Breeding resistant wheat (Triticum aestivum) cultivars is the most efficient way to manage wheat stripe rust, a highly destructive disease caused by the fungal pathogen Puccinia striiformis f. sp. tritici (Pst). Therefore, the exploration of new resistance genes is ongoing. The resistance gene Yr85 confers protection against predominant Pst races in China at all stages of plant development. Here, we fine-mapped Yr85 to a 0.12 cM interval between allele-specific quantitative PCR markers XK1B-61 and XK1B-65, corresponding to a 1.76 Mb region on chromosome 1BS in the IWGSC RefSeq v2.1 reference genome (wheat cultivar Chinese Spring), using 5507 F₅ plants derived from heterozygous F₄ plants, themselves descendants of an AvS × AvSYr85NIL cross. Haplotype analysis and whole-genome resequencing suggested that Yr85 may be from a distant source. Moreover, agronomic trait evaluation indicated that Yr85 is located in a chromosomal region lacking linkage drag. Genotyping of 309 Chinese wheat cultivars and lines with a marker that cosegregated with Yr85 during fine mapping identified one cultivar possibly carrying the resistance gene. Our findings indicate that Yr85 has potential for use in wheat-breeding programs in China. This study lays the foundation for map-based cloning and marker-assisted selection of Yr85.

In China, Xinjiang is a relatively independent epidemic region of wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, due to great population genetic divergence of Xinjiang with other inland epidemic regions. In this region, race evolution was usually slower than inland populations. However, many new races have recently been found, and therefore, it is necessary for more understanding of the virulence evolution of the Xinjiang population. So, in this study, a 65 sexual progenies, derived from a Xinjiang single-urediospore isolate BGTB-1 of P. striiformis f. sp. tritici by selfing on alternate host barberry (Berberis aggregata). It was phenotyped on the 25 single Yr lines, and genotyped by 19 kompetitive allele-specific PCR-single nucleotide polymorphism (KASP-SNP) markers. As a result, the 65 progenies were identified as 56 various virulence patterns (VPs), and neither of which was identical to the parental isolate, showed 100% virulence variation. Compared with the parental isolate, of all progenies, 39 (60.0%) had increased virulence, and 18 (27.7%) had decreased virulence. All progenies exhibited avirulence to Yr10, Yr15, Yr32, and YrTr1 loci, and avirulence and virulence segregation at the remaining 21 Yr resistance loci. The results showed avirulence to Yr5, Yr7, and Yr76 (A:V≈3:1) loci is controlled by a single dominant gene, and that to Yr6, Yr25, and Yr44 (A:V≈1:3) loci by a single recessive gene. However, avirulence to the remaining 15 resistant loci including Yr1, Yr2, Yr3, Yr4, Yr8, Yr9, Yr17, Yr26 (=Yr24), Yr28, Yr29, Yr43, YrSP, Yr27, YrA, and YrExp2, with various avirulence and virulence segregation ratios, is controlled by two genes with different gene effects, indicating complex genetic traits of the parental isolate. Totally, 65 dissimilar genotypes detected among progenies using overall molecular markers, by which a linkage map was constructed, with a genetic distance of 441.0 cM. Interestingly, although the parental isolate was avirulent to Yr5, but 17 progenies showed virulence, showing the change of pathogenicity from avirulence to virulence at this resistance locus. It was for the first time to report that progenies with virulence to Yr5 produced sexually from avirulent parental isolate at this resistance locus. To our knowledge, this study offers an insight into inheritance, sexual reproduction and virulence variation of P. striiformis f. sp. tritici in Xinjiang, facilitating us to understand evolution of the rust pathogen in this region and accounting for Xinjiang population distinguished form other inland populations. Additionally, it is necessary to further confirm the roles of sexual reproduction in the emergence of new races and affecting population genetic diversity of P. striiformis f. sp. tritici under natural conditions in Xinjiang.

Most modern wheat cultivars were selected on the basis of yield-related indices measured under optimal fertilizer and irrigation inputs. With climate change, land degradation and salinity caused by sea water encroachment, wheat is increasingly subjected to environmental stress. Moreover, expanding urbanization increasingly encroaches upon prime agricultural land in countries like China, and alternative cropping areas must be found. Some of these areas have moderate constraining factors, such as salinity. Therefore, it is important to investigate whether current genetic materials and breeding procedures are maintaining adequate variability to address future problems caused by abiotic stress. In this study, a panel of 307 wheat accessions, including local landraces, exotic cultivars used in Chinese breeding programs and Chinese cultivars released during different periods since 1940, were subjected to a genome-wide association study to dissect the genetic basis of salinity tolerance. Both marker-based and pedigree-based kinship analyses revealed that favorable haplotypes were introduced in some exotic cultivars as well as a limited number of Chinese landraces from the 1940s. However, improvements in salinity tolerance during modern breeding are not as obvious as that of yield. To broaden genetic diversity for increasing salt tolerance, there is a need to refocus attention on local landraces that have high degrees of salinity tolerance and carry rare favorable alleles that have not been exploited in breeding.

The objective of this review is to describe events in China and elsewhere that are related to the discovery, genetic identification, use, and ultimate break-down of a single wheat gene for resistance to stripe rust, namely Yr24/Yr26. In our retrospective analysis there was an early assumption of at least three genes at or near the locus, which caused an erroneous presumption of genetic diversity for resistance. It is an example of another boom and bust cycle in plant breeding with races virulent to Yr26 (V26 races) now being the majority race group in the Chinese Pst population. We have attempted to present our story in a historical and personal context demonstrating research inputs from different national and international groups, as well as some significant contemporary side issues. It covers the period from the late 1980s to 2017, during which significant rapid advances in the molecular biology of host: pathogen genetics occurred. We attempt to describe both successes and drawbacks in our work.