The present work was conducted to screen and identify biocontrol bacteria that effectively reduce the severity of corn stalk rot (CSR) and clarify the antifungal activity of secondary metabolites. The bacterial strain (BM21) was isolated from corn rhizosphere soil that effectively reduced CSR in pot experiments. On the basis of phylogenetic reconstructions, 16S rRNA sequence analysis, and biochemical and physiological reactions, BM21 was identified as Bacillus velezensis. The strain exhibited remarkable antifungal activity against Fusarium graminearum, a pathogenic fungus that causes CSR. Extracellular antifungal substances (10%) isolated from BM21 inhibited F. graminearum mycelial growth by 79.2%, conidial germination by 84.0%, and conidial production by 78.1%. In addition, the extracellular antifungal substances caused mycelial malformation and ultra-structural changes. The extracellular antifungal substances were sensitive to heat and showed a degree of resistance to ultraviolet radiation. The optimum pH for antifungal activity was 6–8. In pot experiments, irrigation with aqueous extracts from BM21 (1.0 mL/plant) reduced CSR incidence by 72.4–77.4%. B. velezensis BM21 effectively reduced CSR incidence and showed a potential as a biocontrol agent to control CSR.

Introduction: Soybean root rot (SRR), caused byFusarium oxysporum, is a severe soil-borne disease in soybean production worldwide, which adversely impacts the yield and quality of soybean. The most effective method for managing crop soil-borne diseases and decreasing reliance on chemical fungicides, such asBacillusspp., is via microbial biocontrol agents.Methods and Results: In this study, a soil-isolated strain BVE7 was identified asB. velezensis, exhibiting broad-spectrum activity against various pathogens causing soybean root rot. BVE7 sterile filtrate, at a concentration of 10%, demonstrated significant antifungal activity by inhibiting the conidial germination, production, and mycelial growth ofF. oxysporumby 61.11%, 73.44%, and 85.42%, respectively, causing hyphal malformations. The antifungal compound produced by BVE7 demonstrated adaptability to a standard environment. The pot experiment showed that BVE7 suspension could effectively control soybean root rot, with the highest control efficiency of 75.13%. Furthermore, it considerably enhanced the activity of catalase, phenylalanine ammonia lyase, superoxide dismutase, and peroxidase in soybean roots, while also preventing an increase in malondialdehyde activity. By improving the host resistance towards pathogens, the damage caused by fungi and the severity of soybean root rot have been reduced.Discussion: This study presents the innovative utilization ofB. velezensis, isolated from soybean roots in cold conditions, for effectively controlling soybean root rot caused byF. oxysporum. The findings highlight the remarkable regional and adaptive characteristics of this strain, making it an excellent candidate for combating soybean root rot in diverse environments. In conclusion,B. velezensisBVE7 demonstrated potential in effectively reducing SRR incidence and can be considered as a viable option for SRR management.

Alfalfa long-term continuous cropping (CC) can pose a serious threat to alfalfa production. However, the mechanism of alfalfa CC obstacle is unclear as of today. Our preliminary study showed that the main factors of CC obstacle were not the lack of nutrients or water in alfalfa rhizosphere soils. Further, we evaluated physic-chemical property, microbial population structure, and metabolite differences of alfalfa rhizosphere soils with CC for 1, 7, and 14 years based on analysis of metabolomics and microbiomics. Four phenolic acid metabolites, including p-coumaric acid, ferulic acid, vanillic acid, and p-hydroxybenzoic acid, were found to have significant differences among different CC years, which may be the key factors of CC obstacle. Among them, p-coumaric acid and ferulic acid could significantly decrease the germination rate of alfalfa seeds by 21.11 and 16.67% at the concentration of 100 μg/mL and the height (root length) of alfalfa seedlings by 21% (32.9%) and 13.72% (16.45%). Moreover, these metabolites could effectively promote the growth of some pathogenic fungi, causing alfalfa root rot. Among them, p-coumaric acid obviously and significantly aggravated the occurrence of alfalfa root rot. With the increase of CC years, soil microbial community changed from fungi to bacteria; fungi decreased by 10.83%, fungi increased by 8.08%, and beneficial microorganisms decreased with the increase of CC years. Field analysis and experimental verification showed that the above results were consistent with that of CC obstacle in the field. Among the key metabolites, the autotoxicity of p-coumaric acid was the strongest. This study fully proved that the continuous accumulation of autotoxic substances in alfalfa rhizosphere was the key factor causing alfalfa CC obstacles.

Carrot (Daucus carota L.), which is one of the 10 most important vegetable crops worldwide, is an edible root vegetable desired for its taste as well as its medicinal uses. However, a fungus isolated from carrot seeds was observed to substantially decrease the germination rate. The isolate was identified as Alternaria alternata based on morphological and molecular characteristics as well as a phylogenetic tree. The maximum seed infection rate of selected carrot cultivars was approximately 60%, with the main infection site just underneath the seed shell. Additionally, the germination rate of infected seeds decreased by 28.7%. However, the seed infection rate varied among the examined carrot cultivars. Regarding the effects of chemical fungicides, the optimal treatment involved immersing seeds in amistar top suspension concentrate (SC) (effective concentration of 0.65 g/L) for 6 h, which effectively killed the fungi inside the carrot seeds. The results of this study provide a theoretical basis for the development of efficient methods for preventing the infection of carrot seeds by specific fungi and increasing the germination rate and vigour index.

Corn stalk rot, caused by Fusarium graminearum, is one of the most destructive diseases of maize in many regions of the world. A bacterial strain BV23 was isolated from corn rhizosphere that reduced corn stalk rot significantly in greenhouse studies in 2016 and 2017. BV23 was identified as Bacillus vallismortis, which showed antagonistic effects against a number of fungal pathogens, including F. graminearum, Rhizoctonia solani, Athelia rolfsii, and Thanatephorus cucumeris. BV23 had the greatest fungistatic effect on F. graminearum, inhibiting mycelial growth by 66.2%, conidial germination by 90.1%, and conidial production by 86.7%. The probable antifungal mechanism was assessed by examining the morphology and ultrastructure of F. graminearum hyphae. Treatment by BV23 culture supernatant resulted in coarser hyphae, induced cytoplasmic granulation, and increased cell membrane permeability of F. graminearum, causing cytoplasm leakage. These effects became increasingly obvious with increasing concentration (1%, 5% and 10%). Furthermore, the antifungal active substances were sensitive to heat.