CIPC-Induced and Spontaneously Produced Diploid Myxamoebae in a Myxomycete, Didymium Iridis: A Study of Mating-Type Heterozygotes

SUMMARY

Isopropyl N-(3-chlorophenyl) carbamate (CIPC) is a commonly used herbicide which disrupts microtubule organization in plants. Because of this, CIPC and other mitotic inhibitors have been used extensively to create polyploid lines. This report is the first one on the use of CIPC to create polyploid clones in a myxomycete. These clones are particularly useful for studying apogamic development and the effects of myxamoebal mating-type heterozygosity. Two haploid myxamoebal clones of Didymium iridis carrying different mating types (A⁷ and A⁸), but identical recessive plasmodial-color alleles (b²) were diploidized by treatment with CIPC and crossed to produce a 4N, cream-colored Plasmodium (wild-type is brown). Six of 23 F₁ myxamoebal progeny from this plasmodium did not form plasmodia in single-spore culture, whereas the remaining 17 did. The 17 diploid apogamic, plasmodium-forming clones were heterozygous for mating-type (A⁷A⁸), and all produced the expected cream-colored plasmodia. Five of the F₁ mating-type heterozygotes were crossed with CR 2–25, a 2N mating-type homozygote (A⁵A⁵), which carries wild-type color alleles (b²⁺b²⁺). In three of the five crosses, both brown and cream-colored plasmodia developed in the same plate. The 4N, brown-colored plasmodia were the result of mating between the two clones, whereas the 2N, cream-colored plasmodia developed apogamically. Both cream and brown-color alleles were recovered in the F₂ progeny derived from the 4N, brown-colored plasmodium.