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The genus Actinidia includes widely-sold kiwifruit, and is thus horticulturally important. We investigated the distribution, ploidy levels, and fruit characteristics of the natural populations of three edible Actinidia species [Actinidia arguta (Siebold & Zucc.) Planch. ex Miq., Actinidia kolomikta (Maxim. & Rupr.) Maxim., and Actinidia polygama (Siebold & Zucc.) Planch. ex Maxim.] in Hokkaido, the northern island of Japan. Actinidia arguta and A. kolomikta were common, and their habitat ranges overlapped. Actinidia polygama was less common, and its habitat was mostly limited to lowland deciduous forests. Flow cytometric analysis revealed that all wild collections of A. kolomikta and A. polygama were diploid, and that A. arguta was tetraploid, suggesting a lack of intraspecific ploidy variation. Fruit shape varied from round to ovoid in A. arguta, ranged from ovoid to ellipsoidal in A. kolomikta, and was ellipsoidal in A. polygama. The fruit skin of all species was glabrous, and skin color was orange in A. polygama, green to dark green in A. kolomikta, and light to dark green in A. arguta. The fresh weight of A. kolomikta fruit was less than that of A. arguta, and the soluble solids content (SSC) of the fruits varied widely within species. One sample of A. arguta had extremely high SSC (average Brix of 30.8%). The ascorbic acid content (AAC) was the highest in A. kolomikta (up to 805 mg per 100 g fresh weight). Actinidia arguta and A. kolomikta germplasm may be useful for breeding new kiwifruit varieties for cultivation in cold-temperate regions.

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