The Journal of General and Applied Microbiology
Online ISSN : 1349-8037
Print ISSN : 0022-1260
ISSN-L : 0022-1260
HEREDITARY VARIATION AND GENETIC RECOMBINATION IN KOJI-MOLDS (ASPERGILLUS ORYZAE AND ASP. SOJAE)
VI. GENETIC RECOMBINATION IN HETEROZYGOUS DIPLOIDS
CHIYOKO ISHITANIYONOSUKE IKEDAKIN-ICHIRO SAKAGUCHI
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1956 Volume 2 Issue 4 Pages 401-430

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Abstract

1. The artificial production of new stable heterozygous diploid strains was carried out by using mutants of Asp. Sojae with color and nutritional markers.
2. These new strains were obtained through the formation of heterocaryons in the following combinations: y leu+al his, y arg+al his, and y arg +al leu.
3. The frequency of the spontaneous occurrence of diploid strains differs according to the combinations of the component strains (0.2-3.0G per 106 plated conidia).
4. The frequency of the occurrence of the diploids was raised to 2-9 per 102 surviving conidia by UV irradiation-this was an increase of>104 times.
5. The properties of the heterozygous diploids are as follows:
a) Conidial heads were uniformly green like the original wild type, while all heterocaryons had, in varying proportions, mixtures of white, yellow, and green conidial chains.
b) Growth on M.M. was like that of heterocaryons but unlike either component strain. On C.M., or a synthetic medium supplemented with either or both of the growth factors required by the component strains, they exhibited mostly homogenous green colonies, instead of segregating out into yellow and albino sectors like the heterocaryon.
c) They were exceedingly stable and 99.5 per cent of the colonies remained green. After 10-14 days' incubation, they rarely produced spots or sectors of either component color. The majority of the heterocaryons segregated into the two component strains, however, and only about 15 per cent remained heterocaryotic.
d) Genetic analysis of the diploids showed the following results. As for the color markers, 0.1-0.5 per cent of yellow or albino segregants occurred. Among these, yellow segregants further gave albinos in low ratio (0.1-0.3 per cent). Concerning the nutritional marker, the diploids were prototrophic and yellow or albino segregants were either prototrophic or required the same substances as the component strains. However, in the combination y arg+al leu, three new segregants have been obtained which differ from the component strains.
e) The diploids and their segregants were nearly the same as the original wild type and the component strains in the diameter of their conidia.
f) Heterozygous diploids and their segregants had on the average about one half as many nuclei as the original wild type or the component strains.
g) The DNA content per conidium was nearly the same as the original wild type and the component strain, but the DNA content per nucleus was about twice as large.
h) The new efficient method developed for the production of new strains of asexual fungi promises much in the way of the strain improvement required by industry.

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