Studies on biological characteristics and pathogenicity differentiation in Alternaria alternata in Anhui

The biological characteristics and pathogenicity differentiation of Alternaria alternate in Anhui were systematically investigated.Results showed that hyphae can grow from 10 ℃ to 35 ℃and the optimum temperature was from 25 ℃ to 30 ℃.Temperatures of lower than 7 ℃ or higher than 40 ℃ were not fit for mycelial growth.The lethal temperature of conidia was 53 ℃ for 5 min or 50 ℃ for 10 min,while that of hyphae was 52 ℃ for 5 min or 49 ℃ for 10 min.Pathogenic fungus can grow under condition of pH 4.0～6.0,showing double peak curve,with optimum at pH 6 and pH 8.0.The optimum pH for conidial production and mycelium growth were 6.0 and 8.0,respectively.It was benefitial for mycelial growth and concidial production under the condition of alternating between illumination and darkness.Results of pathogenicity study showed that there was significant differentiation in pathogenicity of A.alternata strains to tobacco leaves among isolates.According to average disease indices of lesions on tobacco leaves,the pathogenicity of 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 area,suggesting that the distribution of the pathogenic types of A.alternata isolates was related to their localities.