Abstract
Continuous monoculture of cucumber (Cucumis sativus L.) typically leads to the frequent incidence of Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum (FOC). As potent allelochemicals, phenolic acids are believed to be associated with soilborne diseases. This study aimed to investigate the effect of single or co-inoculation of antagonistic bacteria Bacillus amyloliquefaciens B2 and phenolic acid-degrading fungus Pleurotus ostreatus P5 on the suppression of cucumber Fusarium wilt. The strain B2 was identified as B. amyloliquefaciens based on biochemical, physiological, and 16S rDNA and gyrB gene sequence analyses. Strain B2 showed indole-3-acetic acid (IAA) and siderophore production and phosphate solubilization in in vitro assays. Scanning electron microscope (SEM) imaging showed the ability of strain B2 to adhere to the root surface of cucumber. P. ostreatus P5 could effectively degrade mixed phenolic acids as its sole source of carbon and energy for growth in liquid medium. In a pot experiment, four treatments were established as follows: (1) CK, uninoculated control; (2) B2, inoculation of strain B2; (3) P5, inoculation of strain P5; and (4) B2 + P5, co-inoculation of strain B2 and strain P5. At the end of the 60-day pot experiment, the B2, P5, and B2 + P5 treatments significantly reduced disease incidence by 48.1, 22.2, and 63.0%, respectively, compared to the CK treatment (p < 0.05). All three inoculation treatments significantly increased the growth of cucumber seedlings and suppressed the FOC population compared to the control (p < 0.05). High-performance liquid chromatography (HPLC) analysis showed that total phenolic acids were decreased by 18.9, 35.9, and 63.2% in the B2, P5, and B2 + P5 treatments, respectively. The results from this study suggest that combined application of B. amyloliquefaciens B2 and P. ostreatus P5 could be a promising strategy for suppressing Fusarium wilt and improving plant growth of cucumber seedlings under continuous cropping conditions.
Highlights
Cucumber (Cucumis sativus L.) is an economically important vegetable crop worldwide, and Fusarium wilt of cucumber caused by Fusarium oxysporum f. sp. cucumerinum (FOC) has become the major limiting factor in the cucumber continuous cropping system (Ye et al, 2006; Raza et al, 2017)
The phylogenetic analysis of 16S rDNA sequences clearly showed that the strain B2 and B. amyloliquefaciens were clustered together (Figure 3A)
Based on physiological and biochemical testing, and 16S rDNA and gyrB gene sequences analyses, strain B2 was identified as B. amyloliquefaciens
Summary
Cucumber (Cucumis sativus L.) is an economically important vegetable crop worldwide, and Fusarium wilt of cucumber caused by Fusarium oxysporum f. sp. cucumerinum (FOC) has become the major limiting factor in the cucumber continuous cropping system (Ye et al, 2006; Raza et al, 2017). Cucumber (Cucumis sativus L.) is an economically important vegetable crop worldwide, and Fusarium wilt of cucumber caused by Fusarium oxysporum f. Traditional control strategies, including the use of fungicide, rotation, and resistant cultivar, have been suggested to control cucumber Fusarium wilt; these approaches are not environmentally friendly, economical, or reliable (Cao et al, 2011; Raza et al, 2017; Han et al, 2019). Biological control represents an attractive alternative method for protection of crops against Fusarium wilt. Many microbial species such as Bacillus spp., Pseudomonas spp., Trichoderma spp., Streptomyces spp., and Acinetobacter spp. have been shown to effectively control FOC (Raza et al, 2017; Kumar et al, 2020; Netzker et al, 2020). The primary mechanism probably involves secreting antimicrobial compounds, competing for biological niche and nutrients, and inducing plant resistance (Shafi et al, 2017; Netzker et al, 2020)
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