Many single spore gray wild type cultures ofThielaviopsis basicolaconsistently produce an average of 3.5ndash;4.2 albino sectors after 5ndash;10 days growth at 73deg;ensp;plusmn;ensp;3deg; F. on potato dextrose agar and other media. Sectoring was greatly reduced at fluctuating room temperatures of 76deg;ndash;87deg; F. and on certain media. Mass spore transfers from the albino sectors yield albino colonies with a small pigmented area around the center of transfer. Single spore cultures of the albino sectors inevitably revert to the gray parent. In contrast to the gray, brown type cultures rarely produce albino sectors or patches and these yield pure albino colonies that have remained stable for four years. All albino colonies are identical morphologically to the parents except in loss of pigment and a retarded thickening of the chlamydospore walls.The expression of albinism in gray type cultures cannot be explained on the basis of a simple gene mutation. Also, an explanation based on a variable phenotypic change, originating in the cytoplasmic enzyme system controlling pigmentation and under constant genotypic control, is not entirely adequate. The expression of albinism in brown type cultures has the characteristics of a gene-type mutation.
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