Resistance categories of synthetic hexaploid wheats resistant to the Russian wheat aphid (Diuraphis noxia)

Six Russian wheat aphid (RWA;Diuraphis noxia Mordvilko)-resistant synthetic hexaploid wheats derived from interspecific crosses between Triticum dicoccum Schrank. and Aegilops tauschii (Coss.) Schmal. were evaluated for the three major resistance categories: antibiosis, antixenosis, and tolerance. Aphids on synthetic hexaploids took a significantly longer time to reach maturity than aphids on the susceptible bread wheat control 'Seri M82', but no differences were observed for daily nymph production or intrinsic rate of increase. The antixenosis test showed that the synthetic hexaploids attracted significantly fewer aphids than Seri M82, and pubescent leaves may contribute to the antixenotic properties in these synthetic hexaploids. No significant differences were observed for growth reduction in the tolerance test, although Seri M82 had the highest reduction in the experiment. A plant resistance index revealing differences among the synthetic hexaploid wheats indicates genetic diversity for RWA resistance. The plant resistance index can aid plant breeders in selecting the best germplasm for incorporating Russian wheat aphid resistance into elite bread wheat lines. Of the synthetic hexaploids, CWI 76621 and CWI 76629 showed the highest levels of resistance overall, and are thus potential candidates for Russian wheat aphid resistance breeding.