MORPHOGENESIS IN TRICHODERMA: AUTONOMOUS AND NONAUTONOMOUS PIGMENTATION IN HETEROKARYONS OF COLOR MUTANTS IN TRICHODERMA VIRIDE

The final step in the process of conidiation—conidial pigmentation—was studied in the fungus Trichoderma viride. Twenty-nine auxotrophic, color mutants, isolated from the same green wildtype strain, were paired to produce stable heterokaryons in all possible combinations and grouped according to their complementation behavior. No complementation (green pigmentation) was found in any of the heterokaryons formed by pairs of white (W) mutants. However, these mutants could be separated into two groups with respect to their behavior when paired with yellow (Y) and brown (Br) mutants. When W^c mutants were paired with any of the Y or Br mutants complementation took place. However, W^d mutants displayed this reaction with only one group of yellow mutants (Y^a) and not with the other (Y^b) nor with Br mutants. In noncomplementing heterokaryons such as Y^b/W^d, only yellow and white conidia were produced, pigmentation being autonomous. On the other hand, in heterokaryons in which complementation did take place, as for instance Y^a/W^d, green as well as white and yellow conidia were produced. Differential sensitivity to UV irradiation was used to show that the green conidia were of either W^d or F^a genotype, indicating a nonautonomous type of gene action. It is suggested that the genes W^c, Y^a, Y^b and Br have a sequential structural role in the biosynthesis of the green pigment, while W^d controls the activity of three (W^c, Y^b, Br) of these genes.