SPORE LONGEVITY 



399 



Techniques of preservation of spores are briefly reviewed in Chap- 

 ter 1. 



Temperature is one of the major factors in the longevity of spores. 

 Almost without exception, survival is greatest at low temperature, i.e., 

 near 0°C. This is particularly well documented for uredospores of 

 rust fungi (57, 77, 214, 215, 237) and conidia of powdery mildew fungi 

 (317). Presumably, spore metabolism is accelerated at high tempera- 

 ture, reserves are exhausted, and death (inability to germinate) ensues. 

 The effect of subzero temperatures on survival is considered later 

 (Chapter 13). 



Relative humidity is the second major factor in spore longevity and, 

 in nature, is probably more often limiting than is temperature. Here, 

 however, the relation is not so simple, and we must for the present at 

 least distinguish three types of response to atmospheric moisture. Co- 

 nidia of Sphaerotheca pannosa (167), sporidia of rust fungi (222, 262), 

 and conidiosporangia of Phytophthora spp. (63, 141) survive longest at 

 saturation and are less viable at any relative humidity less than 100 per 

 cent. Typical data appear in Figure 4. It should be noted that pre- 

 cisely these spores have just been described as short-lived in general: 

 their susceptibility to desiccation is almost certainly the reason for their 

 failure to survive. 



Uredospores of the rust fungi exhibit a different and characteristic 

 response to humidity. Virtually all studies agree that survival is great- 



3 4 



Time, hours 



Figure 4. The survival of sporangia of Phytophthora iiif< .sinus at different relative 

 humidities. Redrawn from Crosier (03), by permission of the Cornell University 

 Agricultural Experiment Station. 



