The isolation of haploid myxamoebal clones from a diploid apomictic isolate of the myxomycete Didymium iridis

Abstract

Clones of myxamoebae which fail to produce plasmodia have been isolated from cultures of the Philippine-1 isolate of D. iridis. These clones have been maintained continuously in the laboratory for a period of more than three years without producing plasmodia. It has been demonstrated by Feulgen-DNA cyto-photometry that the mean nuclear DNA content of such clones is equivalent to the haploid replicated (2C) value. Conversely, myxamoebal clones which produce plasmodia have an average nuclear DNA content which is equivalent to the diploid replicated (4C) value. These latter data are consistent with our earlier report that the Ph-1 isolate is apomictic (therrien, C.D. and J.J. Yemma 1974. American Journal of Botany 61:400-404). The haploid Ph-1 clones have been demonstrated to be cross compatible with clones bearing the mating alleles A1 and A3 through A11, and incompatible with clones bearing the mating allele A2. Furthermore, plasmodia which result from the Ph-1n x Pan 2-4 (A7) cross have a mean nuclear DNA content which is equivalent to the diploid replicated value. Such data demonstrate that the Ph-1n clones are sexually compatible with haploid amoebae of heterothallic isolates. The significance of the isolation of these haploid clones with regard to a recent hypothesis related tot he evolution of heterothallism in the Myxomycetes will be discussed.