3G8 PHYSIOLOGY OF THE FUNGI 



LONGEVITY OF SPORES 



The length of Hfe of spores is usually measured by their ability to 

 germinate after various periods of time. It is affected by environmental 

 conditions, principally temperature and moisture. The greatest period 

 of longevity reported for fungus spores appears to be among the Myx- 

 omycetes. Smith (1929) succeeded in germinating spores from herbarium 

 specimens of Myxomycetes 5 to 32 years after they were collected. A 

 few of the common species whose spores germinated after approximately 

 30 years are Physarum cinereum, Fuligo septica, Hemiirichia clavata, and 

 Stemonitis ferruginea. Smut spores also have a long period of viability 

 (Lowther, 1950). Spores of Aspergillus orijzae germinated after 22 years 

 in a sealed tube at room temperature (McCrea, 1923). 



In contrast to long periods of longevity, some fungus spores die very 

 soon after they are liberated. The sporidia of Cronartium rihicola lived 

 less than 10 min. at room temperature with a humidity of 90 per cent 

 (Spaulding, cited by Doran, 1922). Sporidia of Gymno sporangium 

 juniperi-virginianae lived no longer than 6 days in dry air. Eight weeks 

 is reported as the maximum longevity of aeciospores of C. rihicola, with 

 only 5 per cent germination after 7 weeks. In general, aeciospores of the 

 rust fungi remain viable about 50 per cent longer than the urediospores, 

 whose average longevity ranged from 30 to 60 days (Doran, 1922). 



Other factors have been reported to influence longevity of spores. 

 Ascospores of Endothia parasitica remained viable for a year when dried 

 in the bark, but when removed from the bark, they lost the ability to 

 germinate within 5 months (Anderson and Rankin, 1914). Similarly, 

 conidia in dry spore horns retained viability for at least a year, but when 

 placed in water, separated, and then dried, the time was less than 1 

 month. It seems likely that one of the functions of the gelatinous matrix 

 of the conidia of certain fungi, such as Gloeosporium, Colletotrichum, and 

 Cytospora, is to increase the longevity of the spores through its water- 

 holding capacity. 



Light is apparently only of minor importance as a factor influencing 

 longevity. No doubt ultraviolet light in nature plays an important part 

 in reducing the period of viability and even in killing many of the hyaline 

 spores. Spores having dark walls are protected somewhat against the 

 penetration of the ultraviolet rays. 



SUMMARY 



Spore germination represents a change from an inactive to an active 

 phase in the life cycle of a fungus. Since it involves the first stages of 

 growth, it is reasonable to expect that many of the factors which influence 

 vegetative growth also affect spore germination. On the other hand, 

 the spore, being a resting cell, may contain stored materials not usually 



