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Identification and Characterization of Brown Spot Disease on Fruit of Chinese Torreya

Zhang Shuya;Li Ling;Zhang Chuanqing

  Chinese torreya(Torreya grandis) is one of the important economic foresee crops in the hilly hills and mountain slopes naturally,particularly in Zhejiang province,south China.A new disease,brown spots,appeared on fruits of Torreya grandis recently.Initially,small dark brown spots and necrotic center lesion surrounded by a chlorotic halo appeared on fruit,and then the fruit shrank and fell off gradually with the development of disease.In order to clarify the causal agent of brown spot,the pathogenic fungus was identified based on the analysis of morphologic characteristics,rDNA-ITS sequences and pathogenicity tests.Colonies of the pathogen on PDA were initially gray white and dark gray or green brown gradually.Conidiophores of the fungus were solitary or clustered,without branching,and conidiophores were brown,obpyriform or oval.The average size of spores 19.258μm×9.048 μm,with 1~7 transverse septum,0~3 longitudinal septum,columnar beaks or no.These characteristics wereconsistent with Alternaria alternata.Sequence of rDNA-ITS(Accession no.KU525533) analysis showed 100%similarity with A.alternata from GenBank database.Taken together,both morphological and molecular proofs indicated that brown spot disease was caused by A.altemata.……