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Wheat stripe rust is a destructive disease worldwide, caused by Puccinia striiformis f. sp. tritici ( Pst ). Resistance breeding is the most effective method of controlling stripe rust. Xinjiang is a relatively independent epidemic region of wheat stripe rust in China. In recent years, wheat stripe rust in this area has shown an upward trend. Therefore, the purpose of this study was to evaluate the resistance level of wheat cultivars (lines) to the prevalent Pst races and determine the genetic background of stripe rust resistance genes in Xinjiang. Six predominant Pst races in China were used to study resistance of 286 wheat cultivars (lines) at both the seedling stage under controlled conditions and the adult-plant stage under field conditions. In the seedling tests, 175 (61.19%) entries were resistant to the race CYR23, 125 (43.71%) to CYR29, 153 (53.50%) to CYR31, 88 (30.77%) to CYR32, 174 (60.84%) to CYR33, and 98 (34.27%) to CYR34. Among the resistant entries, 23 (8.04%) were resistant to all six races. In the field test, 135 (47.20%) entries were resistant to the tested mixed races. Through comparing the responses in the seedling and adult-plant stages, 109 (38.11%) entries were found to have adult-plant resistance (APR), and 14 (4.90%) entries have all-stage resistance (ASR). The 286 wheat entries were also tested using a wheat breeder chip containing 12 Yr resistance loci. Among these entries, 44 (15.38%) were found to have a single gene, 221 (77.27%) have two or more genes, and 21 (7.34%) have none of the 12 genes, including 144 (50.35%) with Yr30 and 5 (1.75%) with YrSP . Entries with two or more genes have stronger resistance to Pst . Overall, the majority of entries have all-stage and/or adult-plant resistance, but their genes for resistance in addition to the 12 tested Yr genes need to be determined. It is also necessary to introduce more effective resistance genes in the breeding programs to improve stripe rust resistance in wheat cultivars in Xinjiang., Competing Interests: The author(s) declare no conflict of interest.

Stripe rust, caused by Puccinia striiformis f. sp. tritici ( Pst ), is the most destructive fungal disease affecting wheat in China, especially in Shaanxi Province, an important epidemiological region connecting the western Pst over-summer regions and the central and eastern spring epidemic regions in the country. In the present study, 291 Pst isolates from Shaanxi Province were studied for their virulence using two sets of wheat differentials, population structure using single-nucleotide polymorphism (SNP) markers, and sensitivity to fungicide. When the isolates were tested on the Chinese differentials of 19 wheat cultivars, 72 races were identified, which belonged to three groups, including the Guinong 22 group (48.45%), Hybrid 46 group (31.62%), and Suwon 11 group (19.93%). The three most predominant races were CYR34 (15.46%), G22-14 (11.68%), and CYR32 (10.65%). When the isolates were tested on the 18 Yr single-gene differentials, 95 races were identified, but none of the isolates were virulent to either Yr5 or Yr15 . Cluster analyses of the virulence data based on the two sets of differentials and the SNP marker data consistently separated the Shaanxi Pst population into two clusters in the central part and southern part of the Province. Triadimefon sensitivity testing across different concentrations showed a broad range of half-maximal effective concentration (EC 50 ) values, from 0.03 to 5.99 μg mL -1 , with a mean EC 50 of 0.46 μg mL -1 . The majority of isolates (90.72%) were sensitive to the fungicide. The correlation analyses of the virulence, SNP marker, and the triadimefon sensitivity data showed no significant correlations, except a logarithmic relationship between the EC 50 value and the number of avirulence factors. This study is the first to determine the relationship of virulence and SNP markers with triadimefon sensitivity in a regional Pst population.The findings provide valuable insights for breeding resistant wheat cultivars and integrated management of stripe rust.

Stripe rust, caused by Puccinia striiformis f. sp. tritici ( Pst ), is one of the most important diseases of wheat. Identifying Pst races is essential for developing resistant cultivars and managing the disease. In this study, 608 isolates collected from China in 2021 were tested with the Chinese set of 19 wheat variety differentials and the set of 18 Yr single-gene differentials. Of the 119 races detected with the Chinese set of differentials, 94 were new. A higher number (149) of races were identified using the Yr single-gene differentials. The frequencies of virulence factors to 17 of the 19 Chinese differential varieties and to 10 of the 18 Yr single-gene differentials were high (>60%). None of the isolates were virulent to the differentials Zhong 4 ( Yr genes unknown) and Triticum spelta Album ( Yr5 ) in the Chinese set and the Yr5 and Yr15 lines in the single-gene set of differentials, indicating that these genes or varieties are effective against the Pst population detected in 2021. Using Nei's genetic distance, the 16 provincial Pst populations were clustered into six groups based on the Chinese set and eight groups based on the Yr single-gene set of differentials. In addition, we found that the same races identified using the Chinese differentials could be further differentiated into different races using the Yr single-gene differentials, suggesting a higher differential capability than the Chinese set of differentials. The results provide a scientific basis for monitoring Pst populations and guiding resistance breeding in China., Competing Interests: The author(s) declare no conflict of interest.

