Inhibition Of Rhizosphere Microecological Mechanism Of Verticillium Wilt In Cotton By Surface Layer Reconstruction

Verticillium wilt belongs to one of the diseases that restrict cotton production,bringing great harm to the cotton industry and is called "the cancer of cotton".Surface layer reconstruction technology exerts a significant inhibitory effect on the occurrence of verticillium wilt in cotton.However,its mechanism still remains unclear.For ordinary rotary tillage comparison,the current work puts forward the change in dynamic monitoring soil environmental factors.In addition,the variation in content of soil nutrients and soil enzyme activity and soil culturable microbial number and verticillium wilt is tightly associated with the soil ecological factors.A health system aimed at revealing the pathogenesis of top layer reconstruction inhibition of cotton verticillium wilt is developed from three aspects,namely the change in the quantity of micro sclerotium bacteria from the dahlia branches,cotton rhizosphere micro ecological environment and cotton plants.The results are presented as follows:1.Field investigation showed that tillage reconstruction significantly reduced the incidence of verticillium wilt in cotton(the incidence of tillage reconstruction was65.36% and the control incidence was 95.53%)and the incidence index(the incidence of tillage reconstruction was 21.25% and the control was 35%).The growth of cotton aboveground and root system was stimulated.In the meanwhile,the volume and surface area of the root system increased obviously.Nevertheless,the yield did not alter in a significant way.2.Based on the results of the determination of the number of microsclerotia,in comparison with the control of rotary tillage,the microsclerotia in the 0～ 20 cm soil layer under the surface reconstruction treatment was notably decreased,while that in the 20～ 40 cm soil layer was drastically improved.In addition,there existed no obvious change in the soil layer below 60 cm,suggesting that in the surface layer of cotton field,the number of microsclerotia decreased significantly after surface layer reconstruction treatment.Although the number of microsclerotia increased somewhat after surface layer reconstruction treatment,the overall number of microsclerotia decreased significantly in the 0～40 cm soil layer where verticillium wilt was mainly distributed.3.The results of dynamic monitoring of soil environmental factors demonstrated that the surface layer reconstruction temperature in the early growth stage of cotton was higher than that of the control group.The shallow soil moisture content did not change significantly under the surface layer reconstruction,while the deep soil moisture content improved notably when it was compared with the rotary tillage control.Besides,the accumulative water capacity increased significantly.Surface layer reconstruction reduces soil bulk density,significantly increases porosity,and greatly improves soil permeability and aeration in cotton fields.4.According to the results of the determination of soil nutrient content and enzyme activity,in the 0～20 cm soil layer,the total content of reconstructed nutrients and the content of available nutrients in the surface layer decreased significantly compared with the control layer,while the content of available nutrients in the deep soil tended to increase.Surface layer reconstruction changes the spatial distribution structure of soil nutrients,making the vertical distribution of nutrients become more uniform.The activity of urease,sucrase and phosphatase reconstructed in the surface layer reduced in the 0～20 cm soil layer while the activity of urease,sucrase and phosphatase increased obviously in the 20～40 cm soil layer.Besides,the enzyme activity was drastically added in the soil layer below 40 cm.5.Plate culture results of soil culturable microorganisms demonstrated that during the whole growth period of cotton,the number of bacteria,fungi and actinomycetes in the 0～ 20 cm soil layer treated by surface reconstruction was lower than that of the control group.However,the number of bacteria,fungi and actinomycetes in the 20～60cm soil layer was higher in comparison with the control group.There existed no significant difference below 60 cm.Under the treatment of topsoil reconstruction,the number of bacteria in the 0～40 cm soil layer enhanced while the number of fungi significantly decreased,implying that the transformation from fungal soil to bacterial soil contributes to inhibiting the survival and occurrence of soil pathogenic bacteria.To conclude,surface reconstruction reduces the number of microsclerotia in the0～40 cm soil layer,and decreases the probability of initial infection.Soil porosity,especially non-capillary porosity,significantly increased soil permeability and aeration,improved the rhizosphere growth environment of cotton plants,and significantly promoted the growth of overland and root systems,which was conductive to improving the resistance of plants to verticillium wilt.The cultivation of actinomycetes,bacteria and fungi in the topsoil can gradually replace the fungal soil,which caneffectively inhibit the occurrence of verticillium wilt in cotton.