Nuclear selection in oidium formation from dikaryotic mycelia ofFlammulina velutipes

Abstract

The effect of nuclear dominance in monokaryotic oidium formation from dikaryotic mycelia in a tetrapolar basidiomycete,Flammulina velutipes, was examined. A total of 46 monokaryotic stocks were used to produce 194 hybrid dikaryotic stocks by crossing. The proportion of homokaryons among the oidium isolates from dikaryotic mycelia was over 95%. The staining of nuclei of oidia with propidium iodide showed that over 90% of oidia were monokaryotic and suggested that these oidia had single haploid nuclei at the G1 stage. The monokaryotic oidium isolates from hybrid dikaryons were backrossed to parental monokaryotic stocks. Although most of the monokaryotic oidium isolates (except for those from 17 hybrid dikaryons from a total of 194 test stocks) showed nuclear types similar to only one of the parental stocks, the process seems to produce essentially the split nuclear type composition. Therefore, the monokaryotization in oidium formation from dikaryotic mycelia essentially involves the process of nuclear selection. The two separate results of hierarchies of relative dominance among two nuclei of the parental dikaryons in the monokaryotic oidium formation by grouping with incompatibility factor compositions were determined. Only a few discrepancies were found in the hierarchies between the two specific nuclear compositions of hybrid dikaryons.