Wheat leaf rust, caused by Puccinia triticina f. sp. tritici ( Pt ), is distributed widely in wheat-producing areas and results in serious yield losses worldwide. In China, leaf rust has been largely controlled with a demethylation inhibitor (DMI) fungicide, triadimefon. Although high levels of fungicide resistance in pathogens have been reported, no field failure of wheat leaf rust to DMI fungicides has been reported in China. A resistance risk assessment of triadimefon to Pt was investigated in the present study. The sensitivity of 197 Pt isolates across the country to triadimefon was determined, and the density distribution of EC 50 values (concentration at which mycelial growth is inhibited by 50%) showed a continuous multimodal curve because of the extensive use of this fungicide in wheat production, with a mean value of 0.46 μg/ml. The majority of the tested Pt isolates were sensitive to triadimefon, whereas 10.2% developed varying degrees of resistance. Characterization of parasitic fitness revealed that the triadimefon-resistant isolates exhibited strong adaptive traits in urediniospore germination rate, latent period, sporulation intensity, and lesion expansion rate. No correlation was observed between triadimefon and tebuconazole and hexaconazole, which have the similar mode of action, or pyraclostrobin and flubeneteram, which have different modes of action. Overexpression of the target gene Cyp51 led to the triadimefon resistance of Pt . The risk of resistance to triadimefon in Pt may be low to moderate. This study provided important data for fungicide resistance risk management against wheat leaf rust., Competing Interests: The author(s) declare no conflict of interest.

Stripe rust, caused by Puccinia striifomis f. sp. tritici ( Pst ), is one of the most destructive wheat diseases in China. Understanding the interregional dispersal of Pst inoculum is important for controlling the disease. In the present study, wheat stripe rust samples collected from the winter spore production and oversummering regions in November 2018 to March 2019 were studied through virulence testing and molecular characterization. From 296 isolates, 96 races were identified using a set of 19 Chinese wheat cultivars and 111 races were identified using 18 Yr single-gene lines as differentials. The isolates from Hubei province in the winter spore production area had the highest similarity in virulence with those from eastern Yunnan in the oversummering area. Molecular characterization using 13 simple-sequence repeat and 43 Kompetitive allele specific PCR-single nucleotide polymorphism markers supported the conclusion that the Pst populations in the winter spore production regions were from Guizhou and eastern Yunnan, key oversummering areas in the southwest. Furthermore, an analysis of wind movement at the 700-hPa high altitude also supported the conclusion of spore dispersal from the southwestern oversummering region to the south-central winter spore production region. The results of this study provide an epidemiological basis for deploying various effective resistance genes in different regions to control stripe rust.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici ( Pst ), is a destructive disease of wheat that seriously threatens production safety in wheat-producing areas worldwide. In China, the disease has been largely controlled with the fungicide triadimefon. Although high levels of fungicide resistance in other fungal pathogens have been reported, failure to control Pst with any fungicides has seldomly been reported, and fungicide sensitivity of Pst has not been evaluated in China. The distribution of triadimefon-resistant Pst isolates was investigated in the present study. The baseline sensitivity of 446 Pst isolates across the country to triadimefon was determined, and the concentration for 50% of maximal effect showed a unimodal distribution curve, with a mean value of 0.19 μg ml -1 . The results indicated a wide range of sensitivity to triadimefon, with more insensitive isolates collected from Pst winter-increasing areas and northwest oversummering areas, whereas more sensitive isolates were collected from southwest oversummering areas and epidemic areas of Xinjiang and Tibet. The majority of the tested Pst isolates were sensitive to triadimefon; only 6.79% had developed varying degrees of resistance. Characterization of parasitic fitness revealed that the triadimefon-resistant isolates exhibited strong adaptive traits in the urediniospore germination rate, latent period, sporulation intensity, and lesion expansion rate. Positive cross-resistance was observed between triadimefon and tebuconazole or hexaconazole, but not between pyraclostrobin or flubeneteram. The point mutation Y134F in the 14α-demethylase enzyme (CYP51) was detected in triadimefon-resistant isolates. A molecular method (kompetitive allele-specific PCR) was established for the rapid detection of Y134F mutants in the Pst population. Two genotypes with one point mutation Y134F conferred resistance to triadimefon in Pst . The risk of resistance to triadimefon in Pst may be low to moderate. This study provided important data for establishment of high throughput molecular detection methods, fungicide resistance risk management, and the development of new target fungicides.

