Identification And Pathogenicity Of The Suspected Australian Strain Of Fusarium Oxysporum F. Sp. Vasinfectum

Fusarium wilt of cotton caused by Fusarium oxysporum f. sp. vasinfectum (FOV) is aworldwide disease.8physiological races had been described throughout the world, andraces3,7and8were reported in the China. Race7was the most predominant race in ourcountry. Our previous studies showed that there are3new types of FOV found in Hebeiprovince. Gene sequence analysis indicated that the3new FOV strains were closer withthe Australian FOV than races3,7and8collected from our country. Understanding thepathogenic differentiation and genetic diversity of the3new FOV strains is very importantfor the integrated control of cotton breeding and cotton blight.Genetic diversity of nine isolates, including physiological races3,7,8, two testedisolates from the field and Australian isolate, were evaluated by AFLP. We discovered greatgenetic diversity among the0.64to0.93genetic distance of tested isolates. Phylogenetictree divided four genetic groups (AGsⅠto AGsⅣ) based on0.71level of Dice similaritycoefficients. AGsⅠcoverd one isolate of representing physiological race3, AGsⅡcoverdone isolate of representing physiological race7and two tested isolates; AGsⅢ includedone isolate of representing physiological race8. AGs Ⅳ included the new3strains and theAustralian isolate, which were other than representing physiological races3,7and8ofFOV from China. Therefore, the new FOV strain were more related with the Australianisolate.The nine isolates were valued by the DNA sequences. The new FOV strain had greathomology with the Australian isolate by the sequences of EF-1α, PHO, and BT genes.Therefore, the new FOV strain were more related with the Australian isolate.Studing on the heredity differentiation of the vegetative compatibility group(VCG),the experiment results indicated that the nine isolates belong to four different VCGs (Ⅰ,Ⅱ,Ⅲ,Ⅳ,Ⅳ): race3and race8, we named VCGⅠand VCGⅡ, respectively; race7and twotested isolates in the third group, and we named VCGⅢ; The new FOV strain in the fourthgroup,they are compatible to Australian isolate and incompatible to race3, race7and race8, and we named VCGⅣ.The VCG experiment results indicated that the new FOV straingenetic relationship compared with Australian isolate is nearer than3,7,8race standard isolates.All the8tested FOV isolates were evaluated for the pathogenicity in different conttoncultivars, excepting the Australian isolate. Results indicated that the pathogenicity weredifferent among a susceptible wild cotton cultivar Jimian11, a moderately tolerant cottoncultivar Jimian169, a highly resistance cotton cultivar Zhongzhi mian2and sea-islandPima-51cotton cultivar, meanwhile three different pathogenicity groups (high, middle,weak) were surveyed. race3, race7and race8belong to the moderate pathogenicity group,and the disease index were above37.00. The new strain and Australian isolate belong tothe weak pathogenicity group and the disease index were under25.00. In Jimian169andsea-island Pima-51, toxicity difference was not obvious, and the pathogenicity were allweak. But there were obvious toxicity difference in different strains in the Zhongzhi mian2. The results showed that the new FOV strain is weaker than the pathogenicity of race3,7and8in our country.Biological characteristics of the pathogenic fungus causing wilt disease in cotton werestudied. The results showed that not all of the tested FOV isolates could grow on mediatested. The fungus could grow under20~35℃, with the optimum at30℃and pH4.5~10,with the optimum at pH6.5~7.5. The new FOV strain showed no difference at differenttemperatures and pH.