Abstract:
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 variations in the resident RWA populations and evolution of virulent biotypes. To fully exploit host plant resistance (HPR) in management of RWA, resident populations of RWA were evaluated for biotypes in order to develop and deploy cultivars that exhibit cross biotype resistance. Three experiments were conducted in a greenhouse at KARI-Njoro to characterize population dynamics, host choice and virulence of RWA populations from the endemic areas (Eldoret, Mau Narok, Njoro and Egerton) in Kenya. The first experiment sought to determine variations in population characteristics and survivorship of RWA populations on KRWA9 which contains an unknown Dn gene and a susceptible host, Kenya Kwale (Kwale). A factorial experiment was set up in randomized complete block design (RCBD) replicated eleven times. A single, day old nymph was placed on a new fully open leaf in a 0.5mm diameter clear plastic straw leaf cage and observed daily. There was variation in aphid lifespan, reproductive longevity and aphid fecundity between populations. The second experiment was to determine variation in RWA preference for four host genotypes; AUS7 containing Dn4 gene, AUS9 containing Dn7 gene, KRWA9 which contains an unknown Dn gene and susceptible Kwale. This was a factorial experiment in RCBD replicated three times. Results indicate that Kwale, a susceptible variety was the preferred host and Eldoret population had significantly more numbers finding a host as compared to the other populations. The third experiment was a factorial experiment in RCBD replicated three times to determine virulence of the RWA aphids at seedling stage in the greenhouse. Five adult RWA aphids from each RWA location were used to infest four host genotypes; AUS7, AUS9, KRWA9 and Kwale, for 28 days. Results show that Egerton and Njoro populations were more virulent than populations selected from other areas indicating that at least two RWA biotypes exist in Kenya.
