Study On Soil Microbial Diversity In Wards Infected By Banana Fusarium Wilt

Banana fusarium wilt, also known as Panama disease and yellow leaf disease, is a devastating fungal disease by Fusarium oxysporum f.sp.cubense infecting lead to necrosis of banana vascular. It is one of the most widely distributed and the most devastating disease of plants in the world’s agricultural history records, but also one of the important diseases of seriously threat to banana production in Southern China area at current. Banana fusarium wilt is very adptative in different areas, the speed of transmission is very fast. However, there is no effective method of prevention in the present. Ecological control of banana fusarium wilt is considered to be a promising field control method.Forty-six rhizosphere and non-rhizosphere soil samples were collected from three typical plots infected by banana fusarium wilt (Jianfeng, Shiyuetian,Chongpo) and two healthy banana plots (Lingao,Guangzhou) to study the microbial species diversity, the microbial community functional diversity and bacteria genetic diversity. At the same time, the correlation between soil factors and occurring of banana fusarium wilt was also analysised. The research result would provide technical and theoretical basis for explaining the pathogenesis of banana fusarium wilt and controlling its incidence by applying microbial ecology to regulate soil environmental measures. The results are as follows:1. Nineteen physical and chemical factors of forty six rhizosphere and non-rhizosphere soil samples from five banana plots were determined. The results showed that:(1) Most of the physical and chemical index and nutrient concentrations of rhizosphere and non-rhizosphere soils from healthy banana plots were higher than the diseased plots. In addition to the concentrations of soil sand and the available manganese, the other soil physical and chemical properties and nutrient concentrations were expressed as healthy plots higher than the diseased plots. Especially in the concentrations of clay soil, organic matter, cation exchange capacity, total nitrogen, total phosphorus, available phosphorus, available copper, available iron, available boron and exchangeable calcium were more obvious. And their concentrations in healthy banana plots were1.5times of the diseased plots.(2) In the same diseased plot, the value of pH in rhizosphere soils gradually increased with increasing of infection grades of banana plants, while the concentrations of available phosphorus and available boron gradually decreased with increasing of infection grades of banana plants. (3) Most concentrations of physical and chemical indicators in rhizosphere soils were higher than those of non-rhizosphere soils. Especially the value of pH and concentrations of organic matter, CEC, available nitrogen, total phosphorus, available phosphorus, available potassium, available manganese and available boron in rhizosphere soils were significantly higher than those of non-rhizosphere soils.(4) Similarity analysis results showed that there was significant correlation between the soil physical and chemical properties and the geographical presence of banana plots, while there were no direct correlation between banana fusarium wilt occurred weather or not and the soil physical and chemical properties and nutrient concentrations.2. The microbial species diversity of rhizosphere and non-rhizosphere soils from five banana plots was studied using the traditional microbial counting method. The results indicated that:(1) The numbers of culturable bacteria, actinomyces and fungi in rhizosphere and non-rhizosphere soils from the diseased banana plots were lower than those of the healthy plots, whereas pathogenic bacteria numbers were significantly higher than those in healthy plots. The species of bacteria and fungi in rhizosphere soils from the diseased plots were higher than the healthy ones.Similarity analysis results indicated that there was no significant relationship between banana fusarium wilt occurred and the species and numbers of cultured microbial in banana plantations.(2) The numbers and species of culturable bacteria, actinomyces and fungi in rhizosphere and non-rhizosphere soils from different infection grades plants in the same banana plot were also lower than healthy plants, declined with increasing of infection grades of banana plants. The numbers of pathogenic bacteria in rhizosphere and non-rhizosphere soils were increased with plant infection grade increasing in three plots infected by banana fusarium wilt. Similarity analysis results showed that there were obvious correlation between the infection grades of banana plants and the species and numbers of cultured microbe.(3) The numbers of cultured microorganism in rhizosphere soils from five different banana plots significantly higher than those in non-rhizosphere soils, which refected the rhizosphere effect that was the most significant factor for infected plants.(4) The change of cultured microbial community structure is an important feature of occurrence for banana fusarium wilt. Available phosphorus is the key soil factor effecting cultured microbial community structure in soils of wards infected by banana fusarium wilt.3. Microbial community functional diversity of rhizosphere and non-rhizosphere soils from five banana plots was studied by Biolog-ECO micro-tablet technology. The results showed that:(1) The microbial community functional diversity of rhizosphere and non-rhizosphere soils from diseased plots was lower than that of the healthy plots. The metabolic characteristics of microbial communities were no significant changes between different plots. The dominant communities of carbon metabolism were the groups of amine/amino compound and amino acid metabolism.(2) The microbial community functional diversity of rhizosphere and non-rhizosphere soils from different infection grades plants in the same banana plot was also lower than healthy plants, and declined with increasing of infection grades of plants. The characteristics of microbial community metabolism obviously changed between the rhizosphere and non-rhizosphere soils from infected plants and that of healthy plants in the same plot.(3) The decreasing of the soil microbial community functional diversity is an important feature of occurrence for banana fusarium wilt. Available boron was the key soil factor of effecting microbial community functional diversity in soils of wards infected by banana fusarium wilt.4. The bacterial genetic diversity of rhizosphere and non-rhizosphere soils from five banana plots, the mixed soils of rhizosphere and non-rhizosphere from different infection grades plants in three diseased plots, which named as sick soil, and the mixed soils of rhizosphere and non-rhizosphere from healthy plants in three diseased plots, which named as healthy soil were studied by constructing16S rRNA gene clone libraries. The results indicated that:(1) The bacteria genetic diversity of rhizosphere and non-rhizosphere soils from plots infected by banana fusarium wilt was lower than that of the healthy plots. Firmicutes, Proteobacteria, Actinobacteria, Acidobacteria, Gemmatimonadetes, Planctomycetes, Cyanobacteria, Bacteroidetes and Verrucomicrobia were common bacterial taxa in banana plots. In addition, TM7, Chloroflexi are also presented in soil samples of healthy plots, where as the diseased plots are Nitrospia.(2) The bacteria genetic diversity of rhizosphere and non-rhizosphere soils from different infection grades plants in the same banana plot was lower than healthy plants.(3) The bacteria community structure obviously changed in soils from the diseased plots. The dominant groups are Firmicutes, followed by Proteobacteria in the diseased plots. However, the dominant groups are Proteobacteria, followed by Firmicutes in healthy plots. The proportion of Firmicutes in diseased plots was47%higher than that of healthy plots, but the Proteobacteria in the former was18%lower than the latter. The proportion of Firmicutes in the mixed soils of different infection grades plants in the same plots was11%higher than that of healthy soils, but Proteobacteria in the former was3%lower than the latter.(4) The increasing of Bacillus contents was the main feature of banana fusarium wilt occurred. The proportion of Bacillus in diseased plots and the mixed soils of different infection grades plants of same plots were17%and13%higher than healthy plots and non infected soils, respectively.