Genetic analysis on the incompatibility system ofAjellomyces dermatitidis

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Abstract
Analysis of mating types of numerous single ascospore isolates obtained from crosses between various strains of Arthroderma dermatitidis showed a 1:1 ratio of +vs - type. From this and the similar results from mating type tests, using 22 fresh clinical isolates, it was concluded that mating in A. dermatitidis is controlled by a bipolar incompatibility. Fruiting competence of the perfect state is found to be directly related to the formation of buff to yellowish-brown pigment in each strain and is independent of the mating factors. All the yellowish brown strains of single-ascospore isolates or fresh clinical isolates produced cleistothecia in single cultures that were devoid of ascospores (pseudocleistothecia). The majority of deep buff strains also produced such structures when paired with the same mating type, but fertile cleistothecia with the opposite mating type. White strains never produced pseudocleistothecia in single cultures and were sterile or poorly fertile when paired with the opposite mating type. Deterioration of the fruiting competence and pigment formation is extremely rapid in this species. Only 11% of strains maintained on agar slants more than 2 years produced fertile cleistothecia while 97% of fresh clinical isolates did so when paired with tester strains.