Identification of Stripe Rust Resistance Genes in Common Wheat Cultivars From the Huang-Huai-Hai Region of China.

Wheat stripe (yellow) rust, caused by Puccinia striiformis f. sp. tritici (Pst), is a serious fungal disease worldwide, especially in the Huang-Huai-Hai region, a main wheat production area in China. Gene postulation, molecular testing, and pedigree analysis were conducted to determine the presence of stripe rust resistance genes to 15 Pst races in 66 selected commercial wheat cultivars released from 2000 to 2016. In addition, races CYR32, CYR33, and CYR34 were used to evaluate resistance to Pst at the adult-plant stage of wheat in the field. Four Yr genes (Yr9, Yr10, Yr26, and Yr32) were postulated in 24 wheat cultivars either singly or in combination. Thirty-six cultivars might contain unknown Yr genes, whereas no identified Yr gene was postulated in six cultivars. Yr9 was detected at a frequency of 28.8%, and no cultivars carried Yr5, Yr15, or Yr18. Ten cultivars (15.2%) exhibited adult-plant resistance in the field tests with three predominant races. Three cultivars (Langyan 43, Xinong 889, and Yunfeng 139) had all-stage resistance. These results are useful to growers selecting cultivars and to breeders aiming to use more resistance genes to develop new cultivars with effective resistance in order to reduce stripe rust damage.

High Relative Parasitic Fitness of G22 Derivatives is Associated with the Epidemic Potential of Wheat Stripe Rust in China.

In total, 13 commercial wheat cultivars around China and four races of Puccinia striiformis f. sp. tritici (namely, CYR32, CYR33, G22-9, and G22-14) were employed for a test of relative parasitic fitness (RPF) using the drop method. The RPF values were measured, including the urediniospore germination rate, the latent period, the uredinial length, the uredinial density, the infection area, the sporulation intensity, the lesion expansion speed, and the sporulation period. The results indicated that the parameters of relative parasitic fitness of the four P. striiformis f. sp. tritici races on the 13 wheat cultivars were significantly different (P = 0.00) in sporulation intensity, lesion expansion speed, uredinial length, sporulation period, uredinial density, and latent period. The urediniospore germination rates of the four P. striiformis f. sp. tritici races for the test were significantly different (P = 0.00), whereas no correlation with the different cultivars was observed (P = 1.00). The infection areas of the tested races on the different cultivars were significantly different (P = 0.00) but there were no obvious manifestations among the various races (P = 0.20). Principal component analysis (PCA) showed that the sporulation intensity represented sporulation capacity and scalability, the latent period indicated infection ability, and the urediniospore germination rate represented urediniospore vigor, all of which fully contributed to the RPF in the interaction of the four races and 13 wheat cultivars, which was calculated by the following formula: RPF = (sporulation intensity × urediniospore germination rate)/latent period. The sporulation and infection of G22-9 on the 13 large-scale cultivated cultivars were the highest, and the RPF of G22-9 was higher than that of the predominant races, CYR32 and CYR33. This result suggested that G22-9 could become a new predominant race and potentially cause epidemics of wheat stripe rust in China. To prevent potential epidemics, susceptible wheat cultivars should be withdrawn from production and breeding programs should reduce the use of Yr10 and Yr26 and use other more effective resistance genes in combination with nonrace-specific resistance for developing wheat cultivars with durable resistance to stripe rust.