402 PHYSIOLOGY OF THE FUNGI 



mon. Industries involved in the commercial production of alcohols, 

 certain organic acids, and antibiotics are in constant search for higher 

 yielding "strains" of the species in present use, as well as of other species 

 of fungi. Such a search led to the discovery of PenicilHum chrijsogenum 

 Q176 and its variants, which are high producers of penicillin. Brewer's 

 yeast is said to grow in media with an alcohol content as high as 14 to 

 17 per cent, while the baker's yeast is checked in about 4 per cent alcohol 

 (Wolf and Wolf, 1947). Both yeasts belong to the species Saccharomyces 

 cerevisiae. 



A different type of variation, apparently linked with sexuality, is 

 reported in Mucor racemosus (Harris, 1948). Here, the production of an 

 undetermined antibiotic seems to be confined to the minus strain. Varia- 

 tion in bioluminescence is reported for Panus stypticus (Macrae, 1942). 

 The fruit bodies and mycelium of the strain found in North America 

 are luminescent, while those found in Europe are not (Fig. 77). Variants 

 of the same species commonly differ in pigment production (Christensen 

 and Graham, 1934; Leonian, 1929). Mutants, or saltants, are commonly 

 lighter in color than the parent type. 



Sporulating ability. Many investigators have noted the spontaneous 

 development of nonsporulating cultures or sectors from a sporulating 

 mycelium. Variation in abundance of spores produced by different 

 isolates from nature is also common. For example, some of the species 

 which illustrate this variability are Fusarium spp., Phytophthora spp., 

 Phoma terrestris, Gibber ella zeae, Glomerella cingulata, Lenzites trabea, 

 Monilinia fructicola, and Ustilago striiformis. Variations in fruit bodies 

 of Cyathus stercoreus produced in culture are described by Brodie (1948). 

 Variation in production of sclerotia has been observed in isolates of 

 Sclerotinia trifoliorum by Kreitlow (1949) and of S. sclerotiorum in our 

 laboratory. 



Pathogenicity. Variability in the metabolic products such as enzymes 

 and toxins and in the ability to establish compatible food relations with 

 the host may be of great importance in determining pathogenicity. Das 

 Gupta (1936) discusses the pathogenicity as well as other characteristics 

 of "saltants." Such soil-inhabiting fungi as Fusarium spp. are notorious 

 for their variability in pathogenicity within a species. Species of Helmin- 

 thosporium (Christensen, 1922; Dickinson, 1932) and Cortidum solani 

 (Houston, 1945) are likewise highly variable. In the highly parasitic 

 fungi, such as the smuts, rusts, and powdery mildews, there is a high 

 degree of physiologic specialization of races. 



The determination of physiologic races is based on infection types of 

 several varieties or species of the host. Dickson (1947) reports the 

 existance of 189 known physiologic races of Puccinia graminis tritici and 

 128 physiologic races of P. rubigo-vera tritici. Genetic studies indicate 



