Postulation Of Stripe Rust Resistance Genes In Chinese Commercial Wheat Varieties And Parasitic Fitness Of A New Race In China

Puccinia striiformis f.sp. tritici (PST), a casual agent of wheat stripe rust, has historically caused epidemic many times in China and continuously threaten Chinese wheat production. Resistant cultivars are the most efficient and environmentally friendly method for reducing damage caused by stripe rust. However, PST is notoriously known for its ability to adapt to and become virulent against cultivars with specific resistance genes when these cultivars are widely used. Because of a new race V26 appeared, it will portentially pose an increased threat to wheat production in some regions of China. Many of the Yellow rust resistance genes (Yr genes) in Chinese wheat cultivars were still unknown. It is imperative to definitude stripe rust resistance genes in major commercial wheat cultivars. and parasitic fitness of the new race, which was useful for forecasting of the predominant races in the near future and rational and effective utilization of these stripe rust resistance genes in China.Twenty one isolates of Puccinia striiformis f.sp. tritici with different virulence profile from several parts of the world were used to postulate Yr genes in 115 Chinese wheat cultivars. The studies detected Yr1,Yr2+Yr6,Yr2+YrHâ…¦,Yr3+YrND,Yr4+YrH46,Yr5,Yr6,Yr8,Yr9,Yr10,Yr12,Yr15,Yr17,Yr26,Yr27,Yr25+YrSD,YrSu either singly or in combinations in 78 cultivars. The resistance genes Yr1 was found in 7 cultivars such as Yumai18, etc; Yr1 and Yr9 were detected simultaneously in 36 cultivars in combination with uncharacterized Yr genes or Yr2+YrHâ…¦and Yr8; Yr2+YrHâ…¦was detected in Chang4640 and Chang6878; Jinan17 may carried Yr3+YrND; Yr4+YrH46 was postulated in Lantian18; Yr2+Yr6 was found in Chuannong19; Yr5 or Yr10 was postulated in Lantian22; Yr26 was found in Chuanmai42 and Lantian17; Zhongliang99293 and Zhongliang200192 were postulated to carry Yr26 or Yr10+Yrmor; Zhengnong16 and Jinmai54 may carry Yr12; Yr25+YrSD was detected in 4 cultivars such as Xiaoyan22; 7 cultivars were postulated to carry Yr15 such as Lantian21 etc; Yr27 was postulated in 6 cultivars such as Wanmai19 etc; Chuanmai39 may carry Yr6; Yr17 was determined in Luohan2 and Pingan6; YrSu was postulated in 3 cultivars such as Gaoyou503 etc.Race CYR32, CYR33 and isolate V26 were used to identify the resistance of 115 Chinese wheat varieties to stripe rust at adult plant stages. As the results indicated that 13 cultivars appeared to have all stage resistance, such as Zhoumai17, Lumai1 etc; 5 cultivars appeared to have adult plant resistance to all the 3 races such as Yumai34 etc; while 3 cultivars appeared to have slow stripe resistance, Lumai 23, Jinmai 54, Shan 229. Overall, the resistance level of current Chinese wheat to stripe rust was still low.Six predominant commercial wheat varieties were used to determine the parasitic fitness of race CYR32, CYR33 and isolate V26 at the seedling stage. A total of 9 parameters in the disease development process were tested, and the data were analyzed by multivariate ANOVA (ANalysis Of VAriance) of SPSS 16.0. The results indicated that 3 parameters showed significant differences between races and varieties such as spore germination rate etc.3 parameters showed a statistically non-significant trend between races, but significance between varieties such as chlorisis number, etc. While 3 parameters were no significant differences among cultivars, but significant differences between races such as sporulation time etc.The data analysis by principal component analysis (PCA) showed that the aggressiveness displayed high positive correlation with sporulation and development capacity of PST, which was attributed to spore germination rate, latent period, lesion expansion rate, sporulation intensity, pustule density and sporulation coverage. The second important component for parasitic fitness was infectivity, attributed to chlorisis number, infection probability and uredium length. According to these models, race CYR32, isolate V26, and CYR33, displayed the decreasing tendency about the relative parasitic fitness, which showed it was possible that the frequency of virulence to Yr26 could increase rapidly in the near future.