Study On Characterstics And Biological Control Of Clubroot Disease In Taibai Area

The clubroot disease is a cruciferous soil-borne disease caused by the infection of Plasmodiophora brassicae Woron causes serious damages to roots,which directly affect nutrients absorption and water transport,consequently results in nutrition deficiency and wilting of crops,and even plant death under extreme conditions.Taibai County has become the main planting area of?alpine vegetables?in Shaanxi Province due to its favorable climate conditions.Vegetable cultivation has also become a local leading industry.However,with the expansion of cruciferous vegetables and their consistent growth on same soil in recent years,clubroot disease is becoming more and more serious,restricting the development of the vegetable industry.In this study,we used the clubroot disease of vegetable growing area in Taibai County as the research object,to identify the physiological race types of clubroot disease,as well as to research the effects of different concentrations and infect period of pathogens on the pathogenesis of clubroot disease,and research the changes in the composition and structure of rhizosphere microbial communities.To research the prevention and control effects of biocontrol strains and microbial fertilizers on clubroot pathogens were studied through pot and field experiments.The main results are as followed:?1?The physiological race type of pathogen of clubroot disease in Taibai area was physiological race No.7.The pot experiment showed that:?1?:Clubroot disease was most susceptible to infection by rhizoctoma at 10 days after the growth of first true leaf of Chinese cabbage and was the highest at 10⁸ cfu·ml^-1 at the concentrations of pathogens.?2?:The disease rate of clubroot diseases was positively correlated with respiratory rate and stomatal conductance.the photosynthesis,as well as the growth of plants decreased after infection with clubroot disease,while respiration increased.?3?:Cabbage plant defense enzymes POD,PAL,PPO were negatively correlated with the disease rate,malondialdehyde content was positively correlated with the incidence rate,and resistance to plant diseases was damaged.?2?Analysis of microbial population structural diversity showed that:?1?:The number of bacterial OTU in the rhizosphere of cabbage was significantly lower than that of uninfected cabbage,and the bacterial population diversity decreased with the increase of the disease degree,while the fungal population diversity increased;?2?:There was a significant difference between the infected plants and uninfected on the bacterial and fungal community structure.In the bacterial community,the relative abundance of Actinobacteria decreased with the incidence rate,A2,A3 and A4 decreased by 40.28%,43.12%and 46.05%,respectively.However,in the fungal community,the A2,A3 and A4 whose relative abundance of Ascomycotain increased by106.12%,92.92%and 83.50%respectively;?3?:The obtained rhizosphere fungal populations were classified according to their functional types.The relative abundance of OTU of rhizosphere pathogens increases with the disease level in cabbage.?3?Strain SP12 was isolated from rhizosphere soil of healthy plants,with good control effect against clubroot disease.The preliminary identification result showed that the strain was Streptomyces alboflavus.were studied to inhibit disease and promote growth of some biocontrol strains from the Lab.The results showed that:?1?:SP12 and D74 can significantly reduce the disease rate and disease index of clubroot disease,and the disease rate was decreased by 50.0%and 41.7%,respectively,while the disease index decreased by 20.3%and 19.4%;?2?:Improved the fresh weight of cabbage ground part 36.6%and 8.6%,the aboveground part increased by25.4%and 4.9%respectively;?3?:SP12 and D74 increased the root activity by 46.2%and34.4%,respectively,PPO activity was significantly increased by 49.0%and 66.5%,respectively,and the proline content increased significantly by 11.2.%and 35.1%,MDA content decreased significantly by 5.2%and 7.4%,respectively;SP12 treatment increased POD activity,which increased by 26.4%.?4?:SP12 and D74 could changed the microbial community structure of rhizosphere soil of Chinese cabbage,and increase the number of Actinomycetes by 63.7%and15.4%.In summary,SP12 and D74 can prevent and cure cabbage clubroot disease by improving plant resistance and rhizosphere microbial community structure.?4?Field experiments showed that:?1?:Application of microbial fertilizer could significantly promote the growth of cabbage,with maximum increase observed with root+foliar application,total weight,bulb diameter,bulb mass and moisture content were increased by18.3%,9.4%,22.8.%and 8.0%,respectively;The content of Vc,cellulose and starch in cabbage also increased on different levels.?2?:Determination of gene expression in cabbage plants by different fertilization treatments,Compared with root application,the expression of some genes related to resistance to clubroot was significantly higher in foliar application.such as clubroot disease resistance gene?BoCR9.1?,plant resistance gene?pdf1.2?,disease path protein?PR5?,cytochrome C oxidase?COX11?.It is indicated that foliar application can promote the expression of resistant genes of clubroot disease and improve the resistance of plants to clubroot disease.In summary,this study identified the pathogen of clubroot disease in Taibai area as the physiological race of No.7.The occurrence of clubroot disease will lead to the change of rhizosphere micro-ecology,which will reduce the bacterial population,especially the beneficial microorganisms such as actinomycetes.As the population of fungus population decreases,the number of harmful pathogens in the fungus increases,which results in the destruction of the micro-ecological balance.Pot experiments showed that the best period of infection of Chinese cabbage was 10 days after the emergence of true leaves,and the optimal infestation concentration was 10⁸ cfu·ml^-1,and D74 and SP12 were good for the prevention and control of clubroot disease.It is significantly reduce that the disease rate and disease index of clubroot disease.In the Taibai area,the application of microbial fertilizer and foliar application of microbial fertilizer,both treatments have a promoting effect on cabbage growth,nutrient accumulation and enhance activities of resistant enzyme,and foliar application of microbial fertilizer can significantly improve expression resistance genes such as BoCR9.1,pdf1.2 and COX11 to enhance the resistance of cabbage plants to infection by clubroot disease.