OBJECTIVETo acquire homozygous tetraploid germplasm of Rhodiola sachalinensis.

METHODPEG-mediated protoplast fusions were conducted using callus of Rh. sachalinensis as materials. Protoplast fusion products were embedded and cultured in low-density, low-melting-point agar and marked according to the protoplast size, and single-celled sister lines were established to acquire genetically homozygous tetraploid germplasm.

RESULTR(D) and R(M) of newborn daughter cells or protoplasm, metaphase cells or protoplasm were approximately in line with the formula R(D) = 0.793 7R(M). The change range in diameter of the diploid cells without fusion, two protoplasts fusion product were: 16.7 microm < or = R < 21.3 microm, 21.0 microm < or = R' < 26.8 microm respectively. There is an overlap between the two diameter ranges. The protoplast inoculation density of 1 x 10(4) cells x mL(-1) was appropriate when protoplasts were anchored by low-intensity, low-melting-point agar. Under the conditions of this density, plating efficiency was high and single cell origin of the sister lines microclones grew rapidly, and it was easy to mark the single cell microclones, and separate from each other to subculture. The chromosome counts results showed that chromosome numbers of diploid and tetraploid of single cell lines were 26 and 52, respectively. The result from flow cytometry assay showed that there is no presence of chimerism in single-cell regeneration plantlets.

CONCLUSIONThe results of this study provide a scientific basis for polyploid breeding of Rh. sachalinensis.