禾谷镰刀菌在小麦穗部侵染过程的细胞学研究

 采用扫描和透射电镜技术系统地观察了禾谷镰刀菌(Fusarium graminearum)在小麦穗部的侵染过程。接种后6~12 h,分生孢子在小麦穗部的任何部位均可萌发,每个孢子可产生1至多个芽管,新产生的芽管并不立即入侵寄主组织,而是在寄主体表生长扩展;接种后36~48 h观察,小穗颖片、外稃、内稃的内侧和子房的表面形成了密集的菌丝网,然而在小麦穗轴表面、颖片和内稃的外表面,菌丝生长缓慢、分布稀疏,但颖片外表边缘的菌丝可跨越边缘扩展到颖片的内表皮上;接种后36 h,寄主体表菌丝产生入侵菌丝,以直接入侵方式由颖片、外稃、内稃的内侧及子房的顶部侵入寄主组织体内,随后,菌丝以胞间和胞内生长的方式向下扩展;接种后4~5 d,菌丝由上述组织扩展到达穗轴后,在穗轴内沿微管束组织和皮层组织向上和向下扩展,延伸到相邻小花,随菌丝在小麦穗部组织内不断地生长扩展,使得寄主细胞坏死、解体,并最终导致整个麦穗的枯死。

Cytology of infection process of Fusarium graminearum on wheat spikes

The infection process of Fusarium graminearum on wheat spikes was examined by scanning and transmission electron microscopy. Macroconidia of the pathogen germinated 6-12 h after inoculation on all parts of spike, and produced one or several germ tubes, which did not infect host tissues immediately, but continued to extend and branch on host surfaces. Hyphal networks were usually formed on inner surfaces of glume, lemma, palea and on ovary 36-48 h after inoculation. However, hyphae grew slowly and no hyphal network was formed on outer surfaces of glume, lemma and rachis. The hyphae on outer surfaces of glume could extend over edges to inner surfaces. Penetration of host tissues occurred on inner surfaces of glume, lemma, palea and on the upper part of ovary by infection hyphae 36 h after inoculation. The hyphae in these infected tissues then spread downward to rachis by inter- and intracellular growth. When the hyphae arrived at rachis 4-5 d after inoculation, they extended upward and downward to adjacent florets inter- and intracellularly in vascular bundles and cortical tissue of the rachis. Extension of the pathogen in wheat spike resulted in a series of pathogenic changes in host tissues, such as necrosis and degeneration of host cells, and decolourization and death of whole wheat spike.