Virulence of Russian Wheat Aphid, Diuraphis Noxia (Kurdjumov) (Homoptera: Aphididae) Populations in Kenya

The Russian wheat aphid (RWA) Diuraphis noxia (Kurdjumov) is a serious pest of wheat in Kenya. Development and use of RWA resistant wheat (Triticum aestivum L.) varieties, has been constrained by RWA populations evolving with differential virulence to given resistant host plants. To fully exploit host plant resistance (HPR) in management of RWA, local populations of RWA have to be evaluated for differential virulence and biotypes in order to develop and deploy cultivars that exhibit cross biotype resistance. A study was conducted at KARI-Njoro to characterize virulence of RWA populations from the endemic areas (Eldoret, Mau Narok, Njoro and Egerton) in Kenya. A factorial experiment in randomized complete block design replicated three times was set up to evaluate seedling resistance to RWA with variety and aphid collection source as main factors in the screen house. Five adult RWA aphids from each of the four collection locations were used to infest four host genotypes; PI624933-1 containing Dn4 gene, 2414-11-2 containing Dn7 gene, KRWA9 which contains an unknown Dn gene and a susceptible check, K.KWALE, for 28 days to determine virulence of the RWA aphids to seedlings of the four wheat genotypes in the greenhouse. Data was recorded on damage scores, plant height, plant height reduction, shoot biomass and biomass reduction of test plants 28 days after infestation. Results of an analysis of variance of these plant parameters show that Egerton population was more virulent than populations selected from other areas as it caused more damage on resistant lines. Keywords: Diuraphis noxia, biotype, virulence, RWA, Wheat.