On the North China Plain, one of the most water-deficient regions in China, bare fallow has been implemented over a large-scale area to conserve water during the growth season of water-intensive winter wheat since 2015. However, the effects of this bare fallow on fungal community and the occurrence of crop diseases are poorly understood. Here we measured soil chemical properties, fungal community composition, and the occurrence of crop diseases after 15 years of long-term fallow (continuous maize or soybean) and non-fallow (maize-wheat rotation; soybean-wheat rotation) cropping systems. Bare fallow during the winter-wheat growth season significantly decreased soil organic matter, available nitrogen, and phosphorus. It also changed the composition of soil fungal communities, i.e., increased relative abundances of some potentially pathogenic species of Lectera, Fusarium, and Volutella but decreased beneficial Cladorrhium and Schizothecium. Meanwhile, the epidemic tendency of maize diseases changed correspondingly: the disease index of southern corn leaf blight and maize brown spot increased, but the incidence of stalk rot decreased compared with the non-fallow system. Soybean diseases were very mild regardless of the cropping system during the total experimental period. Network analysis demonstrated that the soil fungal diversity associated with maize diseases was affected by the decreased soil organic matter and available nitrogen and phosphorus. Our results suggest that bare fallow in the winter-wheat season affected the soil chemical properties, fungal community, and the occurrence of maize fungal diseases.

Bipolaris maydis partitivirus 36 (BmPV36) is a mycovirus that can significantly reduce the virulence of the host Bipolaris maydis, but its hypovirulence mechanism is not clear. To investigate the response of B. maydis to BmPV36, the effects of BmPV36 on host cell structure and gene expression were studied via transmission electron microscopy and transcriptome sequencing using BmPV36-carrying and virus-free mycelium on the second and fifth culture. The results of transmission electron microscopy showed that the cell wall microfibrils of B. maydis were shortened, the cell membrane was broken, and membrane-bound vesicles and vacuoles appeared in the cells after carrying BmPV36. Transcriptome sequencing results showed that after carrying BmPV36, B. maydis membrane-related genes were significantly up-regulated, but membrane transport-related genes were significantly down-regulated. Genes related to carbohydrate macromolecule polysaccharide metabolic and catabolic processes were significantly down-regulated, as were genes related to the synthesis of toxins and cell wall degrading enzymes. Therefore, we speculated that BmPV36 reduces the virulence of B. maydis by destroying the host’s cell structure, inhibiting the synthesis of toxins and cell wall degrading enzymes, and reducing cell metabolism. Gaining insights into the hypovirulence mechanism of mycoviruses will provide environmentally friendly strategies for the control of fungal diseases.

Wheat crown rot (WCR) is a significant soil-borne disease affecting wheat production worldwide. Understanding the impact of wheat crown rot on the structure and function of microbial communities in the wheat rhizosphere soil can provide a theoretical basis for the mining biological control resources against WCR. In this study, rhizosphere soils with varying WCR severities (light, moderate, severe) were analyzed for chemical properties, microbial community composition and functions using high-throughput sequencing. The results revealed that WCR decreased rhizosphere soil pH, the content of available nitrogen and phosphorus, and the abundance of beneficial taxa such as Bacillus and Streptomyces. Additionally, functional predictions showed that microbial communities adapted to WCR by enhancing signaling pathways and reducing their anabolic activity. From soil with light WCR occurrence, we isolated Bacillus velezensis BF-237, whose abundance was reduced by WCR. Greenhouse experiments demonstrated that BF-237 achieved a control efficiency of 56.61% against WCR in artificially inoculated sterilized soil and 53.32% in natural soil. This study clarifies the impact of wheat crown rot on the community structure, and function of rhizosphere soil microorganisms, alongside identifying a promising biocontrol agent. These findings contribute to understanding WCR pathogenesis and offer practical resources for its management.

