Fusarium oxysporum, a primary soil-borne fungus that affects rice seedlings globally, is responsible for rice seedling blight (RSB), which reduces seedling quality and survival rates. The synthetic fungicides used to treat this disease negatively affect human health and the environment. A biocontrol bacterial isolate, Bacillus velezensis Bv S3, isolated from the rice rhizosphere, showed a strong antagonistic effect on RSB-causing F. oxysporum. The ratio of the longest to the shortest radius of F. oxysporum following Bv S3 inoculation was 2.52 (cm/cm) in a plate standoff experiment. This was different from the other biocontrol strains. Bv S3 exhibits a wide spectrum of antifungal activity against various pathogenic fungi that cause RSB. When 10% Bv S3 liquid culture filtrate was applied, it dramatically reduced F. oxysporum spore germination and mycelial growth, with inhibition rates of 66.7%, and 45.7%, respectively, and caused hyphal malformations. Furthermore, the Bv S3 suspension (1 × 10⁸ CFU/mL) reduced RSB by 65.5% and 76.5% in pot experiments, effectively promoted the growth of rice seedlings, and improved the activities of neutral phosphatase, urease, invertase, and catalase in rice rhizosphere soil. The active substances produced by Bv S3 were sensitive to temperature and ultraviolet irradiation, and the antifungal effect significantly increased after 90 min of exposure, with antifungal effect observed at pH 7. Bv. S3 effectively reduced the incidence of RSB and showed potential as a biocontrol agent.

Soybean root rot, a soil-borne fungal disease, is caused by multiple pathogens that seriously affect soybean production. During spring 2021, 92 pathogenic fungal strains were isolated from soybean plants with root rot in Hailun City, Heilongjiang Province, China. Through morphological and molecular identification, these strains were identified as Fusarium oxysporum (39.1%), F. asiaticum (30.4%), F. graminearum (13.0%), Pythium macrosporum (8.7%), and Rhizoctonia solani (8.7%). Among them, F. oxysporum was the dominant species, and F. asiaticum, not previously reported as a soybean root rot pathogen in Northeast China. Approximately 50% of the F. asiaticum isolates were moderately pathogenic. In addition, F. asiaticum had a wide host range, infecting black soybean, French bean, white hyacinth bean, mung bean, and adzuki bean but not corn, peanut, rice, and oat roots. Regarding field management, fludioxonil and pyraclostrobin had the best control effects of 73.8% and 69.4%, with EC₅₀ values of 0.0029–0.0071 μg·mL⁻¹ and 0.0045–0.0076 μg·mL⁻¹, respectively. The study reported that F. asiaticum is a pathogen causing soybean root rot in northeast China. The application of chemical fungicides and non-host crop rotation can effectively control the disease caused by F. asiaticum.

Rice seedling blight is a globally occurring seedling disease caused by multiple pathogens. It is currently the most common disease affecting rice production in northeast China; hence, determining the causal agents, including its biological characteristics, host range, and fungicide efficacy is vital for its effective management. The present study obtained 45 pathogenic isolates from diseased rice seedlings in Suihua, Heilongjiang Province, China. Of these, five pathogens were identified based on their morphology and molecular identification, while 10 oomycete isolates were identified as Pythium aristosporum—the first to be reported in rice seedling blight. Its optimum growth conditions include a temperature of 25 °C, pH 6, and photoperiod of 24 h. Except for soybean (Glycine max (L.) Merr.), black soybean (Glycine max var.), and cucumber (Cucumis sativus L.), P. aristosporum can potentially infect and cause seedling blight on other hosts, such as wheat (Triticum aestivum L.), maize (Zea mays L.), sorghum (Sorghum bicolor (L.) Moench), alfalfa (Medicago sativa L.), oats (Avena sativa L.), and white clover (Trifolium repens L.). Its isolates were found to be highly sensitive to metalaxyl + propamocarb (EC₅₀ = 0.0138 μg/mL) with 84.1% efficacy at 313 μg/mL. These results can serve as the basis for controlling P. aristosporum.

