瓜拟多隔孢引起的砂田西瓜叶疫病

Watermelon foliar blight caused by Stagonosporopsis cucurbitacearum in gravel-mulched field

近年来,甘肃省白银市靖远县的一些砂田西瓜中出现了严重的叶疫病,严重田块病株率超过70%。2018年7月,从靖远县高湾乡罹病西瓜叶片上分离得到拟多隔孢属Stagonosporopsis真菌,病叶检出率达100%。采用离体叶片和植株接种法评价单孢分离菌株XG-3对西瓜和甜瓜的致病性,所有接种处理在24 h内均发病显症而对照未发病,其中发病叶片原接种菌的检出率为100%。菌株XG-3在PDA和OA平板培养基上20和25℃培养20 d,未见产孢。在自然感病的西瓜叶片上观察到少量分生孢子器,在人工接种发病的西瓜和甜瓜茎、叶上产生大量分生孢子器和分生孢子:分生孢子器球形至亚球形,大小为(82.4~243.3)μm×(82.4~188.4)μm,分生孢子器具1~2个孔口,孔口直径15.7~27.5μm;分生孢子无色,0~3个隔膜,杆状、柱状、长椭圆形、花生形及不规则形,直或稍弯曲,分隔处不缢缩或缢缩,大小为(5.2~28.3)μm×(2.2~6.0)μm,分生孢子形态和大小依基质和环境条件的不同而有较大差异。BLASTn分析结果显示,菌株XG-3(GenBank登录号:MW282128)的rDNA-ITS序列与瓜拟多隔孢Sta.cucurbitacearum分离物287ITS(GenBank登录号:AY293804.1)的序列相似性达99.80%。在基于rDNA-ITS构建的系统发育树中,菌株XG-3与Sta.cucurbitacearum聚为一组,与西瓜拟多隔孢Sta.citrulli和木瓜拟多隔孢Sta.caricae区分开来。依据病菌形态学和分子生物学特征,将菌株XG-3鉴定为瓜拟多隔孢Sta.cucurbitacearum[Basionym:Sphaeria cucurbitacearum]。

In recent years, severe foliar blight appeared on watermelon in some gravel-mulched fields in Jingyuan County, Baiyin City, Gansu Province, with the disease incidence more than 70% in serious fields. In July 2018, some fungal isolates of Stagonosporopsis were isolated from the diseased leaves of watermelon in Gaowan Township, Jingyuan County, with a 100% isolation rate. The pathogenicity of isolate XG-3 was tested on watermelon and melon by artificial inoculation on detached leaves and plants. All inoculation treatments showed the diseased symptom within 24 h, while the control did not be infected. The re-isolation rate of the original isolate reached 100% in infected leaves, thereby fulfilling the Koch’s Postulates. Sporulation was not observed when isolate XG-3 was cultured on PDA and OA plates for 20 d at 20 ℃ and 25 ℃. A small amount of pycnidia was observed on the naturally infected leaves of watermelon, however abundant pycnidia produced on the diseased stems and leaves of watermelon and muskmelon by artificially inoculation. The pycnidia were sphe-rical to subspherical,(82.4-243.3) μm ×(82.4-188.4) μm, with 1 to 2 ostioles, and the ostiole’s diameters were 15.7-27.5 μm. Conidia were colorless, 0-3 septa, rod-shaped, columnar, ellipsoidal, oblong, peanut-shaped and irregular shape, straight or slightly curved, constricted or not at the septum, and(5.2-28.3) μm ×(2.2-6.0) μm. Type and size of conidia varied with substrates and infection conditions. BLASTn analysis showed that the rDNA-ITS sequences of isolate XG-3(GenBank accession No. MW282128) had a 99.80% similarity with Sta. cucurbitacearum isolate 287 ITS(GenBank accession No. AY293804.1). Phylogenetic analysis based on rDNA-ITS sequences placed isolate XG-3 in group Sta. cucurbitacearum, separated from Sta. citrulli and Sta. caricae. Isolate XG-3 was identified as Sta. cucurbitacearum [Basionym: Sphaeria cucurbitacearum] by morphological and molecular biological characters.