苹果炭疽叶枯病病原Glomerella cingulata及其侵染过程

为明确苹果炭疽叶枯病病原菌围小丛壳Glomerella cingulata的侵染致病特征,在分离获得该病原菌的基础上,采用形态学观察、ITS序列分析和致病性测定对其进行了鉴定,并利用光学和扫描电子显微镜对病原菌在嘎啦苹果叶片上的侵染过程进行了研究.结果表明,在陕西咸阳地区分离获得的9株病原菌均为围小丛壳G.cingulata.25 ℃下接种9 h后,分生孢子中间产生隔膜,双胞化,并萌发产生芽管和附着胞;24 h后分生孢子的2个细胞均可萌发并形成芽管及附着胞,部分芽管顶端可产生次级分生孢子;48 h后次级分生孢子萌发形成附着胞;72 h后,附着胞下形成的侵染钉可直接入侵寄主,在表皮细胞内形成初生菌丝和次生菌丝,此时叶片表面已出现褐色斑点.接种7 d后叶片病斑处出现分生孢子盘和子囊壳.表明陕西省近年出现的苹果炭疽叶枯病病原菌为围小丛壳G.cingulata,该病菌在嘎啦叶片上的一些特殊侵染行为可能是导致该病害易在短时间内暴发的重要原因.

Etiology and infection process of Glomerella cingulata causing Glomerella leaf spot of apple

In order to investigate the pathogenicity characteristics of Glomerella cingulata causing Glomerella leaf spot of apple, the pathogen was firstly isolated and identified using morphology, ITS sequence and pathogenicity analyses, and the infection process of the pathogen was studied by means of optical and scanning electron microscopy. Nine strains isolated from diseased leaves in Shaanxi Province were identified as G.cingulata. The infection process of G.cingulata observed by microscopy showed that conidia produced one septum at the middle of the conidia, then germinated and formed germ tubes and appressoria on the leaves of Malus domestica cv.Gala at 9 hours after inoculation (hai). Both cells of the conidia germinated and formed germ tubes and appressoria at 24 hai. The single-celled secondary conidia were developed at the distal ends of some germ tubes at 24 hai. The secondary conidia germinated and produced appressoria at 48 hai. The fungus penetrated leaf cuticle and epidermal cells directly by infection pegs formed by appressoria, and then formed primary hyphae and secondary hyphae in host epidermal cells at 72 hai. At this time, small brown spots appeared on inoculated leaves. About 7 days after inoculation, both the acervuli and perithecia were formed on the inoculated leaves. These results suggest that the pathogen of glomerella leaf spot of apple in Shaanxi is G.cingulata, and the special infection behaviors of this pathogen on the leaves of cv.Gala may explain this phenomenon that this disease could break out in a short period.