Morphogenesis of powdery midew fungi in water

体外寄生白粉菌产生除吸器外寄主植物表面的所有营养器官和生殖器官。在文献中，关于水分对白粉菌生长的影响，有相互矛盾的证据。例如，一些研究人员报告了水对这些真菌的有害影响，如分生孢子破裂或次生菌丝破坏。相比之下，一些研究人员成功地将白粉菌分生孢子悬浮液接种在水中。然而，所有后者的研究人员都只使用水作为孢子悬浮液的中间成分，因此在水产生有害影响之前，接种后通过从叶表面蒸发，水可能很快就消失了。因此，还没有关于水分对白粉菌从孢子萌发到产孢子分化过程的影响的报道。在本研究中，如果白粉菌在水中培养而不油炸，水对白粉菌的活力没有影响，该真菌在培养120h后最终形成分生孢子。此外，据报道，接种大麦胚芽鞘后浸泡在水中也不会影响E.pisi的活力。然而，浸泡的E.pisi形成异常细长的生殖管的频率高于未浸泡的E.pisi。分生孢子在空气中孵化时，60%以上的芽管从分生孢子的下部萌发出来，而分生孢子在水中孵化时，萌发管的萌发位置是随机的。此外，小麦赤霉菌在空气条件下以较高的频率形成短萌发管，并试图穿透大麦胚芽鞘细胞，而在水条件下，它们的形成频率要低得多，即使形成了它们的胚芽管，它们的萌发率也很低。

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