160 



PHYSIOLOGY OF THE FUNGI 



the pH range of many fungi to vary on different media and concluded 

 that the widest pH range was obtained on favorable media. 



The temperature of incubation may influence the optimum pH as well 

 as the pH range of a fungus. The optimum pH for Phacidium infestans 

 is 4.5 at 5°C., 5.0 at 10°C., 5.5 at 15°C. and 6.0 at 20°C. (Pehrson, 1948). 

 The pH range of Armillaria mellea on a sucrose-peptone medium was 

 reported to be 2.5 to 7.5 at 15°C., 2.0 to 7.8 at 25°C., and 2.5 to 7.4 at 

 35°C. (Wolpert, 1924). 



21 



180 



150 



.120 



■o 



.^ 90 



o 



60 



30 



90 



8.0 



7.0 



60 



5,0 



4.0 



3.0 



20 



25 



5 10 15 



Doys of incubation 



Fig. 24. Rate of mycelial growth of Sordaria fimicola and accompanying changes 

 in pH of two media. Media contained biotin but no thiamine. Sohd hnes indicate 

 growth, and the broken lines represent pH values. 



Two pH optima have been reported for a number of fungi. Rhizopus 

 nigricans, when grown on potato-glucose liquid medium, has two optimum 

 pH ranges, one on either side of the isoelectric point of the mycelium, 

 which was about pH 5.5 (Robbins, 1924). Scott (1924) reported 

 Fusarium lycopersici to have two optimum pH ranges for growth on 

 glucose-nitrate medium: pH 4.5 to 5.3 and 5.8 to 6.8. Mathur et al. 

 (1950) obtained evidence that there are two optimum pH ranges for the 

 sporulation of Colletotrichum Undemuthianuni. 



In addition to the use of media having low initial pH values, the lower 

 pH limit may be determined in some instances by choosing a medium 

 in which the fungus produces sufficient acid to inhibit growth completely. 

 This is illustrated by the pH and growth curves of Sordaria fimicola in 

 Fig. 24. This fungus was grown upon a glucose-ammonium sulfate 

 medium having initial pH 6.0; after a few days the pH of the culture 

 medium fell to 3.3 and remained there for 5 weeks. More difficulty may 

 be experienced in determining the upper pH limit. If a fungus is able 



