Population Genetic Structures of Puccinia striiformis f. sp. tritici in the Gansu-Ningxia Region and Hubei Province, China.

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.

De novo transcriptome assembly, polymorphic SSR markers development and population genetics analyses for southern corn rust (Puccinia polysora).

Southern corn rust is a destructive maize disease caused by Puccinia polysora Underw that can lead to severe yield losses. However, genomic information and microsatellite markers are currently unavailable for this disease. In this study, we generated a total of 27,295,216 high-quality cDNA sequence reads using Illumina sequencing technology. These reads were assembled into 17,496 unigenes with an average length of 1015 bp. The functional annotation indicated that 8113 (46.37%), 1933 (11.04%) and 5516 (31.52%) unigenes showed significant similarity to known proteins in the NCBI Nr, Nt and Swiss-Prot databases, respectively. In addition, 2921 (16.70%) unigenes were assigned to KEGG database categories; 4218 (24.11%), to KOG database categories; and 6,603 (37.74%), to GO database categories. Furthermore, we identified 8,798 potential SSRs among 6653 unigenes. A total of 9 polymorphic SSR markers were developed to evaluate the genetic diversity and population structure of 96 isolates collected from Guangdong Province in China. Clonal reproduction of P. polysora in Guangdong was dominant. The YJ (Yangjiang) population had the highest genotypic diversity and the greatest number of the multilocus genotypes, followed by the HY (Heyuan), HZ (Huizhou) and XY (Xinyi) populations. These results provide valuable information for the molecular genetic analysis of P. polysora and related species.

Diversity in Puccinia striiformis populations causing the 2013 yellow rust epidemics on major wheat cultivars of Pakistan.

Wheat yellow/stripe rust pathogen Puccinia striiformis is highly diverse and recombinant in the north of Pakistan in the Himalayan region. However, little is known about the role of this diversity in disease epidemics in areas where wheat yellow rust is an important disease in both irrigated and rain-fed wheat (i.e., in the plains of Pakistan). We explored the population diversity in P. striiformis during the rust epidemics of 2013 in the major wheat-growing regions of Pakistan (the Himalayan region, central Khyber Pakhtunkhwa [KP], southern KP, central and northern Punjab). Disease severities among commonly grown cultivars ranged from 5% to 100%. Microsatellite genotyping with 16 simple sequence repeat (SSR) markers revealed a high diversity among 266 isolates collected during the season, with the Simpson diversity index (Simpson 1949) ranging from 0.870 (Himalayan) to 0.955 (southern KP). The recombination signature was stronger in the Himalayan population and central KP compared with wheat-growing regions of Punjab and southern KP. The overall diversity was higher in Pakistan relative to the clonal populations present in Europe, Australia, and the Americas. Analyses of population subdivision revealed no clear evidence of spatial structure for samples from Pakistan, with a maximum fixation index (FST) value of only 0.10. The lack of clear population subdivision could be attributed to migration of pathogen. In turn, the high diversity of P. striiformis in Pakistan represents a potential threat to wheat production in the region and worldwide, as a possible source to found clonal populations in diverse wheat-growing areas.