412 SPORE GERMINATION 



logical significance: in studies of temperature, the medium and its 

 container must be adjusted to the experimental temperature before 

 spores are sown. We may assume that this precaution has often been 

 overlooked and deduce that many temperature-germination curves are 

 in error, in that they exaggerate the extent of germination at sub- and 

 supraoptimal temperatures. 



As noted in Chapter 1, a given fungus usually has about the same 

 temperature response whether mycelial growth or spore germination is 

 the criterion (24, 86); a few exceptions have been reported (84, 298). 



10. OXYGEN AND GERMINATION 



It will be recalled that mycelial growth in fungi is often possible at 

 very low oxygen pressures but that truly anaerobic growth is unlikely 

 (Chapter 1). Virtually the same applies to spore germination in gen- 

 eral, with a few exceptions to be noted here. 



Failure of submerged spores to germinate or to germinate normally 

 has often been observed and credited, without proof, to oxygen deficit. 

 As pointed out by Gottlieb (113), too many other factors are affected 

 by submergence for this simple evidence to be aceptable. 



Ideally, experimental studies on the oxygen requirements for spore 

 germination should include, first, demonstration of the response to 

 graded oxygen pressures which are accurately measured and, second, 

 proof that the spores which fail to germinate at a given p0 2 are still 

 viable. Relatively few experiments meet this ideal standard. Uredo- 

 spores of Puccinia graminis tritici (2) and chlamydospores of Ustilago 

 zeae (217) fail to germinate at zero oxygen pressure and reach maxi- 

 mum or near-maximum germination at 30-38 mm of oxygen. Conidia 

 of Botrytis cinerea germinate as well in 5 per cent oxygen as in air (37), 

 but spores of Synchytrium endobioticum are severely inhibited at 3 

 per cent oxygen (292). 



Removal of oxygen by pyrogallol prevents germination in, for ex- 

 ample, uredospores of rust fungi (6, 129) and chlamydospores of Usti- 

 lago avenae (143). Although conidia of Erysiphe graminis are reported 

 to germinate at a low level in an atmosphere of nitrogen (70), other 

 studies on powdery mildew fungi indicate that germination is pre- 

 vented by anaerobiosis (34, 167). Ascospores of Neurospora tetra- 

 sperma also fail to germinate anaerobically (107). 



Conidiosporangia of three species of Phytophthora can germinate by 

 swarmspore formation — but not by germ tube — under anaerobiosis, 

 although other members of the Peronosporales fail completely to ger- 

 minate without oxygen (291). In the Mucorales, it appears that spores 



