Introgression of Leaf Rust and Stripe Rust Resistance Genes from Aegilops Umbellulata to Hexaploid wheat Through Induced Homoeologous Pairing

Abstract

First alien leaf rust resistance gene Lr9 was transferred from Ae. umbellulata into hexaploid wheat in the year 1956 through irradiation induced translocation. A number of other genes were subsequently transferred from non-progenitor and progenitor Aegilops species and exploited commercially. However, the appearance of new virulences neces- sitates the search of novel sources of rust resistance. An Ae. umbellulata acc. 3732 was found to be resistant to several wheat diseases such as leaf rust, stripe rust, Karnal bunt, powdery mildew and cereal cyst nematode. An amphiploid (AABBUU) synthesized from the cross of Ae. umbellulata acc. 3732 and T. durum cv. WH890 was crossed to CS PhI forrust resistance has been transferred to hexaploid wheat. The introgression lines were analysed with SSR markers for identifying the introgressed regions. The introgressions were detected for chromosomes of homoeologous group 2, 4 and 5. Bulk segregant analysis is in progress to identify the SSR markers segregating with resistance inducing homoeologous pairing between Ae. umbellulata and wheat chromo- somes. The F1 (AABBDU) was crossed to a susceptible hexaploid wheat cv. WL711 and introgression lines carrying resistance to leaf and stripe rust were selected in backcross progenies. The BC2F1 plants with leaf and stripe rust resistance genes were selfed, and homozygous lines with least linkage drag were selected and screened against five leaf rust and three stripe rust pathotypes. The introgression lines were resistant to all the leaf rust pathotypes and stripe rust pathotypes. Transfer of Lr9 was ruled out by screening the introgression line with 77-7, virulent on Lr9. For studying the inheri- tance of transferred rust resistance genes, an F2 population was generated by crossing the introgression line with the recipient parent WL711. Screening of F2 population at the seedling stage against leaf rust pathotype 77-5 revealed that a single dominant gene governs the resistance at seedling stage. The F2 plants screened at the seedling stage were grown in the field and screened at adult plant stage against a mixture of pathotypes under artificial epiphytotic conditions. All plants that were resistant at the seedling stage maintained resistance at adult plant stage. Out of a total of 48 susceptible seedlings, 28 showed resistance at adult plant stage indicating the presence of adult plant resistance (APR) gene as well. The population segregated for two genes for leaf rust, one seedling and one APR, with a 2 (15:1) of 12.5. Thus from Ae. umbellulata, two novel leaf rust resistance genes(one seedling resistance and one APR) and stripe