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

摘要

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.