Green manures of Indian mustard and wild rocket enhance cucumber resistance to Fusarium wilt through modulating rhizosphere bacterial community composition

Abstract

Green manuring can suppress crop diseases and change soil microbial communities, but the functional significances of changes in soil microbial communities are unclear. Effects of Indian mustard (Brassica juncea), wild rocket (Diplotaxis tenuifolia) and wheat (Triticum aestivum) green manures on cucumber (Cucumis sativus L.) Fusarium wilt disease caused by Fusarium oxysporum f.sp. cucumerinum (FOC) were evaluated. Cucumber rhizosphere microbial communities were analyzed by real-time PCR and high-throughput amplicon sequencing. Furthermore, feedback effects of rhizosphere biota on cucumber resistance to FOC were assessed. All green manures promoted cucumber growth and changed rhizosphere bacterial community composition. Indian mustard and wild rocket green manures decreased Fusarium wilt disease severity and rhizosphere FOC abundance, increased bacterial diversity and abundance of potential plant-beneficial microorganisms. Rhizosphere biota from cucumber cultivated with Indian mustard and wild rocket (but not with wheat) green manures suppressed Fusarium wilt disease and enhanced expression of defense-related genes in cucumber seedling roots. Pseudomonas spp. strains isolated from cucumber rhizosphere cultivated with Indian mustard and wild rocket green manures suppressed cucumber Fusarium wilt disease. Changes in cucumber rhizosphere microbial communities induced by Indian mustard and wild rocket suppressed Fusarium wilt disease by priming for defense in plants.