HYPOBIOSIS IN FUNGI 1 1 3 



Cochrane-^, Garret- and Gottlieb^ do not see essential differences 

 between dormancy and maturation. If the resting period is 

 'relatively short', we speak of maturation; if it is, on the con- 

 trary, a matter of weeks or months, the spore is said to have a 

 dormant stage or resting period^. 



In some instances maturation seems to be associated with the 

 completion of cytological processes, while the subsequent 

 resting period involves physiological after-ripening. According 

 to Blackwell-^-^, oospores of Phytophtora cactorwn are unable to 

 germinate when they are first shed. Their nuclear fusion is 

 delayed until three to four weeks after shedding, a further 

 period of after-maturation lasting six to seven months follows 

 the nuclear fusion. This period of after-ripening can be reduced 

 by freezing, in contrast to the pre-fusion phase which is strongly 

 fixed. 



Spores that do not need after-ripening may fail to germinate 

 because of the presence of certain inhibitors liberated by the 

 spore-forming fungus. Rotem (personal communication) ob- 

 served that conidia of Alternaria solani do not germinate while 

 attached to the conidiophores, but germinate readily even when 

 artificially separated from the mycelium. Self-inhibition has 

 been reported for a number of fungi, such as Uromyces phaseoli^^, 

 Puccinia graminis tritici, Aspergillus niger, conidia of powdery 

 mildew fungi, and other spores listed by Cochrane^. Accroding 

 to Forsyth^^ uredospores of P. graminis tritici emit trimethyl- 

 ethylene which inhibits spore germination. Allen^^ determined 

 several properties of the substance presumably responsible for 

 the inhibhion of germination in uredospores of P. graminis 

 tritici. 



(b) Cryptobiosis in multicellular resting bodies 



Unlike spores consisting of one or a few cells, the resting 

 bodies discussed in the following are multicellular. Their biology 

 and survival ability are of paramount interest to the plant 

 pathologist. Some of the pathogenic fungi capable of forming 

 sclerotia, rhizomorph? or resting hyphae make disease control 



References p. 116 



