Combined Control On Fusarium Wilt Of Banana By Rotation Together With Application Of Bio-organic Fertilizer And Its Action Mechanism

Banana production has been severely hindered by the long-term practice of monoculture agriculture.Fusarium wilt disease,caused by the Fusarium oxysporum f.sp.cubense(FOC),is one of the most destructive diseases that can afflict banana plants.Applying biocontrol agents and practicing suitable rotation management are among the leading methods for controlling this disease.In this study,we screened a Bacillus strain W19 from the rhizosphere of a continuously cropped soil and also investigate its ability to promote plant growth and control Fusarium wilt of banana plants when fermented with organic fertilizers.Then,the influence of two-year crop rotation systems of pineapple-banana and maize-banana on the population density of FOC and soil microbial community structure was investigated to identify which rotation system was more effective in FOC suppression and differences in microbial community composition among different rotations.At last,the combined effects of pineapple-banana rotation and bio-organic fertilizer(BIO)application on banana Fusarium wilt disease and microbial communities were identified.The results were obtained as follows:1.Both pot and field experiments were carried out to evaluate the efficacy of the BIO on controlling banana Fusarium wilt disease and the results showed that application of BIO could significantly decrease the Fusarium wilt disease incidence.The efficacies of the BIO in pot experiment and in field experiment were 75%and 44%respectively.The fermentation broth and precipitated lipopeptides produced by W19 strain significantly inhibited the growth of FOC.The antifungal activity of the VOCs was 21%compared to the control.The precipitated lipopeptides analyzed by HPLC-MS showed that three homologs with antifungal activity including iturin,bacillomycin D and surfactin were produced by strain W19.The VOCs indentified by GC-MS showed that 18 VOCs produced by W19 strain with a significantly antagonistic effect on FOC.2.The application of BIO significantly promoted the growth and yield of banana.In pot experiment,after sixty days of growth,the BIO treatment significantly increased the fresh and dry weights of the banana plants by 22.6%and 34.6%,respectively,compared to the control.In two field trials,compared to the OF control,the BIO application increased the banana fruit weights by 1.89 kg tree-1,2.22 kg tree-1 and 8.48 t ha-1,10.48 t ha-1,respectively.The successful colonization of W19 was observed by both SEM and CLSM technology and the in situ colonization ability of PGPR strain 19 on the roots might be promoted by the banana root exudates.Besides,after three days incubation,a concentration of 7.35 mg l-1 indole-3-acetic acid(IAA)was determined in fermentation broth of W19.3.The soil bacterial and fungal communities of field experiment were analyzed using MiSeq platform to investigate the effect of BIO on soil microflora.The application of BIO increased the bacterial and fungal diversity.When compared to the soil sample collected from the control,BIO-treated soil revealed higher abundances of Acidobacteria,Firmicutes,Nitrospirae,Basidiomycota and Zygomycota.The abundance of Ascomycota was lower than that in control.At the genus level,BIO-treated soil revealed higher abundances of Bacillus,Gp1,Aspergillus,Penicillium and Mortierella.The abundance of Fusarium oxysporum was lower than that in control.In addition,Pearson correlation analysis indicated that the abundance of Fusarium oxysporum was positively correlated with the abundance of Bacteroidetes and Ascomycota but negatively correlated with the abundance of Gpl and Zygomycota.4.The investigation showed that FOC populations in the soil samples from pineapple treatments were significantly lower than those from maize treatments and the disease incidence of the Fusarium wilt from the banana season in the pineapple treatment was also significantly lower.Then,bacterial and fungal communities were interrogated by 454 pyrosequencing of the 16S rRNA gene and the internal transcribed spacer(ITS)region.Clustering analysis illustrated that the bacterial and fungal communities were similar among the sites under the same crop rotation system but significantly different between the two crop rotation systems.The OTU proportions and distribution of abundant OTUs showed that the fungal communities were more dissimilar between the two treatments than bacteria.Relative abundance of Basidiomycota,Glomeromycota,Acidobacteria,Planctomycete,Chloroflexi,Gp1,Gp2,Bradyrhizobium,Burkholderia and Planctomyces were significantly higher in pineapple treatment than in maize treatment,though Sordariomycetes,Actinobacteria,Gp3 and Firmicutes responded in an opposite fashion.Such changes might be important microbial factors in FOC suppression.5.The combined effects of pineapple rotation and BIO application on banana Fusarium wilt and microbial communities in field experiment were identified using MiSeq platform.The result showed that the disease incidence of pineapple rotation combined with BIO application was the lowest when compared with pineapple rotation only or banana continuous plantation.The relative abundances of Fusarium in different treatments were 10.07%in BOF treatment;6.50%in POF treatment and 4.79%in PBIO treatment.Significantly lower Fusarium abundances were observed in PBIO treatment.Moreover,treatment of PBIO increased the bacterial and fungal diversity when compared to the soil sample collected from the other treatments.The lowest bacterial and fungal diversity was observed in BOF treatment.RMT-based Network method was performed to compare the microbial ecological networks for each treatment.The result showed that the modularity in PBIO treatment was much higher than that in BOF treatment and POF treatments.Variance partitioning analysis(VPA)was used to determine the relative contributions of cultivation way,fertilizers and soil characteristics to the bacterial and fungal communities.The result showed that cultivation way explained the largest portions of the observed variation,which accounted for 4.19%and 5.12%in bacterial and fungal community structures,respectively.Just after cultivation way,the fertilizers also explained a large portion of the observed variation.Thus,the cultivation way was the most important factor in explaining the shifts in bacterial and fungal community structures.In conclusion,the application of BIO could significantly decrease the Fusarium wilt disease incidence in a low Fusarium wilt diseased soil.Pineapple-banana rotation was also an effective solution in suppression of Fusarium wilt disease.Disease incidence of Fusarium wilt was reduced to a much greater extent when pineapple-banana rotation was practiced together with BIO application.Both the two strategies could increase the Aplha diversity of soil microbial communities.The relative abundances of Basidiomycota and Zygomycota were increased by the two strategies though Ascomycota and Firmicutes responded in an opposite fashion.The modularity of PBIO treatment was much higher than that in BOF and POF treatments.The cultivation way was the most important factor in explaining the shifts in bacterial and fungal community structures.