Molecular mapping and markers for leaf rust resistance gene Lr24 in CIMMYT wheat line 19HRWSN-122

Abstract

Leaf rust, caused by Puccinia triticina, is an important foliar disease of wheat (Triticum aestivum L.) worldwide. In the present study, CIMMYT line 19HRWSN-122 and 36 lines with known Lr (leaf rust resistance) genes were inoculated with 13 Chinese P. triticina pathotypes for postulation of Lr genes at the seedling stage. Line 19HRWSN-122 showed high resistance to all 13 P. triticina pathotypes in the greenhouse, indicating that it carries effective seedling resistance. This may be due to a resistance gene combination, an effective gene to all pathotypes present in China or a new resistance gene. With the objective of mapping the putatively new gene for resistance to leaf rust, 20 F1, 280 F2 plants and 254 F2:3 lines from the cross 19HRWSN-122 × Zhengzhou 5389 (susceptible) were inoculated with P. triticina pathotype THJP in the greenhouse. Results based on the F1, F2 and F2:3 lines indicated that a single dominant gene, temporarily designated LrHR122, was present in 19HRWSN-122. Bulked segregant analysis was performed on equal amounts of genomic DNA from ten resistant and ten susceptible F2:3 lines. Molecular markers polymorphic between the resistant and susceptible bulks were used to genotype F2:3 lines. LrHR122 was linked to one SSR marker, one STS marker, one SCAR marker and three EST markers on chromosome 3DL. Marker SCS1302 609 co-segregated with LrHR122, and the closest flanking markers were BE442875 and STS24-16 at genetic distances of 0.4 and 0.4 cM, respectively. Lr24 is known to be located on chromosome 3DL near LrHR122. In seedling tests, lines with both LrHR122 and Lr24 showed high resistance to all 13 Chinese P. triticina pathotypes. According to the pedigree and chromosome position LrHR122 should be Lr24. Lr24 was closely linked to one SSR marker and three EST markers in the terminal region of 3DL. These markers should be useful for marker assisted selection in breeding leaf rust resistant wheat cultivars.