Stripe rust, caused by Puccinia striiformis f. sp. tritici , is one of the most devastating wheat diseases in Ethiopia. To study virulence genetics of the pathogen, 117 progeny isolates were produced through sexual reproduction of an Ethiopian isolate of the stripe rust pathogen on Berberis holstii plants under controlled conditions. The parental and progeny isolates were characterized by phenotyping on wheat lines carrying single Yr genes for resistance and genotyped using 10 polymorphic simple sequence repeated (SSR) markers. The progeny isolates were classified into 37 virulence phenotypes and 75 multilocus genotypes. The parental isolate and progeny isolates were all avirulent to resistance genes Yr5 , Yr10 , Yr15 , Yr24 , Yr32 , YrTr1 , YrSP , and Yr76 but virulent to Yr1 and Yr2 , indicating that the parental isolate was homozygous avirulent or homozygous virulent at these loci. The progeny isolates segregated for virulence to 12 Yr genes. Virulence phenotypes to Yr6 , Yr28 , Yr43 , and Yr44 were controlled by a single dominant gene; those to Yr7 , Yr9 , Yr17 , Yr27 , Yr25 , Yr31 , and YrExp2 were each controlled by two dominant genes; and the virulence phenotype to Yr8 was controlled by two complementary dominant genes. A linkage map was constructed with seven SSR markers, and 16 virulence loci corresponding to 11 Yr resistance genes were mapped with some loci linked to each other. These results are useful in understanding host-pathogen interactions and selecting resistance genes to develop wheat cultivars with highly effective resistance to stripe rust.

Puccinia striiformis f. sp. tritici (Pst), the stripe rust pathogen infecting cereal crops and grasses, was believed to have a hemicyclic life cycle consisting of uredinial and telial stages before the recent discovery of barberry (Berberis spp.) as an alternate (aecial) host for the fungus. This discovery has improved the understanding of the biology of the stripe rust pathogen. The Himalayan and near-Himalayan regions of Pakistan, China, and Nepal are considered as the center of diversity for Pst pathogen. High genetic diversity has been reported in these areas, probably resulting from the sexual reproduction of the stripe rust fungus. To determine if Berberis species growing in Pakistan are susceptible to Pst, we collected seeds of five species and two subspecies from the Himalayan region in 2016 and inoculated the seedlings with germinated teliospores of a Pakistani Pst isolate under controlled conditions. Pycnia and aecia were produced on all inoculated plants of these species and subspecies, and were demonstrated as Pst by successful infection of wheat plants with aeciospores. This study showed that the tested Pakistani Berberis species and subspecies are susceptible to Pst under controlled conditions.

In recent years, wheat stripe rust caused severe yield losses in western China, especially the Xinjiang Autonomous Region. The population of the stripe rust fungus Puccinia striiformis f. sp. tritici in the vast region had not been well studied. To determine the population structure and compare it with the populations in the neighboring provinces or autonomous regions, P. striiformis f. sp. tritici isolates from Xinjiang, Qinghai, Gansu, Ningxia, and Tibet in western China were characterized by virulence tests with 19 wheat genotypes that are used to differentiate races of P. striiformis f. sp. tritici in China and by genotyping tests with 15 simple-sequence repeat (SSR) markers. In total, 56 races, including 39 previously known and 17 new races, were identified from 308 isolates obtained from the three epidemiological regions covering five provinces, of which 27 previously known and 8 unknown races were detected in Xinjiang, higher than the numbers in either of the other two regions. The races in Xinjiang consisted of those historically and recently predominant races in other regions of China. The P. striiformis f. sp. tritici population in Xinjiang had a higher genetic diversity than populations in other epidemiological regions. Molecular variation among subpopulations within Xinjiang was higher than in other regions. Both virulence and molecular data indicate that the P. striiformis f. sp. tritici population in Xinjiang is related to but more diverse than those in other epidemiological regions. The results show that Xinjiang is an important stripe rust epidemiological region in China, and the information should be useful for control of the disease in the region as well as in other regions.