| Watermelon Fusarium wilt as a serious plant disease worldwide was infected from the pathogenic fungus Fusarium oxysporum f.sp.niveum（FON）,which negatively restrains watermelon production worldwide.Once infected,the pathogen of Fusarium wilt can survive in the soil for many years,severely restricting the watermelon industry of China.Thus,the suppression of watermelon soil-borne diseases is an extremely urgent matter.The activities of soil microorganisms are closely related to soil health and agricultural production.Their metabolic activities not only affect the material cycle and ecological balance,but also promote the development of soil fertility and the transformation of plant nutrients.The composition and diversity of soil microbial communities is closely related to the soil-borne disease.Therefore,the basis for the suppression of watermelon Fusarium wilt is regulating the high-incidence soil microflora,constructing a healthy soil microflora and analyzing the potential disease suppression mechanism by dazomet fumigation combined with bio-organic fertilizer.In this research,dazomet fumigation combined with bio-organic fertilizer was proposed to suppress watermelon Fusarium wilt,which was verified by field and laboratory experiments.We used dilution coating technology,soil physical and chemical properties determination and high-throughput sequencing to explore 1)the effect of dazomet fumigation combined with bio-organic fertilizer on watermelon field effect,2)the effect of dazomet fumigation combined with bio-organic fertilizer on the soil microbial flora and its potential soil microbial ecological mechanism,3)the primary factors affecting the colonization of the antagonistic Bacillus amyloliquefaciens SQR9 in the soil,4)the primary driving factors and the community construction mechanism of the new soil microflora,in order to explore the characteristics of healthy watermelon soil microbial community and the potential ecological mechanism of constructing healthy soil microbial community.The main findings are as follows:1.Dazomet fumigation combined with bio-organic fertilizer was applied in a watermelon field with a high incidence of watermelon Fusarium wilt,and the suppression promotion effect of dazomet fumigation combined with bio-organic fertilizer on watermelon Fusarium wilt was evaluated.Dazomet fumigation combined with bio-organic fertilizer significantly reduced the incidence of watermelon fusarium wilt with the disease incidence of three seasons was as low as 13%,40%,and 17%,respectively.Compared with non-fumigation treatment,dazomet fumigation combined with bio-organic fertilizer significantly increased the yield of watermelon,increasing by 64.1%,63.5%and 231%respectively in the three seasons.Choose the soil samples from the first season for the analysis of soil physical and chemical properties,the result indicated that the disease incidence of watermelon Fusarium wilt was significantly correlated with soil physical and chemical properties.In addition,the utilization rate of nitrogen,phosphorus,and potassium in dazomet fumigation combined with bio-organic fertilizer treatment were 19.87%,4.61%and 24.93%,which were significantly higher than other treatments,and its nutrient dependence rate was significantly lower than other treatments,indicating that dazomet fumigation combined with bio-organic fertilizer was beneficial to improve the absorption of soil nutrients by watermelon plants.Dazomet fumigation combined with bio-organic fertilizer significantly reduced the number of Fusarium oxysporum in the soil,indicating that it can effectively inhibit the growth of pathogenic microorganisms.Watermelon samples were collected after harvest and the results showed that dazomet fumigation combined with bio-organic fertilizer significantly increase the soluble protein and vitamin C content of watermelon thus improve the quality of watermelon.2.The soil samples of the first season were selected for high-throughput sequencing to evaluate the effects of dazomet fumigation combined with bio-organic fertilizer on the composition and diversity of soil microbial communities and the potential microbiological mechanisms for the suppression of watermelon Fusarium wilt.Our results showed that the disease incidence of watermelon Fusarium wilt was significantly correlated with soil microbial community composition.Dazomet fumigation combined with bio-organic fertilizer significantly reduced the abundance and diversity of soil bacterial and fungal communities,and also changed the composition of the soil microbial community.In the bacterial community,dazomet fumigation combined with bio-organic fertilizer significantly increased the relative abundance of Firmicutes,TM7,Gemmatimonadetes,and Actinobacteria and reduced the relative abundance of Actinobacteria.In the fungal community,dazomet fumigation combined with bio-organic fertilizer significantly increased the relative abundance of Trichoderma.The abundance of Fusarium in the treatment with only organic fertilizer was higher than other treatments.The network analysis results showed that the soil microbial ecological network treated by dazomet fumigation combined with bio-organic fertilizer was more complex and more closely connected than other treatment.The application of bio-organic fertilizer after fumigation of dazomet can promote the restoration of soil microbial community.The beneficial microorganisms in bio-organic fertilizer have become the key groups in the soil microbial community network.These groups play an important role in the suppression of watermelon Fusarium wilt.3.A microcosmic experiment was set combined with high-throughput sequencing and dilution coating technology for exploring the primary factor affecting the colonization of the antagonistic Bacillus amyloliquefaciens SQR9 in soil.The results showed that dazomet fumigation significantly reduced the abundance and diversity of indigenous microbial communities,which was good for the colonization of the antagonistic SQR9 in the soil.The damaged soil microbial community gradually recovered with the increase of cultivation time after fumigation.The addition of bio-organic fertilizer effectively increased the diversity of the bacterial community and promoted the recovery of the soil microbial community.Dazomet fumigation combined with bio-organic fertilizer changed the composition of soil bacterial communities,which increased the relative abundance of Actinobacteria and Firmicutes and reduced the relative abundance of Acidobacteria.Pearson correlation analysis indicated that the Bacillus,which exogenously added strain SQR9 belongs to,was significantly positively correlated with Streptomyces and have a significant positive correlation with Kaistobacter,Candidatusm,etc.Dazomet fumigation combined with bio-organic fertilizer increased the colonization of the antagonistic SQR9 in the soil by dilution coating results.For further explore the potential factors of bio-organic fertilizer improving the colonization of SQR9 in soil,the bio-organic fertilizer was divided into the space niche and nutrient niche for microcosmic experiment.As the dosage of fumigant reached 375 kg ha-1（recommended dosage）,the colonization efficiency of SQR9was the best in the mixed treatment of nutrition and spatial niche,followed by nutritional niche and space niche separately added treatments.4.Through the microcosmic experiment combined with high-throughput sequencing,the effect of nutrition and spatial niche,as well as the abundance and diversity of bacterial communities on the construction of soil microbial flora were explored.The results showed that the abundance and diversity of the exogenous microbial communities and the spatial niche had no significant impact on the abundance and diversity of the newly constructed microbial community,but the addition of the exogenous nutrient niche significantly reduced the newly constructed microflora.The addition of nutrient niche also changed the structure and composition of the soil bacterial community,and the community in nutrient addition treatment performed more concentrated.Among all the treatments,the bacterial community composition appeared phylogenetic aggregation,and the nutritional niche is the most important driving factor affecting the relative abundance and phylogenetic composition of the soil bacterial community,followed by the spatial niche and the concentration of exogenous microbial community.In conclusion,the result of this study shows that dazomet fumigation combined with bio-organic fertilizer effective suppressed the watermelon Fusarium wilt disease and improved the yield and quality of watermelon.Dazomet fumigation destroyed the indigenous microbial community in the soil and released the niche occupied by the indigenous microbial community.The application of bio-organic fertilizer promoted the restoration of the soil microbial community,and the nutrition and spatial niche provided by bio-organic could improve the colonization of beneficial microorganism in the soil.Thus,the destroyed microbial flora restored to a healthy soil microbial community dominated by beneficial microorganism. |
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