软腐病病原菌对金钗石斛致病性的形态学研究

摘要

Objective To investigate the morphological characteristics of Dendrobium nobile due to the damping-off disease caused by Pythium ultimum. Methods The pathogenic experiment on D. nobile was conducted using P. ultimum spore suspension spraying method. Then the differences of the healthy and the diseased D. nobile leaf tissue infected by P. ultimum for 48 hrs were observed using the free-hand sectioning by microscope. In addition, the different characteristics of the root, the stem and the leaf between the healthy and the diseased D. nobile infected by P. ultimum for 48 hrs were observed using scanning electronic microscope (SEM). Results Due to the observation using free-hand sectioning, the healthy leaf kept intact. However, in the diseased group, a lot of P. ultimum mycelia were found inside the D. nobile leaf tissue. There were many oospores and sporangia residing in the mesophyll cells of D. nobile. The integrity of the mesophyll cells was seriously destroyed. The observation of the scanning electronic microscope indicated that the mesophyll cells, the sheath tissue, the root tip cells and the root sheath were easily infected by the pathogenic fungus. The pathogenic fungal mycelia in the stem digested and degraded the cells, and entered the other tissues. In the root site, the fungal mycelia infected the host plant in the same way as it did in the stem site on the one hand and entered the host plant through the holes of the velamen as well. P. ultimum mycelia went into the D. nobile through the stomas of the surface and the opposite side of the leaf tissue with great destroyed effects. At the same time, the specific structure appressorium formed. Conclusion P. ultimum infects D. nobile by mechanical penertrating and secreting degraded enzymes to destroy the host cell walls and its internal structure.%目的旨在研究软腐病病原菌终极腐霉对金钗石斛致病的形态学特征。　　方法利用终极腐霉孢子悬液喷洒法对金钗石斛组培苗叶片进行致病性实验，对健康的以及感染终极腐霉48 h 后的金钗石斛的叶片应用水压片法在光学显微镜下观察两者的形态差别。对健康的金钗石斛及感染终极腐霉48 h 后的植株的根、茎、叶进行扫描电镜观察并分别比较致病前后微观结构的差异。　　结果压片法观察叶片部位结果显示，健康的金钗石斛叶片结构完整；致病组可见终极腐霉病原菌在金钗石斛叶片中生长旺盛，大量卵孢子和孢子囊分布于叶肉细胞间。感染病原菌后的叶肉细胞完整性受到严重破坏。扫描显微镜观察结果显示：叶肉细胞、叶鞘组织、幼嫩根尖细胞以及根被为发病的关键部位。在茎部菌丝通过消解细胞壁进入细胞。在根部菌丝除通过消解细胞壁进入细胞外，还通过根被表面的许多孔洞进入细胞。病原菌菌丝体通过叶背面大量分布的气孔结构或叶表面极具破坏性地进入叶片体内，并形成典型的附着胞结构。　　结论终极腐霉主要通过机械穿透和分泌降解酶破坏寄主细胞的细胞壁及其内部结构。