Soybean root rot caused by Rhizoctonia solani is a yield-limiting disease in Northeast China, particularly under continuous monoculture and cool climatic conditions. Despite its agronomic impact, the epidemiology and fungicide resistance profile of the pathogen remain inadequately characterized. In this study, a comprehensive survey conducted in Heilongjiang Province yielded 990 pathogenic isolates belonging to 11 fungal species. Among them, 55 strains were identified as R. solani based on combined morphological and molecular analyses. These isolates induced typical symptoms of root and stem browning with constriction. Pathogenicity tests on 30 R. solani isolates indicated that 83.3% were highly pathogenic. The pathogen exhibited a distinct geographic distribution, with the highest percentage of pathogen isolation recorded in Jiamusi (26.6%), which accounted for 61.8% of all R. solani isolates. In vitro fungicide sensitivity assays demonstrated that fludioxonil and prochloraz were highly effective (EC₅₀ < 0.0050 µg·mL⁻¹), whereas resistance was observed to tebuconazole, difenoconazole, pyraclostrobin, and carbendazim. Pot experiments confirmed that fludioxonil seed treatment (15 g a.i./100 kg seeds) provided superior control efficacy (63.07%) compared to prochloraz (46.85%). These findings establish R. solani as a dominant causal agent of soybean root rot in the region and support the prioritized use of fludioxonil for sustainable disease management. By elucidating the pathogenicity, distribution, and resistance patterns of R. solani, this study provides critical insights for controlling soybean root rot in cold-climate production systems and facilitates the development of targeted management strategies.

Adzuki bean (Vigna angularis [Willd.] Ohwi & H. Ohashi) is a high-value legume crop widely cultivated globally, primarily in Asia, for its nutritional benefits and economic importance. In 2023, an epidemic outbreak of stem rot disease was observed in commercial adzuki bean fields in Shangzhi City, Heilongjiang Province, China. Through tissue isolation and fulfillment of Koch’s postulates, nine pathogenic fungal isolates were obtained from diseased stems. Morphological, molecular, and phylogenetic analyses identified Fusarium graminearum Schwabe and F. oxysporum f. sp. glycines as the causal agents, representing the first report of these fungi causing stem rot on adzuki bean in China. Pathogenicity testing of nine plant species (seven legumes and two cereals: corn and wheat) revealed that all tested crops commonly cultivated in Northeast China were susceptible to infection by F. graminearum and F. oxysporum. In vitro screening identified high sensitivity of F. graminearum to tebuconazole, with 80.0% mycelial growth inhibition at 4.3 × 10 ⁻⁴ g·ml ⁻¹ , and high sensitivity of F. oxysporum to ethylicin, with 82.7% inhibition at 8.0 × 10 ⁻⁴ g·ml ⁻¹ . This study provides a comprehensive characterization of the pathogens, defines their host range, and identifies tebuconazole and ethylicin as effective candidates for field control, offering management strategies to protect adzuki bean production in Heilongjiang Province.

Soybean root rot, a destructive soilborne disease complex caused by a consortium of pathogenic fungi, poses a persistent threat to global soybean productivity. During 2022–2023, a total of 990 fungal isolates were recovered from symptomatic soybean roots across Heilongjiang Province, Northeast China. Of these, 279 isolates were identified as Fusarium equiseti through integrated morphological characterization and multilocus phylogenetic analysis. Notably, F. equiseti exhibited markedly elevated isolation frequencies (5.6–58.9%) across surveyed regions, confirming its status as the emerging dominant causal agent of root rot in this agroecological zone. Pathogenicity evaluations revealed that 76.67% of isolates displayed moderate virulence, with one strain classified as highly virulent (3.33%). In vitro fungicide sensitivity assays indicated that F. equiseti was most susceptible to prochloraz (mean EC₅₀ = 0.0010 µg·mL⁻¹) and fludioxonil (mean EC₅₀ = 0.0042 µg·mL⁻¹). When deployed as seed treatments, these two fungicides achieved 53.61% and 47.32% control efficacy against root rot, respectively, while significantly enhancing soybean seedling emergence, root length, and fresh weight. Collectively, these findings provide a scientific foundation for the precise, sustainable management of F. equiseti-mediated root rot in cold-region soybean production systems.