Asymmetric protoplast fusions between wild species and breeding lines of potato – effect of recipients and genome stability

 The objective of this study was to investigate if in asymmetric protoplast fusion experiments the ploidy of the recipient line (di-haploid and tetraploid) has an influence on the extent of the asymmetry of the regenerating fusion products. Nineteen different experiments with the wild species Solanum bulbocastanum and Solanum circaeifolium as donors (irradiated with 210 Gy) and different breeding lines (di-haploid and tetraploid) were carried out. The degree of genome elimination was determined by measuring the relative DNA content using flow cytometry. The data showed that the loss of DNA in hybrid plants was significantly higher for 4x, compared to 2x, plants as recipients. In addition, the stability of asymmetry in the fusion products was studied. For this purpose differences in asymmetry in individual shoots originating from the same callus were analysed. A large variation in the DNA content of individual shoots was detected. Of the 4x to 6x shoots 44% had the same DNA content as another shoot originating from the same callus, 19% had a DNA content between 4x and 6x but different from any other analysed shoot originating from the same callus, 2% were chimeras and 35% had a completely different DNA content (eutetraploid, euhexaploid, eupolyploid or asymmetric with a ploidy level above 6x). RFLP-analysis with single-copy probes of 12 regenerates from six calli (two regenerates per callus) confirmed the assumption that the different regenerates of one callus originate from the same single cell. The analysis of selected regenerates cultivated for a period of more than 1 year demonstrated that the genome of asymmetric regenerates might change during cultivation. Received: 30 April 1998 / Accepted: 24 July 1998