Possibility of polyploidy breeding using cryptic species in the marine crop <italic>Pyropia yezoensis</italic> (Bangiales, Rhodophyta).

In the marine crop <italic>Pyropia yezoensis</italic>, 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 <italic>P. yezoensis</italic> f. <italic>narawaensis</italic>. The F₁ 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 <italic>P. yezoensis</italic> and cryptic species were different species using the biological species concept. Almost all the archeospores that were released from the surviving F₁ blades developed into normal gametophytic blades. The result of nuclear DNA marker analysis revealed that the F₁ blades that developed from both conchospores and archeospores were allodiploids in the haploid gametophytic phase. Although their F₁ blades were extremely slender, their blade color was a deeper reddish brown as compared with that of <italic>P. yezoensis</italic> f. <italic>narawaensis</italic>, and the rate of blade length increase was remarkably higher in the blades of F₁ 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. [ABSTRACT FROM AUTHOR]