DETECTION AND CHARACTERIZATION OF THE MECHANISMS OF RESISTANCE TO RUSSIAN WHEAT APHID (HOMOPTERA, APHIDIDAE) IN TALL WHEATGRASS

The Russian wheat aphid, Diuraphis noxia (Mordvilko), is a recently in troduced pest that is an economic threat to wheat, Triticum aestivum L ., and barley, Hordeum vulgare L., production. Tall wheatgrass, Agropy ron elongatum (Host) Beauvois, in an important alternative summer host of the aphid and provides a food source for Russian wheat aphid popul ations between spring harvest and fall planting of cereal crops such a s wheat and barley. Experiments were conducted in the greenhouse to id entify Russian wheat aphid-resistant tall wheatgrass plants obtained f rom the Western Regional Plant Introduction (PI) Station, USDA-ARS, Pu llman, WA. PI 401010 was resistant to leaf chlorosis and leaf curling caused by aphid feeding, and had decreased aphid reproduction compared with 'Jose' tall wheatgrass. Further tests were conducted to characte rize the plant components (antibiosis, antixenosis [nonpreference], an d tolerance) contributing to resistance of PI 401010. PI 401010 had hi gh levels of antibiosis, demonstrated by Russian wheat aphid's delayed reproductive maturity, shorter reproductive lifespan, and reduced rat es of fecundity compared with 2 susceptible genotypes. When infested w ith Russian wheat aphids, plant heights were reduced and dry mass foli age loss per unit of aphid mass produced was high. A strong antixenosi s (nonpreference) resistance component existed in PI 401010 when aphid s were given a choice of several genotypes. PI 401010 is a new source of resistance for germplasm enhancement efforts.