球孢白僵菌侵染玉米螟的电镜观察

Electron microscopic observations on Beauveria bassiana infecting Ostrinia nubilalis

为了解球孢白僵菌对玉米螟的致病机理,本研究应用扫描电子显微镜和透射电子显微镜技术,观察了球孢白僵菌sfzz003对玉米螟的侵染过程及其超微结构变化。结果表明,接种后24 h,分生孢子已萌发,并以芽管或菌丝的形式穿透体壁,普遍侵染。接种后48 h,穿透菌丝在虫体内大量繁殖,穿透过程中,菌丝与表皮层片层结构平行或垂直生长,也可侧向出芽。表皮层及皮细胞层因穿透而发生形变,菌丝周围出现组织溶解现象,这是机械压力与酶的联合作用。穿透菌丝周围可见白色絮状物,有的部位表皮层与皮细胞层分离,细胞器溶解。侵入血腔的菌丝以出芽的方式大量繁殖,至腔内充满菌丝。接种后72 h,菌丝已在寄主体表形成大量网状结构。球孢白僵菌发育进入晚期,虫体内大部分形成孢子,少量形成菌丝,可见由于营养耗尽而凋亡的菌体。本研究为更好地了解昆虫病原真菌与寄主的关系提供了理论基础,对应用白僵菌进行生物防治具有重要意义。

In order to understand the pathogenesis of B. bassiana to O. nubilalis,we observed the ultrastructural changes of B. bassiana sfzz003 infecting O. nubilalisusing scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The observation indicated that,at 24 hours after inoculation,the conidia are already germinated and penetrated the body wall in the form of germ tube or hypha. The infection was widespread. At 48 hours after inoculation,the hypha multiplyed in the body of insect. During the penetration,the hyphae were observed to grow parallel or perpendicularly in the cuticle,and they could also sprout laterally. It could be seen that the cuticle and the epidermis were deformed due to penetration,and histolysiscould be observed around the hypha,which was a combination of mechanical pressure and enzymatic action. Flocculent solutes appeared around the penetrant hypha. In some areas,cuticle was separated from epidermis,and organelles were dissolved. The hyphae that invaded the haemocoel massively proliferated by budding,and occupied the haemocoel. At 72 hours after inoculation,hyphea had formed a large number of reticular structures on the surface of the host. B. bassianadeveloped into the late stage. Most of them formed conidia,a small amount formed hyphae. We could also see apoptotic bacteria due to nutrient depletion. This study provides a theoretical basis for a better understanding of the relationship between entomopathogenic fungi and hosts,and is of great significance for the application of B. bassiana in biological control.