the greenbug and the RWA. Consequently, different genes appear to be involved in several traits of the resistance mechanisms against the two aph ids. The genes that independently conferred resistance to aphids could be c ombined in new cultivars of wheat to broaden their genetic base of resistan ce against the greenbug and the RWA.