Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive fungal diseases of wheat, and seriously threatens safe production of the crop worldwide.  In China, new races historically appeared and rapidly developed to be predominant races and have resulted in ineffectiveness and replacement of wheat resistance cultivars as well as massive reduction in yield.  In the present study, the relative parasitic fitness of the two newly-emerged Yr5-virulent races (TSA-6 and TSA-9) were compared with those of four currently predominant Chinese races (CYR31, CYR32, CYR33, and CYR34) based on evaluation on 10 Chinese wheat cultivars.  As a result, there were significant differences in the relative parasitic fitness parameters among overall tested races based on multiple comparison (LSD) analysis (P<0.05).  The principal component analysis (PCA) of overall parasitic fitness parameters indicated that the sporulation ability, infection and spore survivability, expansion capacity, and potential pathogenicity were the most important parasitic fitness attributes of the tested races.  Based on the establishment of extracted three principal components and a comprehensive factor score mathematical models, evaluations of the parasitic fitness attributes of tested races showed that the level of relative parasitic fitness of the tested six races was: CYR32 (1.15)>TSA-9 (0.95)>TSA-6 (0.92)>CYR34 (0.29)>CYR31 (–1.54)>CYR33 (–1.77).  The results indicated that two Yr5-virulent races TSA-9 and TSA-6 possessed relative parasitic fitness higher than races CYR34, CYR31, and CYR33, but lower than race CYR32, and have potential risks in developing to be predominant races.  Therefore, continual monitoring of both Yr5-virulent races, and their variants is needed.  The use of wheat cultivars (lines) with Yr5 resistance gene singly in wheat breeding is essential for being avoided, and is suggested to combine with other effective stripe rust resistance genes.

Globally recurrent extreme high temperature (HT) events severely limit rice production.  This study investigated whether a controlled moderate soil drying (MD) could replace the conventional well-watered (WW) regime to more effectively mitigate HT stress on pistil fertilization in photo-thermosensitive genetic male-sterile (PTGMS) rice, and examined the role of brassinosteroids (BRs).  Two PTGMS rice varieties were cultivated under normal temperature (NT) and HT conditions, paired WW and MD strategies during anthesis.  In conventional WW regime, waterlogging reduces BRs levels in roots and pistils due to excessive decomposition, weakening active water uptake driven by root activity and failing to alleviate transpiration-pulled passive water extraction hampered by restricted stomatal openings.  Thereby, it causes water imbalance in plants and weakened pistil function due to a suppressed ascorbate-glutathione (AsA-GSH) cycle and hyperactive nicotinamide adenine dinucleotide phosphate oxidase (NOX) activity.  This exacerbates pistil fertilization impairment and hybrid seed yield loss under HT stress.  Conversely, by promoting BR synthesis and inhibiting its decomposition in roots and pistils, the MD strategy enhanced root activity and transpiration-driven water uptake.  It maintained plant water balance and supported pistil function through suppressed NOX activity and an enhanced AsA-GSH cycle-driven redox homeostasis.  Thus, it mitigated HT-induced pistil fertilization impairment and hybrid seed yield loss.  The precise function of BRs in moderating the protective effects of MD against the detrimental impacts of HT stress on pistil fertilization in PTGMS rice was confirmed through genetic and chemical approaches.  Consequently, a controlled MD method proved to be more effective than the conventional WW regime in alleviating HT stress on pistil fertilization in PTGMS rice by promoting BR enhancement.

In China, Xinjiang is a relatively independent epidemic region of wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, due to great 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 there needs to be 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.