Effects Of Palmitic Acid On Soil Microorganisms In Watermelon Continuous Cropping System And Pathogenicity Of Fusarium Oxysporum F.sp. Niveum

Fusarium wilt is a kind of soil-borne disease caused by Fusarium oxyporum f.sp.niveum(FON).There has been reported that companion of watermelon with wheat suppressed fusarium wilt through regulating soil microbes.As the major composition of the root exudates from the wheat,palmitic acid content is positively related to disease suppression.But the effects of palmitic acid on soil microbial taxa is unknown in cultivation.Additionly,during the parasitism of FON in host root,the fusaric acid and plant cell wall degradation enzyme represent pathogenicity of FON.So it is necessary to study the effects of palmitic acid on pathogenicity of FON.Different concentrations of palmitic acid were added to pot soil to achieve final concentrations of 0 mmol/kg,0.5 mmol/kg,1.0 mmol/kg,1.5 mmol/kg soil DW so as to study the effects of palmitic acid on the diversity,community structure,taxa distribution of soil microorganisms in watermeln continuous cropping system.In addition,we also studied the effects of palmitic acid on pathogenicity of fusarium wilt in vitro.The main results of this study are as follows:(1)The results of pot experiment of watermelon fusarium wilt showed that 1.0 mmol/kg,1.5 mmol/kg palmitic acid significantly decreased disease incidence.(2)The results of abundance and diversity analysis of soil microorganisms showed that 0.5 mmol/kg,1.0 mmol/kg,1.5 mmol/kg palmitic acid significantly decreased the abundance and diversity of soil fungi at early stage.1.5 mmol/kg palmitic acid still significantly decreased the diversity of soil fungi at last stage.0.5 mmol/kg,1.0 mmol/kg,1.5 mmol/kg palmitic acid have no significant effect on the abundance and diversity of soil fungi at early stage.(3)The principal axis(PCo A)analysis results showed that palmitic acid at all concentrations changed soil fungal community structure at early and last stage.Palmitic acid at all concentrations also changed soil bacterial community structure at early stage.And the 1.0 mmol/kg palmitic acid still changed soil bacterial community structure at last stage.(4)Palmitic acid at all concentrations significantly increased the abundance of Zygomycota,whereas significantly decreased the abundance of Ascomycota at early and last stage.Palmitic acid at the concentration of 1.0 mmol/kg significantly decreased the abundance of Basidiomycota at early stage.0.5 mmol/kg,1.0 mmol/kg,1.5 mmol/kg palmitic acid significantly increased the abundance of Mrotierella,whereas significantly decreased the abundance of Cryptococcus at early stage.Meanwhile,palmitic acid at concentrations of 1.0 mmol/kg and 1.5 mmol/kg significantly decreased the abundance of Fusarium at early stage.Palmitic acid at concentrations of 1.0 mmol/kg and 1.5 mmol/kg significantly significantly increased the abundance of Proteobacteria,but significantly decreased the abundance of Bacteroidetes at early stage.Palmitic acid at the concentration of 0.5 mmol/kg also significantly decreased the abundance of Bacteroidetes at early stage.At the same time,1.0 mmol/kg significantly decreased the abundance of Gemmatimonadetes at early stage.(5)Correlation analysis between disease incidence of fusarium wilt and microbial taxa showed that disease incidence of fusarium wilt was negatively related with Zygomycota and Mortierella.(6)Pathogenicity experiment in vitro showed that palmitic acid controlled fusarium wilt was not over influencing pathogenicity of FON.