香榧果实褐斑病病原菌鉴定及防治药剂筛选

Identification of brown spot on fruit of Torreya grandis and screening of fungicides

为明确近年来在香榧Torreya grandis果实上出现的一种新病害——褐斑病的病原菌,通过分离物致病性测定、形态学观察、rDNA-ITS序列分析及病原菌生物学特性进行鉴定,并对苯醚甲环唑、嘧菌酯、甲基硫菌灵、咪鲜胺、肟菌酯及吡唑醚菌酯6种防治药剂进行了初步筛选。结果表明,从病样中分离到的菌株XF01在回接试验出现的症状与田间自然感病症状一致,证明菌株XF01为香榧果实褐斑病的致病菌。该病原菌菌丝初为灰白色,后为深灰色或青褐色;分生孢子梗单生或簇生,无分枝,淡褐色;分生孢子多倒梨形或卵形,大小平均为19.258μm×9.048μm,横、纵隔膜分别为1~7个和0~3个,无喙或具柱状短喙,形态特征与链格孢菌Alternaria alternata一致。该菌ITS序列(Gen Bank登录号为KU525533)与链格孢菌株ITS序列(Gen Bank登录号为KR864893.1)同源性为100%,并聚为一簇,分子鉴定结果与形态学鉴定结果一致,确定引起该病害的病原菌为链格孢菌。该病菌菌丝生长、产孢和孢子萌发的最佳温度均为28℃,最适生长pH均为7。室内毒力测定结果显示,咪鲜胺对该菌菌丝生长的抑制效果最好,EC50为0.065μg/mL;吡唑醚菌酯对其孢子萌发的抑制效果最好,EC50为0.002μg/mL,表明这2种药剂可用于香榧果实褐斑病的田间防治。

A new disease, brown spot, appeared recently on fruits of Torreya grandis. In order to clarify the causal agent of brown spot, the pathogenic fungus was identified based on the analysis of pathogenicity tests of isolates, morphological characteristics, rDNA-ITS sequence and biological characteristics. And the inhibitory effect of six fungicides（difenoconazole, azoxystrobin, thiophonate-methyl, prochloraz, trifloxystrobin and pyraclostrobin） to T. grandis were determined. The strain XF01 was separated from brown spot disease fruits of T. grandis, and was identified as the pathogenic fungus by Koch＇s law. Colonies of the pathogen on PDA were initially gray white, and later was dark gray or green brown; conidiophores solitary or clustered, without branching, brown; conidia were obpyriform or oval,the average size of spore body 19.258 μm×9.048 μm, with 1-7 tabulae, 0-3 mediastina, columnar beaks or no; these characteristics consistent with Alternaria alternata. The ITS sequence of XF01（accession no. KU525533） analysis showed 100% similarity with A. alternata（accession no. KR864893.1）, and clustered in the same branch; morphological and molecular proofs indicated that brown spot disease was caused by A. alternata. The optimum temperature of mycelium growth and spore germination of the pathogen was 28℃, and the optimum pH of 7. Indoor toxicity test results showed that the prochloraz had the best inhibiting effect on mycelial growth, with the EC50 of 0.065 μg/mL, while pyraclostrobin had best inhibitory effect than others on spore germination, with the EC_（50） of 0.002 μg/mL. The two fungicides could be used to control brown spot of T. grandis in the field.