Wheat stripe rust, caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst), is a destructive wheat disease in China. The Gansu–Ningxia region (GN) is a key area for pathogen over-summering in China, and northwestern Hubei (HB) is an important region for pathogen over-wintering, serving as a source of inoculum in spring epidemic regions. The spatiotemporal population genetic structure of Pst in HB and the pathogen population exchanges between GN and HB are important for estimating the risk of interregional epidemics. Here, 567 isolates from GN and HB were sampled from fall 2016 to spring 2018 and were genotyped using simple sequence repeat markers. The genotypic and genetic diversity of Pst subpopulations in HB varied among seasons and locations. Greater genetic diversification levels were found in the spring compared with fall populations using principal coordinate analysis and Bayesian assignments. In total, there were 17 common genotypes among the 208 determined, as shown by a small overlap of genotypes in the principal coordinate analysis and dissimilar Bayesian assignments in both regions, which revealed the limited genotype exchange between the populations of GN and HB.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive wheat diseases worldwide. Understanding the effects of cultivar mixture on disease control and population genetic structure of Pst could promote the effective application of cultivar mixtures. This study designed nine cultivar mixtures composed of different component cultivars with field experiments in Zitong County, Sichuan Province in two seasons from 2016 to 2018. Diseased leaves were collected in each plot of treatment in the spring and, in total, 835 and 568 isolates were obtained and genotyped with 10 pairs of simple sequence repeat markers in the 2 years, respectively. The observed and theoretical values of the area under the disease progress curve (AUDPC), wheat yield, Pst genotypic diversity, and the frequency of Pst dominant genetic groups were compared among cultivar mixtures. With the 2 years’ experiments, there were three and two cultivar mixtures, respectively, showing significant effect on the relative reduction of AUDPC; there were no significant effects on the relative yield increase in all mixtures in the 2 years. There were four and five cultivar mixtures showing positive effects on the relative increase of Pst genotypic diversity in the 2 years, respectively. Moreover, all cultivar mixtures could decrease the frequencies of Pst dominant genetic groups on highly susceptible component cultivar compared with their theoretical frequencies. [ ] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Tomato (Solanum lycopersicum) gray leaf spot disease is a predominant foliar disease of tomato in China that is caused mainly by the necrotrophic fungal pathogen Stemphylium lycopersici. Little is known regarding the pathogenic mechanisms of this broad-host-range pathogen. In this study, a comparative transcriptomic analysis was performed and more genetic information on the pathogenicity determinants of S. lycopersici during the infection process in tomato were obtained. Through an RNA sequencing (RNA-seq) analysis, 1,642 and 1,875 genes upregulated during the early infection and necrotrophic phases, respectively, were identified and significantly enriched in 44 and 24 pathways, respectively. The induction of genes associated with pectin degradation, adhesion, and colonization was notable during the early infection phase, whereas during the necrotrophic phase, some structural molecule activity-related genes were prominently induced. Additionally, some genes involved in signal regulation or encoding hemicellulose- and cellulose-degrading enzymes and extracellular proteases were commonly upregulated during pathogenesis. Overall, we present some putative key genes and processes that may be crucial for S. lycopersici pathogenesis. The abilities to adhere and colonize a host surface, effectively damage host cell walls, regulate signal transduction to manage infection, and survive in a hostile plant environment are proposed as important factors for the pathogenesis of S. lycopersici in tomato. The functional characterization of these genes provides an invaluable resource for analyses of this important pathosystem between S. lycopersici and tomato, and it may facilitate the generation of control strategies against this devastating disease.

Cucumber (Cucumis sativus L.) is an important vegetable. China's annual output exceeds 50 million tons, accounting for more than 40% of the world total. In Nov 2021, a wilt disease was observed on cucumber plants in Beiluo Town, Shouguang, Weifang City, Shandong Province, China (36°88'N, 118°74'E). The incidence across the greenhouses (≈0.13 ha) was approximately 25%. Leaves of plants in the field turned yellow and wilted. Finally, the whole plant withered and died. The base of the main vine stem shrank and the epidermis cracked longitudinally. Tissue fragments from infected stem bases (5 mm × 5 mm) were surface disinfected with 0.1% mercuric chloride solution for 30 s, followed by 75% ethanol for 30 s, and then washed three times with ddH₂O. These sections were then placed onto PDA and incubated at 25 ± 2°C for five days. Twelve strains (similar colony morphology) belonging to fungal species were obtained from 10 disease samples. On PDA, the colonies appeared off-white or light-orange, occasionally with radiating wrinkles, a damp surface, and defined margins. The conidiophores were solitary, unbranched or rarely irregularly branched, transparent, smooth-surfaced, and thin-walled. Sporulation cells (bottle-stem type autotrophic hyphae) extended with a transparent, smooth surface, a slightly wider base, and a pointed top. Typically, they were solitary upright bottle-necks, 6.3-24.3 μm × 1.4-3.3 μm (n = 30). The conidia aggregated into a head-shaped, oval, shaped, or round shape with narrow ends and a wide middle, transparent, smooth-surfaced, with thin walls and 0-1 septa, containing oil globules. The size of conidia ranged from 4.0-8.9 μm × 2.0-4.0 μm. These morphological characteristics were similar to those of Plectosphaerella sp. At the same time, the internal transcriptional spacer (ITS), and the large subunit (LSU) of the 28S rRNA gene were amplified and sequenced using the primer pairs ITS1/ITS4 and LR5/LROR (Giraldo et al., 2019). BLASTn analysis, the obtained sequences of the ITS amplicon (OR994322), and the LSU domain amplicon (PP092994) showed 99.80% (507/508 bp) and 97.21% (872/897 bp) identity to sequences of P. cucumerina isolates OP881967.1 and MK143394.1, respectively, in the NCBI database. A multilocus phylogenetic tree constructed by MEGA 11 software showed that the representative isolates were assigned to the group of P. cucumerina. To confirm their pathogenicity, 10 ml of spore suspension (105 spores/ml) were poured onto the rhizomes of seedlings (1-2 leaf stage; 20 plants per strain). Another 20 seedlings treated with sterile distilled water were used as the control. Each trial was performed three times. Seedlings inoculated with P. cucumerina began to show symptoms on the 5th day, which continued until the 21st day after inoculation. The symptoms were similar to those observed in the diseased plants in the field. The control seedlings showed no symptoms. P. cucumerina was re-isolated from inoculated diseased seedlings with 100% homology, whereas no fungal growth was observed from the control seedlings. The results indicate that P. cucumerina was the pathogen of cucumber blight. So far, More than 10 species of plants, including Brassica oleracea and Foeniculum vulgare, are known hosts of P. cucumerina in China (Li et al.2017, Su, et al. 2017). This is the first report of P. cucumerina causing wilt on C. sativus L. (Lei et al., 2017). Our study laid a critical foundation for the prevention and control of this disease on cucumbers in China.