Development of Apogamic Amoebae From Heterothallic Lines of a Myxomycete, Didymium Iridis

By making appropriate crosses between heterothallic sexual clones of Didymium iridis we can recover apogamic lines in the F1 generation. In this organism, heterothallic forms typically produce a haploid myxamoebal stage, but recently two diploid myxamoebal clones homozygous for mating types were discovered. When these are crossed, A2A2 x A5A5, tetraploid Plasmodia are produced which later yield diploid F1 meiospores. Sixty‐four percent of the single‐spore‐derived clones produce both myxamoebae and Plasmodia, while the remainder do not progress past the myxamoebal stage. These results are consistent with the predictions that from tetraploid nuclei, mating types should segregate in the meiospores in a ratio of 1A2A2:4A2A5:1A5A5, and that myxamoebae heterozygous, A2A5, for mating type should yield Plasmodia apogamously. As the means for verifying relative ploidy levels of myxamoebae and Plasmodia, nuclear DNA was measured with a scanning microspectrophotometer.