A Case of “Maternal” Inheritance in Neurospora Crassa

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Abstract
A slow-growth mutant, designated "poky," was observed among progeny of crosses of a standard wild type, 7A, to 4 different strains. Extensive studies of reciprocal crosses between poky and wild indicated that when poky was used as the protoperithecial parent only poky progeny resulted. When it was used as the fertilizing parent, the majority of the progeny had normal growth, although in each case there were a few spores with growth rates less than normal, but greater than those of poky. In making crosses it was important to time the cultures so that poky could be used as the protoperithecial parent. If the wild strain had a chance to form protoperithecia both wild and poky progeny were usually recovered. Since only poky progeny were obtained from crosses of poky x poky, it was unlikely that the wild progeny resulted from a reversion of poky. After several subcultures the wild type 7A behaved like a poky strain and is under observation. Growth of mixed cultures containing poky and a strain of not-poky, either of 2 arginineless mutants or a "colonial" double mutant was indistinguishable from that of controls, indicating that if the slow growth of poky were due to an infective agent, such as a virus, it was not readily transmissible by contact. A comparison of growth rates of poky and wild type at 25[degree]C in growth tubes of minimal medium indicated an avg. rate of 1.6 mm. per hr. for poky and 3.1 mm. per hr. for wild type. When dry wts. were compared, the growth rates for not-poky strains were about 8 times as high as those for poky strains. The growth rate of poky was not restored to normal to any supplement tested. Activities of certain enzymes were 0-40 percent higher in the poky strain than in the wild strain studied, but these differences, based on dry wt. of mycelium, were not considered significant. The poky and wild strains did not differ in polysaccharide content, but poky was relatively low in protein, nucleic acid and un-combined glucose in the few strains studied.

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