Physiologic specialization and genetics of the smut fungi. II

Holton, C. S.

doi:10.1007/bf02861825

Cited by 13 publications

(5 citation statements)

References 15 publications

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“…Dimixis occurs in all heteromictic Phycomycetes, Ascomycetes and Uredinales. It may also be tbe prevalent system in the Ustilaginales, but the situation needs further investigation and at present the number of loci and mating-type factors involved is in dispute (Whitehouse, 1951b;Holton, 1952;Rowell, 1954;Rowell and de Vay, 1954).…”

Section: Dimictic Systemsmentioning

confidence: 99%

The Mating Systems of Fungi I

Burnett

1956

New Phytologist

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Section: Dimictic Systemsmentioning

confidence: 99%

The Mating Systems of Fungi I

Burnett

1956

New Phytologist

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“…Numerous genetic investigations with Ustilago maydis have been mainly concerned with the isolation and description of mutants and with heterothallism. Apart from Perkins ' (1949) work on the production of biochemical mutants, large numbers of mutations affecting the morphology or colour of sporidial colonies have been examined (see Stakman, 1936;Christensen & Rodenhiser, 1940;Holton, 1953). A 2:2 segregation in tetrads for factors affecting colony appearance or mutability has occasionally been obtained (e.g.…”

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confidence: 99%

“…More recent studies by Rowell & De Vay (1954) and Rowell (1955a) showed that the production of brandspores in the host is controlled by alleles at two loci. Homothallic or solopathogenic strains, which appear as a result of irregular brandspore germination in certain crosses, have been frequently encountered (see Christensen & Rodenhiser, 1940;Holton, 1953). Induced segregation of mating-type factors from one such strain has been reported by Rowell (19556).…”

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The genetics ofUstilago maydis

1961

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1. Many of the Ustilaginales, or smut fungi, appear to have the qualities necessary for the application of modern techniques of microbial genetics.Ustilago maydisis considered the most suitable species.2. Investigations of the mating system confirm reports that the production of diploid brandspores in the host is controlled by alleles at two loci.3. Genetic markers were obtained by inducing mutations in a wild-type strain with ultra-violet light. Of 100 biochemical mutants which were isolated, the growth requirements of 94 were identified. Thirty of these were used in genetic tests.4. The compact growth of colonies on artificial media allowed new techniques to be developed by means of which large samples of progeny could be isolated and identified easily. The analysis of brandspore colonies consisting of the products of single meiotic divisions is the quickest method for detecting linkage, but its accurate measurement appears to be achieved by examining the individual members of tetrads.5. Linkage was detected relatively rarely, but eight markers, including theamating-type locus, were assigned to one or other of two linkage groups. Although recombination values were not always determined accurately owing to irregular basidiospore germination, the auxotrophic markers in each group could be mapped in a linear order. Since no indication of other linkage groups was obtained, the genetic evidence is so far consistent with cytological reports that the basic haploid chromosome number is two in the smut fungi.6. Three linked markers were used to investigate chromatid interference by tetrad analysis. None was detected in a total of eighteen double exchanges.

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“…Rowell & De Vay (1954) and Rowell (1955 a) showed that these processes were under the control of two loci, the a locus with two alleles and the b locus with multiple alleles. During the course of extensive investigations into the pathogenicity and mating system of U. maydis, several workers have encountered stable homothallic strains which were pathogenic when inoculated alone into the host (see Christensen & Rodenhiser, 1940;Holton, 1953). These strains appeared to be formed following the failure of reduction at meiosis during the germination of the brandspores.…”

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Induced mitotic crossing-over inUstilago maydis

Holliday

1961

Genet. Res.

147

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1. Two different methods of selection were used to obtain stable prototrophic solopathogenic strains ofUstilago maydisfrom haploids with different biochemical requirements. The strains were shown to be heterozygous diploids.2. Two diploids which were examined in detail had four markers in common, but they were in different coupling and repulsion phases. Rare spontaneous segregation was detected in one of the diploids, but a high frequency of segregation was obtained in both after treatment with ultra-violet light. The proportion of segregants amongst the survivors increased with the dose. These auxotrophic segregants were detected by means of the replica plating technique.3. The types of segregant which were obtained from both diploids were consistent with the view that they arose as a result of mitotic crossing-over. After low doses of radiation the reciprocal products of crossing-over were often detected. There was no evidence from the phenotypes of the segregants that haploidization was occurring. The diploidy of a sample of the segregants was confirmed by mating-type tests, and by the fact that they showed further segregation after another dose of radiation.4. A slow-growing unstable segregant recovered after a high dose of radiation proved to be a monosomic strain which consistently reverted to a stable diploid homozygous for one chromosome. It was possible to use this auxotrophic diploid together with a haploid with different biochemical requirements, to synthesize a prototrophic triploid strain. The triploid was much less stable than the diploid strains.5. By means of pathogenicity tests with certain segregants it was possible to distinguish the function of the two loci which control the mating system. Thealocus is responsible for the fusion of haploid sporidia and has no effect on the pathogenicity of the heterokaryon which is under the control of theblocus.6. The effects of ultra-violet light on mitotic crossing-over do not seem to be easily compatible with a copy choice or similar mechanism of recombination.

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Physiologic specialization and genetics of the smut fungi. II

Cited by 13 publications

References 15 publications

The Mating Systems of Fungi I

The Mating Systems of Fungi I

The genetics ofUstilago maydis

Induced mitotic crossing-over inUstilago maydis

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