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 geneLr9was transferred fromAe. umbellulatainto hexaploid wheat in the year 1956 through irradiation induced translocation. A number of other genes were subsequently transferred from non-progenitor and progenitorAegilopsspecies and exploited commercially. However, the appearance of new virulences necessitates the search of novel sources of rust resistance. AnAe. umbellulataacc. 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 ofAe. umbellulataacc. 3732 andT. durumcv. WH890 was crossed to CS PhI for inducing homoeologous pairing betweenAe. umbellulataand wheat chromosomes. 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 ofLr9was ruled out by screening the introgression line with 77-7, virulent onLr9. For studying the inheritance of transferred rust resistance genes, an F2population was generated by crossing the introgression line with the recipient parent WL711. Screening of F2population at the seedling stage against leaf rust pathotype 77-5 revealed that a single dominant gene governs the resistance at seedling stage. The F2plants 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 χ 2 (15:1) of 12.5. Thus fromAe. umbellulata, two novel leaf rust resistance genes(one seedling resistance and one APR) and stripe rust 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