Endophytic bacteria from diseased plant leaves as potential biocontrol agents of cucumber Fusarium wilt

Cucumber Fusarium wilt caused by Fusarium oxysporum is a serious soil-borne disease, which seriously affects the yield of cucumber. When plant roots are subjected to invasion by pathogenic bacteria, endophytic microbial communities also change greatly. Screening for Fusarium wilt antagonistic bacteria has generally focused on screening for antagonistic strains from healthy plants, with few reports of screening for antagonists from leaves of diseased plants. In this study, the leaves of cucumber plants infected with Fusarium wilt disease were used for the isolation of antagonists and a total of four endophytes with obvious antagonistic effects were screened. 16S rDNA gene sequencing confirmed that the four strains belonged to Paenibacillus polymyxa (Y-4, Y-6, Y-14) and Bacillus zanthoxyli (Y-9), and that all antagonistic strains exhibited the ability to produce amylase, pectinase and hydrogen peroxide (H₂O₂). In the pot experiment, four antagonistic strains all could significantly reduce the disease index of cucumber Fusarium wilt caused by Fusarium oxysporum f. sp. cucumerinum Owen (FOC) and promote root growth. Furthermore, the cucumber plants with antagonistic bacteria treatment possessed higher photosynthetic pigment content, antioxidant capacity, proline content and root vigor. These results indicated the leaves of cucumber diseased strain may also be a potential source for screening novel antagonistic agents against cucumber Fusarium wilt.