Streptomyces alfalfae XN-04 has been reported for the production of antifungal metabolites effectively to control Fusarium wilt of cotton, caused by Fusarium oxysporum f. sp. vasinfectum (Fov). In this study, we used integrated statistical experimental design methods to investigate the optimized liquid fermentation medium components of XN-04, which can significantly increase the antifungal activity and biomass of XN-04. Seven variables, including soluble starch, KNO₃, soybean cake powder, K₂HPO₄, MgSO₄·7H₂O, CaCO₃ and FeSO₄·7H₂O, were identified as the best ingredients based on one-factor-at-a-time (OFAT) method. The results of Plackett–Burman Design (PBD) showed that soluble starch, soybean cake powder and K₂HPO₄ were the most significant variables among the seven variables. The steepest climbing experiment and response surface methodology (RSM) were performed to determine the interactions among these three variables and fine-tune the concentrations. The optimal compositions of medium were as follows: soluble starch (26.26 g/L), KNO₃ (1.00 g/L), soybean cake powder (23.54 g/L), K₂HPO₄ (0.27 g/L), MgSO₄·7H₂O (0.50 g/L), CaCO₃ (1.00 g/L) and FeSO₄·7H₂O (0.10 g/L). A verification experiment was then carried out under the optimized conditions, and the results revealed the mycelial dry weight of S. alfalfae XN-04 reaching 6.61 g/L. Compared with the initial medium, a 7.47-fold increase in the biomass was achieved using the optimized medium. Moreover, the active ingredient was purified from the methanol extract of S. alfalfae XN-04 mycelium and then identified as roflamycoin (a polyene macrolide antibiotic). The results may provide new insights into the development of S. alfalfae XN-04 fermentation process and the control of the Fusarium wilt of cotton and other plant diseases.

Fusarium head blight (FHB) of wheat, predominately caused by Fusarium graminearum, is an economically important plant disease worldwide. With increased fungicide resistance, controlling this filamentous fungal disease has become an enormous challenge. Biocontrol agents alone or integrated with other methods could better manage FHB. Streptomyces pratensis S10 has strong antagonistic activity against FHB as reported in our previous study. We now have investigated S10 controls of FHB in more detail by combining microscope observations, biological assays, and transcriptome profiling. S10 culture filtrates (SCF) significantly inhibited essential stages of the life cycle of F. graminearum in the laboratory and under simulated natural conditions. SCF at different concentrations inhibited conidiation of F. graminearum with an inhibition of 57.49 to 83.83% in the medium and 64.04 to 85.89% in plants. Different concentrations of SCF reduced conidia germination by 47.33 to 67.67%. Two percent (vol/vol) SCF suppressed perithecia formation of F. graminearum by 84 and 81% in the laboratory and under simulated natural conditions, respectively. The S10 also reduced the pathogenicity and penetration ability of F. graminearum by suppressing ATP production. Collectively, these findings indicate that S. pratensis S10 should be explored further for efficacy at controlling FHB.

Fusarium graminearum, a devastating fungal pathogen, causes great economic losses to crop yields worldwide. The present study investigated the potential of Streptomyces pratensis S10 to alleviate F. graminearum stress in wheat seedlings based on plant growth-promoting and resistance-inducing assays. The bioassays revealed that S10 exhibited multiple plant growth-promoting properties, including the production of siderophores, 1-aminocyclopropane-1-carboxylic acid deaminase (ACC), and indole-3-acetic acid (IAA), phosphate solubilization, and nitrogen fixation. Meanwhile, the pot experiment demonstrated that S10 improved wheat plant development, substantially enhancing wheat height, weight, root activity, and chlorophyll content. Consistently, genome mining identified abundant genes associated with plant growth promotion. S10 induced resistance against F. graminearum in wheat seedlings. The disease incidence and disease index reduced by nearly 52% and 65% in S10 pretreated wheat seedlings, respectively, compared with those infected with F. graminearum only in the non-contact inoculation assay. Moreover, S10 enhanced callose deposition and reactive oxygen species (ROS) accumulation and induced the activities of CAT, SOD, POD, PAL, and PPO. Furthermore, the quantitative real-time PCR (qRT-PCR) results indicated that S10 pretreatment increased the expression of SA- (PR1.1, PR2, PR5, and PAL1) and JA/ET-related genes (PR3, PR4a, PR9, and PDF1.2) in wheat seedlings upon F. graminearum infection. In summary, S. pratensis S10 could be an integrated biological agent and biofertilizer in wheat seedling blight management and plant productivity enhancement.

Fusarium head blight (FHB) of wheat, mainly caused by Fusarium graminearum, leads to severe economic losses worldwide. Effective management measures for controlling FHB are not available due to a lack of resistant cultivars. Currently, the utilization of biological control is a promising approach that can be used to help manage FHB. Previous studies have confirmed that Streptomyces pratensis S10 harbors excellent inhibitory effects on F. graminearum. However, there is no information regarding whether invasive hyphae of F. graminearum are inhibited by S10. Thus, we investigated the effects of S10 on F. graminearum strain PH-1 hypha extension, toxisome formation, and TRI5 gene expression on wheat plants via microscopic observation. The results showed that S10 effectively inhibited the spread of F. graminearum hyphae along the rachis, restricting the infection of neighboring florets via the phloem. In the presence of S10, the hyphal growth is impeded by the formation of dense cell wall thickenings in the rachis internode surrounding the F. graminearum infection site, avoiding cell plasmolysis and collapse. We further demonstrated that S10 largely prevented cell-to-cell invasion of fungal hyphae inside wheat coleoptiles using a constitutively green fluorescence protein-expressing F. graminearum strain, PH-1. Importantly, S. pratensis S10 inhibited toxisome formation and TRI5 gene expression in wheat plants during infection. Collectively, these findings indicate that S. pratensis S10 prevents the spread of F. graminearum invasive hyphae via the rachis.