No abstract

Understanding countrywide pathogen population structure and inter‐epidemic region spread is crucial for deciphering crop potential losses. Wheat stripe rust caused by Puccinia striiformis f. sp. tritici is a destructive disease that affects worldwide wheat production, widespread in China, representing largest epidemic region globally. This study aimed to understand the population structure and migration route of P. striiformis f. sp. tritici across China based on sampling from 15 provinces representing six epidemic zones, viz., over‐summering, over‐wintering, eastern, Yun‐Gui, Xinjiang and Tibet epidemic regions. High genotypic diversity was recorded in over‐summering, Tibet and over‐wintering epidemic regions. Epidemic regions partly explain population subdivision with variable divergence (FST = 0.005–0.344). Xinjiang and Tibet epidemic regions were independent epidemic zones with least sharing of genotypes. Among other epidemic zones, i.e. over‐summering, over‐wintering, eastern and Yun‐Gui epidemic zones, re‐sampling MLGs, clustering‐based structure, DAPC analyses, relative migration and low divergence (FST from 0.006 to 0.073) revealed frequent geneflow. Yun‐Gui epidemic regions, with a potential for both over‐summering and over‐wintering, could play an important role in causing epidemics in main wheat‐cultivating areas of China. High diversity, recombination signatures and inter‐epidemic region migration patterns need to be considered in host‐resistant cultivar development in China and neighbouring countries, considering risk of long‐distance migration capacity of pathogen.

In 2017, a new race (TSA-6) of the wheat stripe rust pathogen, Puccinia striiformis f. sp. tritici, virulent to resistance gene Yr5 were detected in China. However, whether Chinese wheat cultivars are resistant to the new races was unknown. In this study, two isolates (TSA-6 and TSA-9) with virulence to Yr5 were tested on other wheat Yr gene lines for their avirulence/virulence patterns and used, together with prevalent races CYR32 and CYR34 without the Yr5 virulence, to evaluate 165 major Chinese wheat cultivars for their reactions. Isolates TSA-6 and TSA-9 had similar but different virulence spectra, and therefore should be considered as two different races. Their avirulent/virulence patterns were remarkably different from that of CYR34 but quite similar to that of CYR32. Of the 165 wheat cultivars, 21 had all-stage resistance to TSA-6, 34 to TSA-9, and 20 to both races. Adult-plant resistance (APR) was detected in 35 cultivars to TSA-6 and 27 to TSA-9, but only 3 cultivars showed APR to both new races. Slow rusting resistance was observed in 24 cultivars to TSA-6 and of 33 to TSA-9. Analysis of variance (ANOVA) of disease index indicated a significant difference among cultivars, but not among the four races. Based on the molecular marker data, a low percentage of wheat cultivars carried Yr5, Yr7, Yr10, Yr15, Yr26, and/or YrSP. As TSA-6 and TSA-9 can be a serious threat to wheat production in China, monitoring TSA-6, TSA-9, and other races are continually needed.

Identification of Berberis spp. as Alternate Hosts for Puccinia achnatheri-sibirici Under Controlled Conditions and Morphologic Observations of Sexual Stage Development of the Rust Fungus.

Crown rust of barley, caused by Puccinia coronata var. hordei (Pch), was first reported by Jin and Steffenson in 1992, and the fungus has been reported only in the United States and Hungary. In China, stripe, stem, and leaf rusts have been reported on barley, but not for crown rust. Recently, a sample (HZJ0004) of rust collected from barley in Qilian county, Qinghai, China, appeared different from the three rusts based on color, size, arrangements of uredinia and/or telia. Teliospores had crown-shaped appendages on the top. Based on the disease symptoms and morphology of urediniospores and teliospores, the fungus was identified as Pch. Using the internal transcribed spacer sequences, the isolates HZJ0004 from barley and POR3 from buckthorn (Rhamnus sp.) were clustered in one clade with Pch isolates from barley and Elymus repens but in a different clade from the isolate POC8 from wild oat and the varieties of P. coronata from oats and grasses. At the seedling stage, most of the tested cultivars of barley and rye were susceptible to Pch isolates HZJ0004 and POR3, but the cultivars of oats, triticale, wheat, and the most grasses of Aegilops, Brachypodium, Bromus, Calamagrostis, Deschampsia, Elymus, Festuca, and Phleum were resistant, indicating their host specialization on barley. This is the first report of crown rust on barley in China.