Development Of SSR And AFLP Markers For Leaf Rust Resistance Gene Lr19 In Wheat

Leaf rust caused by Puccinia recondita f. sp. tritici is a very serious and the most widely distributed disease of wheat. Using resistant cultivars is an economic and environmental-friendly way for minimizing the losses caused by the disease. As an important leaf rust resistance gene, the Lr19 was firstly transferred into the wheat genome from Thinopyrum sp. in the form of the substitution line 'Agrus' in 1966. At present, Lr19 was great potential to be used for wheat production. The complete linkage or tightly linkage markers of Lr 119 are very important to isolate and use the resistant gene.The gene is located on chromosome 7DL. SSR and AFLP were employed to develop molecular markers for the gene. For the development of SSR markers, the DNAs were extracted from the resistant line ThatcherLr19 (TcLr19), the susceptible line Thatcher, five TcLr19 near-isogenic lines (NIL), and a population of 120 F₂ plants derived from a cross of TcLr19 with Thatcher, respectively. Then, they were amplified with 13 microsatellite primer pairs. Two of the primer pairs detected a polymorphism between the parent plants. One of them, the SSR marker Xgwm44_139bP, was tightly linked at a distance of 0.9 cM with the resistance gene Lr19.Amplified fragment length polymorphism (AFLP) analysis was carried out in TcLr19, Thatcher, other 23 wheat leaf rust risistance near-isogenic lines, and the F₂ generation from corossing between TcLr19 and Thatcher respectively. Seven markers linked to Lr19 were obtained and were named as: P-AGT/M-GAG_289bp(3.3 cM), P-ACA/M-GGT_102bP(4.1 cM), P-ACA/M-GGT_106bp(4.1 cM), P-Aac/M-cag_123bp (4.9 cM), P-AAC/M-GGT_203bP (5.0 cM), P-ACA/M-GGT_290bP(5.7 cM), and P-ATC/M-GAG_293bP(9.6 cM), respectively. The closest marker was mapped within 3.3 cM to Lr19. The leaf rust resistance gene Lr19 was flanked on either side by the marker P-AAC/M-GGT_203bp(5.0 cM) and other six markers. All of these specific fragments from both SSR and AFLP were isolated from the polyacrylamide gels, re-amplified, cloned and sequenced.