Possibility of polyploidy breeding using cryptic species in the marine crop Pyropia yezoensis (Bangiales, Rhodophyta)

In the marine crop Pyropia yezoensis , a cross-fertilization experiment between a cultivated strain and cryptic species was carried out to investigate the possibility of polyploidy breeding using cryptic species. To perform the cross-fertilization, we isolated a green mutant strain (IBYC-G1) of the cryptic species by heavy-ion beam irradiation. The green mutant was crossed with a wildtype strain (HG-4) of P. yezoensis f. narawaensis . The F 1 heterozygous conchocelis developed normally and released numerous conchospores. However, almost all the conchospore germlings did not survive past the four-cell stage or thereabout, and a few germlings developed into gametophytic blades. These results indicated that reproductive isolation occurred during meiosis and that P. yezoensis and cryptic species were different species using the biological species concept. Almost all the archeospores that were released from the surviving F 1 blades developed into normal gametophytic blades. The result of nuclear DNA marker analysis revealed that the F 1 blades that developed from both conchospores and archeospores were allodiploids in the haploid gametophytic phase. Although their F 1 blades were extremely slender, their blade color was a deeper reddish brown as compared with that of P. yezoensis f. narawaensis , and the rate of blade length increase was remarkably higher in the blades of F 1 than in those of the cryptic species. These results suggested that polyploidy breeding in the marine crop will attract more attention as a breeding method for further development of new cultivars.