Studies On The Pathogenicity Differentiation And Biocontrol Of Alternaria Alternata

Tobacco brown spot caused by Alternaria alternate is one of the main diseases in maturation and harvest stageof tobacco leaves,lowering seriously the yield and quality of tobacco leaves.Based on the pathogenicity test of the isolates of the pathogenic fungus from different areas in Anhui Province,the pathogenicity differentiation,biological characteristics of the isolates with different pathogenicity,the five extracellular enzyme activities of A.alternate and their relationship to pathogenicity were investigated systematically;and the antagonism and the mechanism of Trichoderma harzianum TH-1 against the pathogen were explored in this paper.The main results are as follows.1 Studies on the pathogenicity differentiation of Alternaria alternata isolates in Anhui ProvinceSixteen strains of Alternaria alternata were collected and isolated from different regions in Anhui.The pathogenicity of these isolates to the tested tobacco variety K326 was studied by applying wounded inoculation in greenhouse.The result showed that there was significant difference in the average disease indices of the lesions caused by different isolates,suggesting that there was significant differentiation in pathogenicity of A. alternata strains to tobacco leaves among isolates.According to the average disease indices of the lesions on tobacco leaves,the pathogenicity of the all isolates was classified into four categories:strong,intermediate,weak and nonpathogenic.There were different pathogenic types of A.alternata isolates among different growing areas and in the same one,suggesting that the distribution of the pathogenic types of A.alternata isolates was related to their localities in a way.2 Studies on the biological characteristics of Alternaria alternata isolates with different pathogenicityBased on the pathogenicity test,the biological characteristics of A.alternata isolates with different pathogenicity were tested,repectively,to probe the relativities among the characters.The result showed that the mycelium growth rates,conidium production and toxin production of the strong pathogenic isolates were all greater than those of the middle-pathogenic type and weak pathogenic type of A.alternata significantly. 3 Studies on extracellular enzyme activity of Alternaria alternata and the relationship between extracellular enzyme activity and pathogenicityThe activities of five extracellular enzymes of Alternaria alternata and the relationship between extracellular enzyme activity and pathogenicity were studied.The result showed that the activities of amylase,cellulose,pectinase of the two strong pathogenic strains, GY41 and GZ5 were all greater than those of the intermediate-pathogenic and weak pathogenic strains significantly.However,there was no significant difference in the activities of laccase and guaiacol oxidase among the three pathogenic types of Alternaria alternate.4 Antagonic effects and mechanism of Trichoderma harzianum TH-1 agaist the pathogen of tobacco brown spotSlecting two strong pathogenicity strains of GY41 and GZ5 as supply strains,and tested the antagonism of Trichoderma TH-1 against GY41 and GZ5 by confrontation culture,cup and dish method and microscope observation.The results show that the inhibition rates were 68.90%and 66.95%,respectively,which is Trichoderma TH-1 against GY41 and GZ5.The mycelium of Trichoderma TH-1 could penetrate and enlace mycelium of GY41 through microscope observation,which shows that there is obvious superparasitism Trichoderma TH-1 to GY41.The test by cup and dish method showed that the inhibition that is 2500μL,1000μL,250μL treatments of Trichoderma TH-1 spore suspending against GY41 is 84.87%,78.78%,57.20%,respectively,but to GZ5 is 80%, 76.57%,56.76%,which shows that it has obvious inhibition Trichoderma TH-1 spore suspending against Alternaria alternata.The inhibition that is 2500μL,1000μL,250μL treatments of Trichoderma TH-1 supersession liquid to GY41 is 77.63%,60.26,40.11%, respectively,and the inhibition to GZ5 is 76.24%,57.6%,41.63%,respectively,so which shows it has obvious inhibition Trichoderma TH-1 supersession liquid to Alternaria alternata.So,it has antibiosis action mechanism Trichoderma TH-1 against Alternaria alternata.To sum up,the antagonism of Trichoderma to Alternaria alternata is multi-mechanism to carry out,such as competition,antibiosis,superparasitism and so on.