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GENETIC EVIDENCE FOR ZYGOTIC MEIOSIS IN PHYTOPHTHORA CAPSICI
Author(s) -
Timmer L. W.,
Castro J.,
Erwin D. C.,
Belser W. L.,
Zentmyer G. A.
Publication year - 1970
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1970.tb09926.x
Subject(s) - biology , offspring , auxotrophy , genetics , meiosis , heterothallic , phytophthora capsici , zygote , mating type , botany , gene , phytophthora , mutant , pregnancy , embryogenesis
Variation of several traits among single‐oospore isolates of the heterothallic oomycete, Phytophthora capsici , was studied to determine genetically the place of meiosis in the life cycle. Low percentages of met – offspring were recovered from two crosses of met – X prototrophic isolates. Arg – cultures were also recovered from the crosses indicating the possible presence of a suppressed arg – gene in one of the parental cultures. Three arg – X met – crosses yielded all four of the possible classes of offspring. Thus meiosis was either zygotic or, if gametangial, the original parental cultures must have been heterozygous at both the arg and met loci. However, when these parental cultures were crossed, only prototrophic offspring were recovered. A ratio of 3 prototrophs: 1 met – was obtained from cross R in which two prototrophic offspring from a previous arg – X met – cross were mated. This indicated the presence of a suppressor of met – and may explain the low recovery of met – offspring from earlier crosses. From backcrosses of met – offspring from this cross to the A 2 prototrophic parent, ratios close to the expected 1:1 were obtained. When the A 1 prototrophic parent of cross R (K‐10) was crossed to an A 2 prototrophic isolate, met – offspring were again recovered, which indicated that K‐10 carried a suppressed met deficiency. In two crosses of streptomycin‐resistant ( S r ) X sensitive ( S s ) isolates, ratio of 108 S s : 14 S r and 84 S s :14 S r were obtained. Although 1:1 ratios would have been expected if meiosis were zygotic, segregation of S s and S r in the F 1 generation indicated that gametangial meiosis was unlikely. Segregation of the A 1 and A 2 mating types in all crosses also indicated that meiosis was zygotic in P. capsici . Possible control of mating type by a single pair of alleles, by plasmids, and by more complex mechanisms is discussed in relation to the mating type ratios obtained.