CHAPTER 14 

 FACTORS INFLUENCING SPORULATION OF FUNGI 



The life of the individual fungus is usually short and of uncertain dura- 

 tion. The continuance of the species (in most instances) depends upon 

 the production and dissemination of sexual or asexual spores. The 

 importance of spore production in the spread of epiphytotics is sufficient 

 reason to study the factors which control, modify, or inhibit this stage of 

 development in the life of the fungi. Some of the most difficult problems 

 which arise in the study of the life processes of the fungi are to be found 

 in the events and conditions which control the production of spores. 



In nature, we find many examples of the influence of certain environ- 

 mental and nutritional factors upon reproduction of the fungi. A num- 

 ber of parasitic fungi produce the perfect stage only in the spring, on or in 

 dead host tissue. This is true of Venturia inaequalis, Clavtceps purpurea, 

 Gnomonia ulmi, Monilinia jructicola, Coccomyces hiemalis, Guignardia 

 bidwelln, and others. Is the production of the sexual stage dependent 

 upon the pretreatment of cold, or freezing and thawing? Is it dependent 

 upon a favorable temperature and perhaps favorable intensity and dura- 

 tion of light? Or is it a matter of the proper nutrients which are made 

 available only after decay of the host tissues? These are difficult ques- 

 tions to answer, for it is likely that the production of the sexual stage 

 depends upon the proper balance of a number of factors. Similarly, we 

 may speculate about the stimuli involved in the formation of the peri- 

 thecia by the Erysiphales. Most of these obligate parasites form fruit 

 bodies late in the growing season. Perhaps, at least in some cases, this 

 is a reaction to cooler weather ; or perhaps the formation of perithecia is a 

 result of a decreasing or changing food supply as the host nears maturity. 

 Other physical factors are probably involved, since we know that the 

 abundance of perithecia varies from year to year. It is also of physio- 

 logical interest that many parasitic fungi produce conidia only while the 

 mycelium is actively attacking the living host. 



A critical investigation of the factors influencing reproduction requires 

 that the fungi be brought into the laboratory or greenhouse where external 

 factors can be controlled. Only one variable should be studied at a time, 

 and all other influencing factors must be controlled. It is, therefore, of 

 great advantage in physiological studies to be able to grow a fungus in 

 pure culture on synthetic or semisynthetic media. However, it n\ust be 



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