Virulence of some Puccinia triticina races to the effective wheat leaf rust resistant genes Lr 9 and Lr 19 under Egyptian field conditions

Leaf rust (Puccinia triticina Eriks.) is one of the most widespread disease of wheat (Triticum aestivum L.) in Egypt and worldwide. The two leaf rust resistance genes i.e. Lr 9 and Lr 19 were previously highly effective against the predominant Puccinia triticina races in Egypt. In 2015/2016 growing season, susceptible field reaction was recorded on these two genes, where rust severity reached to 40% for Lr 9 and 5% for Lr 19 under Egyptian field conditions at the four locations i.e. El-Behira, El-Minufiya, El-Qalubiya and El-Fayom governorates. In this study, eight leaf rust field samples were collected from these governorates (four from each of Lr 9 and Lr 19). Forty single isolates were derived from the collected samples of Lr 9 and Lr 19 (each with 20 isolates). Eight pathotypes were identified from Lr 9, while only two pathotypes were identified from Lr 19. Also, 39 leaf rust monogenic lines (Lr,s) and 16 commercial wheat cultivars were tested for their seedling reaction against ten leaf rust pathotypes isolated from Lr 9 and Lr 19. While, 12 leaf rust monogenic lines and the same 16 wheat cultivars were evaluated at adult plant stage. The most frequent pathotype (virulent to Lr 9) was KTSPT (30% frequency), followed by TTTMS (25% frequency). The other pathotypes ranged from only 5%-10% frequency. Whereas, the most frequent pathotype (virulent to Lr 19) was CTTTT (85% frequency), but the lowest frequent one was PKTST (15% frequency). Pathotypes i.e. PRSTT, NTKTS and TTTMS (identified from Lr 9) were more aggressive pathotypes on most of the tested leaf rust monogenic lines than others. Also, the two pathotypes; PKTST and CTTTT (identified from Lr 19) were more aggressive pathotypes on most of the tested leaf rust monogenic lines. The leaf rust resistance gene Lr 2a was the most effective gene against almost all of the tested pathotypes at adult plant stage. On the other hand, the three wheat cultivars; Misr 1, Misr 2 and Nubariya 1 proved to be of highly resistance against all of the tested leaf rust pathotypes at adult plant stage.