virulence

Wheat stripe rust (Puccinia striiformis f. sp. tritici, Pst) is the most destructive disease of wheat worldwide. Breeding and planting resistant cultivars is the most economic, effective, as well as environmental methods to control the disease. Yunnan is a severe epidemic zone in China, which provides new incursions for other parts of China. Study on virulence of the Pst population and effectiveness of resistance genes, will provide information for breeding and rational use of resistance genes. One hundred and thirty-six136 isolates collected from 9 regions of Yunnan were tested using a set of 18 Yr NILs with genes Yr1, Yr5, Yr6, Yr7, Yr8, Yr9, Yr10, Yr15, Yr17, Yr24, Yr27, Yr32, Yr43, Yr44, YrSP, YrTr1, YrExp2, YrTyTye. Stripe rust races were named by octal code. The results showed that the Pst population in Yunnan is highly variable in races and virulence. A total of 64 races were identified and the top two most frequent races were 550273 (Virulence/Avirulence formula: 1, 6, 7, 9, 27, 43, 44, SP, Exp2, Tye / 5, 8, 10, 15, 17, 24, 32, Tr1 and 550073(Virulence/Avirulence Formula: 1, 6, 7, 9, 43, 44, SP, Exp2, Tye / 5, 8, 10, 15, 17, 24, 27, 32,Tr1), with frequency of 28.68% and 11.76%, respectively. The remaining races had frequencies less than 5.0%. No virulence were found for Yr5, Yr10, Yr15, and Yr32. The frequencies of virulence to Yr24, YrTr1, Yr8, and Yr17 ranged from 0.74% to 11.76%. The frequency of virulence to Yr27 was 52.94%; and virulence to Yr1, Yr6, Yr7, Yr9, Yr43, Yr44, YrSP, YrExp2, and YrTye ranged from 79.94% to 91.91%. The results will guide the breeding and wheat production. (This study was supported by National Natural Science Foundation of China, Grant No. 31260417 and 31560490)

Leaf rust resistance genes Lr9 and Lr19 were previously highly effective against the most predominant races of Puccinia triticina in Egypt. In 2015/2016 growing season, susceptible field reaction was recorded on these two genes where rust severity reached about 40S for Lr9 and 5S for Lr19 under Egyptian field conditions at four locations i.e. El-Behira, El-Minufiya, El-Qalubiya and El-Fayom governorates. Eight leaf rust field samples were collected from these governorates (four from each of Lr9 and Lr19). Forty single isolates were derived from the collected samples of Lr9 and Lr19 (each with 20 isolates). Eight pathotypes were identified from Lr9 and only two pathotypes were identified from Lr19. The most frequent pathotypes virulent to Lr9 were KTSPT (30%) followed by TTTMS (25%). Moreover, the other pathotypes ranged from 5 to 10%. Whereas, the most frequent pathotype virulent to Lr19 was CTTTT (85%) and the lowest PKTST was 15%. Pathotypes i.e. PRSTT, NTKTS and TTTMS identified from Lr9 were more aggressive on most of the tested leaf rust monogenic lines, as they were virulent to 36, 35 and 35 lines, respectively from a total of 39 lines. The two pathotypes; PKTST and CTTTT identified from Lr19 were virulent to 36 and 35 lines, respectively. Moreover, leaf rust pathotypes i.e. NPTNK and PRSTT from Lr9 and PKTST from Lr19 were the most aggressive on the tested wheat cultivars at seedling stage. The Lr2a was the most effective leaf rust resistance genes against the tested pathotypes at adult plant stage. Wheat cultivars Misr 1, Misr 2 and Nubariya 1 were the most resistant cultivars against the tested pathotypes at adult plant stage.

Stripe rust is the most important disease of wheat in Ecuador. Knowledge of race diversity of the pathogen population is limited. Here we present avirulence/virulence phenotypes found in Pst samples collected from wheat between 2001 and 2014. A total of 30 isolates from the Ecuadorian highlands were tested on 15 near-isogenic wheat lines carrying single resistance genes; 21 races were identified. Lines with Yr2, Yr3, Yr26 and Yr27 were not tested in some years. Virulences to Yr1, Yr6, Yr7 and Yr9 were the most frequent (over 70%) in all years, followed by virulence to Yr17 (67%) and Yr27 (53%). Virulence to Yr8 was not found in 2013 and 2014. Virulence to Yr24/Yr26 was present in each year except 2014, although at a low level. Virulence to Yr10 was low. There were some unconfirmed discrepancies from a perfect association of virulences to Yr24/Yr26 and Yr10. Virulence to YrSP increased up to 2013, but was absent in 2014. There was no virulence to Yr5 and Yr15. Despite limited sampling, a diverse population of Pst seems to be present in Ecuador, with virulence for most resistance genes being present. Based on these analyses resistance to Pst in Ecuador could be achieved with Yr5 and Yr15, together with Yr24Yr26, and perhaps YrSP. One possibility for the high pathogenic variation might be sexual recombination on one or more of the 32 Berberis species reported in Ecuador. This needs to be examined along with more intensive sampling from wheat and analysis of the actual resistance genes present in current cultivars.