Morphogenesis of powdery midew fungi in water

外寄生白粉病真菌在其寄主植物表面产生除吸器外的所有营养和生殖器官。关于水分对白粉病菌生长的影响，文献中存在着相互矛盾的证据。例如，一些研究人员报告了水对这些真菌的有害影响，如分生孢子的破裂或次生菌丝的破坏。与此相反，一些研究人员成功地接种草与白粉病分生孢子悬浮液在水中。然而，所有后来的研究人员都采用水作为孢子悬浮液的培养基成分，因此，在接种后水产生有害影响（如果有的话）之前，水通过从叶片表面蒸发而很快消失是合理的。因此，没有关于水分对白粉病菌孢子萌发到产孢分化过程的影响的报道。研究结果表明，不经油炸而直接在水中培养的小麦白粉病菌，其生活力不受水的影响，培养120 h后即可形成分生孢子。此外，据报道，豌豆肠球菌接种到大麦胚芽鞘后浸入水中也不影响其生活力。然而，浸泡的豌豆真囊线虫以更高的频率形成异常伸长的芽管。这一现象的原因是：孢子萌发部位受分生孢子所处环境条件的影响，在空气中培养时，60%以上的孢子萌发于赤道型分生孢子的下部，而在水中培养时，孢子萌发部位是随机的。此外，在空气条件下，小麦赤霉病菌的短芽管形成频率较高，并试图穿透大麦胚芽鞘细胞，而在水分条件下，其形成频率较低，即使形成芽管，

Ectoparasitic powdery mildew fungi produce all vegetative and reproductive organs except haustoria on the surface of their host plants. In the literatures there are contradictory evidences concerning the effects of water on growth of powdery mildew fungi. For example, some researchers reported harmful effects of water on these fungi, such as bursting of conidia or damage of secondary hyphae. In contrast, some researchers successfully inoculated grasses with powdery mildew conidial suspensions in water. However, all of the latter researchers adopted water just for medium ingredient for spore suspension, and thus it is plausible that the water disappears soon by evaporating from the surface of leaves after inoculation before the water gives harmful effects, if any. Thus, no report is available concerning the effects of water on the differentiation process from spore germination to sporulation of powdery mildew fungi. In this stude, it is shown that water has no effect on the viability of Erysiphe graminis if ther are incubated in water without being fried, and the fungus eventually formed conidia 120 h after the onset of incubation. Moreover, it is reported that the viability of E.pisi is also unaffected by immersing in water after inoculation to barley coleoptile. However, immersed E.pisi formed abnormally elongated germ tubes at higher frequency that of unimmersed ones. This phenomenon was explained as follows ; the emerging sites of germ tubes were affected by environment conditions to which conidia had been exposed ; if the conidia were incubated in air, more than 60% of germ tubes emerged from lower sites of conidium equater, while the emerging sites of germ tubes were at random when the conidia had been incubatedin water. Moreover, short germ tubes of E.graminis were formed at high frequency and they tried to penetrate barley coleoptile cells in air condition, while their formation frequency in water condition was much lower, and even if they were formed, their