Genetic characterization of a spontaneous green-type pigmentation mutant of Porphyra yezoensis and the significance of using heterozygous conchocelis in nori farming

In order to characterize the spontaneous green-type pigmentation mutant of Porphyra yezoensis, growth and contents of photosynthetic pigments were compared with those of the wild type in gametophytic blades. The growth of the green mutant was slower than that of the wild type. The content of phycoerythrin was markedly lower in the green mutant than in the wild type. For genetic analysis, the green mutant was crossed with the wild type. In the cross, the heterozygous conchocelis (the wild-type color) produced many sectored F-1 gametophytic blades, which were composed of both parental colors. The segregation ratio by counting the wild-type sectors and the green-type sectors of the F-1 blades was approximately 1 : 1. This suggests that the green mutant is governed by a single recessive gene. All the monospore germlings from the sectored F-1 gametophytic blades that originated from the heterozygous conchocelis developed into single-colored blades with either the green color or the wild-type color. The advantages of using heterozygous conchocelis (hybrid conchocelis) and monospores from F-1 gametophytic blades that originated from the heterozygous conchocelis in commercial farming of Porphyra yezoensis are detailed and discussed.