Influence Of Cucumber Monoculture And Bacillus On The Fusarium Oxsporum-Feeding Bacteria

Cucumber wilt disease,caused by Fusarium oxysporum f.sp.cucumerinum(Foc),is one of the most important diseases in vegetable production in greenhouse.Mycosphere is a micro-habitat similar to rhizoshere,and the microorganisms in this habitat played important biological and ecological roles.Mycosphere bacteria colonized in pathogenic fungi may involve in the disease occurrence.This study will disclose the ecological relationship among Foc,Foc feeding bacteria and wilt disease under the monoculture condition and challenged with Foc inoculation.The influence of Bcillus sp.B006 on the colonization of Foc-feeding bacteria on Foc hyphae will be examined to provide more information for better application of Bcillus agents.Analysis of Foc-feeding bacterial coummunity under the condition of monoculture and Foc invasion by using Illumia high-throughput sequencing showed that cucumber monoculture and five generations monoculture after Foc invasion significantly shifted the Foc feeding bacterial comunity.The relative abundance of dominant genus Rhizobium sp.,Achromobacter sp.and Stenotrophomonas sp.changed significantly.In monoculture soil,the cultural Foc-feeding bacterial community structure showed a similar trend with uncultural bacterial community,while Foc invasion not only changed the relative abundance of Rhizobium sp.and Stenotrophomonas sp.,but also the bacteria Microbacterium sp.and Pseudoxanthomonas sp..Monoculture after Foc invasion still changed the relative abundance of Flavobacterium sp..Research on the functions of single Foc-feeding bacteria showed that 12 of 25 Foc-feeding bacterial isolates inhibited the Foc hyphae growth.Among them,the dominant bacteria genera Rhizobium spp.and Achromobacter spp.showed high inhibitive activity.Control efficacy test in greenhouse showed that different bacteria have different influence on disease occurrence.Thirteen of 15 isolates could suppress the disease development.Rhizobium sp.had the best control efficacy of 74% and62%,respectively,whether co-inoculated with middle-level virulent Foc strain or low virulent Foc strain.Pseudomonas putida showed inhibitive or promotive effect when it was co-inoculated with middle virulent Foc strain or low virulent Foc strain.However,strain Massilia sp.can promote the wilt disease with the increase of disease index at 31.1%(middle virulent strain)and 58.3%(low virulent strain)respectively;Olivibacter sp.promoted the disease development after co-inoculating with low virulent Foc strain.According to the relative abundance of dominant bacteria in high-throughput sequence analysis results,the bacteria complex was designed and the results of their efficacy in suppressing disease indicated that the variation of the proportion of dominant bacteria genera Rhizobium sp.and Achromobacter sp.didn’t affect their suppression on the disease severity,while the variation of the proportion of Rhizobium sp.,Stenotrophomonas sp.and Achromobacter sp.could significantly affect the cucumber growth.The microscopic obseration of some bacteria on Foc hyphae showed that Achromobacter sp.,Stenotrophomonas sp.,Olivibacter sp.and Massilia sp.could colonize on Foc hyphae and migrate along with the Foc hyphae growth.Bcillus sp.B006 could inhibit deleterious bacteria Massilia sp.andOlivibacter sp.growth,and its precense could reduce the population of Massilia sp.and Olivibacter sp.colonized on Foc hyphae after the cell suspension of strain B006 was co-cultured with Foc hyphae and the deleterious bacteria.This is the first study on the Foc-feeding bacterial community and its fuction under the conditions of monoculture and Foc invasion.The results indicated that monoculture and Foc invasion were main factors to influenc the Foc-feeding bacterial community and its function.The proportional change of dominant Foc-feeding bacteria could effect plant growth significantly and some of them could promote the disease severity.Introduce of Bcillus could reduce the number of deleterious bacteria colonized on Foc hyphae.In conclusion,the above results gave a new insight to the mechanisms of disease occurrence and outbreak and provide new clue for the control of soil borne disease.