Watermelon is one of the most important fruits in China, accounting for more than 70% of the world’s total output. Fusarium wilt of watermelon is the most common and serious disease in the cultivation of watermelon. It is mainly caused by Fusarium oxysporum f. sp. niveum (FoN), which has caused serious damage to the watermelon-planting industry. Some mycoviruses can reduce the pathogenicity of host pathogens and have the potential for biocontrol, so their application potential in the biological control of plant fungal diseases has attracted much attention. In this study, high-throughput sequencing was performed on 150 FoN strains isolated from three major watermelon-production areas (northern semi-arid area, northwestern arid area, and southern humid area) to detect the diversity of mycoviruses and to uncover new mycoviruses. The analysis identified 25 partial or complete genome segments representing eight previously undescribed mycoviruses. The existence of six mycoviruses was verified via RT-PCR. The southern humid area had the highest diversity of mycoviruses, with 15 species identified. Among these, 40% are dsRNA viruses and 33.3% belong to the family Chrysoviridae, representing the predominant viral type and family. In the northern semi-arid area, a total of 12 viral species were identified, among these 41.7% were +ssRNA viruses and 25% belonged to the family Mymonaviridae, constituting the main viral types and family. The northwestern arid area showed relatively low viral diversity, only containing three species. Two of these were +ssRNA viruses classified under the Mitoviridae and Potyviridae families. Notably, only one virus, Fusarium oxysporum f. sp. niveum Potyvirus 1 (FoNPTV1), was shared across all three areas. These findings reveal significant regional differences in the mycoviral species composition and distribution, highlighting the complex interactions between mycoviruses and FoN in different environments. By uncovering new mycoviruses associated with FoN, this study provides valuable resources for the potential biocontrol of Fusarium wilt in watermelon, contributing to sustainable disease management and improving the quality and safety of watermelon production in China.

Fusarium crown rot, a widespread and destructive disease affecting cereal crops (particularly wheat and barley), is primarily caused by the soil-borne fungal pathogen Fusarium pseudograminearum. Secondary metabolites (SMs) play a crucial role in colonization and host tissue invasion by pathogenic fungi. In this study, we investigated the functional role of FpTox2, a secondary metabolite-related gene in F. pseudograminearum. An FpTox2 deletion mutant exhibited significantly reduced radial growth compared to wild-type F. pseudograminearum. Notably, the mutant strain completely lost conidiation capacity under induced conditions. Furthermore, although it showed decreased sensitivity to the cell membrane inhibitor sodium dodecyl sulfate (SDS), the mutant demonstrated enhanced susceptibility to NaCl, a metal ion stressor. Most importantly, the pathogen’s virulence was markedly attenuated in wheat stem base infections following FpTox2 deletion, and we demonstrated that FpTox2 regulates pathogen virulence by influencing deoxynivalenol production. In conclusion, FpTox2 is crucial for vegetative growth, asexual development, abiotic stress responses, and full virulence in F. pseudograminearum.

Soil salinization threatens global agricultural sustainability and may elevate soil-borne disease risk through coordinated changes in soil conditions and the rhizosphere microbiome, yet long-term field evidence remains limited. Here, a 19-year controlled field experiment with an artificial salinity gradient (non-saline, moderate, and severe) was conducted to characterise salinity-associated responses of soil physicochemical properties, wheat crown rot (WCR), and the rhizosphere microbiome. A 3-year field remediation demonstration was implemented to test whether replacing saline irrigation with non-saline water could reverse soil deterioration and reduce disease severity. The results showed that severe salinity increased soil pH from 7.64 to 8.38 and reduced available phosphorus, total nitrogen, and available potassium by 54.11%, 14.63%, and 37.69%, respectively, while the WCR disease index increased from 10.51 to 32.88. It also reduced microbial richness and diversity, altered rhizosphere community composition, with taxon-specific abundance shifts among halophilic taxa, and redistributed community functional potential, with greater representation of genes associated with compatible-solute metabolism and ion homeostasis alongside changes in carbon, nitrogen, and sulfur metabolism. Remediation reduced soil salinity and pH, improved nutrient availability, and decreased the WCR disease index by 49.17%. Together, our results show that long-term salinization is associated with coordinated deterioration of soil conditions, restructuring of the rhizosphere microbiome, redistribution of microbial functional potential, and increased WCR severity. The remediation experiment showed that reducing salinity improved soil conditions and reduced disease severity. Re-establishing favourable soil abiotic conditions may be a prerequisite for alleviating disease risk in salinized agroecosystems.