CHAPTER 18 



PHYSIOLOGICAL VARIATIONS AND INHERITANCE OF 

 PHYSIOLOGICAL CHARACTERS 



Variation in the results of experimental work with fungi is of frequent 

 occurrence; it is perhaps even more frequent than uniformity. Different 

 investigators conducting the same experiments with the same species of 

 fungus have often failed to obtain the same results. Such variation may 

 be attributed to (1) genetic differences in the strains or isolates used, (2) 

 slight nutritional differences in the experiments, or (3) differences in the 

 physical environment. Examples of the second and third groups of 

 factors have been pointed out frequently in the earlier chapters. A brief 

 discussion of the genetic differences involving physiological expression 

 and the general mode of inheritance of these factors (in so far as they are 

 known) will be given. 



PHYSIOLOGICAL VARIATION 



Variation in physiological behavior of different species of fungi has 

 been noted in the preceding chapters. The present discussion emphasizes 

 the physiological variation within a species, i.e., between different isolates, 

 strains, or races, which show little or no morphological difference. 



Nutritional requirements. Variations in the nutritional requirements 

 of different isolates of the same species are numerous. Differences in 

 vitamin requirements or in carbon and nitrogen utilization may serve as 

 examples. 



Differences in deficiencies for one or more vitamins have been reported 

 for different isolates of Fusarium avenaceuni (Robbins and Ma, 1941), 

 Sclerotinia minor (Barnett and Lilly, 19-47), Saccharomyces cerevisiae 

 (Leonian and Lilly, 1942; Burkholder and Moyer, 1942), Sordaria fimicola 

 (Hawker, 1939; Barnett and Lilly, 1947a), and numerous others. For 

 example, certain isolates of Sordaria fimicola from nature are totally 

 deficient for biotin alone, while others are deficient for both biotin and 

 thiamine. A somewhat different type of variation is reported by Thren 

 (1941) for Ustilago nuda. The haploid mycelium showed no deficiency 

 for vitamins, while the diploid mycelium required an external supply of 

 thiamine or pyrimidine. The plus and minus strains were also found to 

 differ in their nutritional requirements. 



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