1887

Abstract

All the single-spore cultures originating from zoospores and oospores of wild-types of were sensitive to chloramphenicol and streptomycin. Cultures from zoospores and oospores of chloramphenicol-resistant mutants were resistant to chloramphenicol but not streptomycin, while those from zoospores and oospores of streptomycin-resistant mutants were resistant to streptomycin but not chloramphenicol. When chloramphenicol-resistant A (6133C) of was paired directly with streptomycin-resistant A (6134S) of the same species, all single-oospore cultures from three crosses were resistant to either chloramphenicol or streptomycin but not both, suggesting absence of genetic exchange in the progeny. Appearance of A resistant to chloramphenicol and A resistant to streptomycin was due to a mating-type change during oospore formation because oospores produced by A through hormone stimulation also gave rise to A cultures, and vice versa. Similar results were obtained when reciprocal crosses involving the same direct and membrane-separated pairings between streptomycin-resistant A and chloramphenicol-resistant A were studied. When A wild-type (6133), sensitive to both chloramphenicol and streptomycin, was paired with A double mutant 6134CS, resistant to chloramphenicol first and streptomycin later, all single-oospore cultures from three crosses were either sensitive to both chloramphenicol and streptomycin or resistant to both antibiotics, indicating that all single-oospore cultures from direct pairing were of uniparental origin. When A isolate 6134S, resistant to streptomycin, was paired directly with its A variant 6134VC, resistant to chloramphenicol, all single-oospore cultures from three crosses were resistant to either chloramphenicol or streptomycin but not both, indicating an apparent absence of genetic exchange in the progeny. This ruled out the possibility that absence of genetic exchange in the crosses between two different isolates of might be due to genetic divergence between the strains crossed. We interpret the results of this study to show that all progenies from direct pairings between different mating types of were of uniparental origin, although close linkage or mitochondrial location of the markers cannot as yet be eliminated as possible explanations of the apparent absence of genetic exchange. We propose the term hormonal heterothallism to denote this suggested novel phenomenon.

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/content/journal/micro/10.1099/00221287-134-11-2985
1988-11-01
2022-01-22
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