Development and Characterization of Wheat Germplasm with Combined Resistance to Russian Wheat Aphid and Stem Rust (Race “Ug99”) in Kenya

Abstract

Wheat is the second most important cereal in Kenya. However, production is severely constrained by both abiotic and biotic stresses. Of the biotic stresses a devastating pest ( Russian wheat aphid (RWA)) and a serious disease ( stem rust race TTKS (“Ug99”)) are currently the biggest problem for wheat producers in Kenya. Severe infestations by RWA may result in yield losses of up to 90% while “Ug99” infected fields may suffer 100% crop loss. The two pests combined are seriously affecting wheat farmers’ incomes because of the heavy reliance on pesticides that increase the cost of production. This study attempted to develop and characterize wheat lines that are resistant to both RWA and “Ug99” by pyramiding two major resistance genes. Three wheat varieties: “ Kwale ” , a Kenyan high yielding variety but susceptible to both RWA and “Ug99”; “ Cook ” , an Australian variety carrying stem rust resistance gene Sr 36 conferring immunity to “Ug99”; and “ KRWA9 ” , a Kenyan line with resistance to RWA but of poor agronomic attributes were used. A double cross F 1 (DC F 1 ) was obtained by crossing the F 1 of “ Kwale × Cook ” and the F 1 of “ Kwale × KRWA9 ” . The DC F 1 population was subjected to sequential screening for both RWA and “Ug99” resistance. Surviving DC F 1 progenies were left to self pollinate to obtain the F 2 of the double cross (DC F 2 ). The DC F 2 progenies were sequentially screened against RWA and “Ug99” to yield a population that was resistant to both RWA and “Ug99”. Genotyping of the DC F 2:3 families were conducted to select homozygous resistant plants. Data indicated that the RWA and “Ug99” resistance genes were successfully pyramided. Though races with virulence for Sr 36 have been reported, the gene provides immunity to race “Ug99” and can still be effectively used as a component for “Ug99” resistance breeding together with other Sr genes .