Evaluation of Genetic Diversity in Wild Tachibana Population of Heda, Shizuoka, Using DNA Marker Analysis, and Stable Maintenance of the Population

Tachibana (Citrus tachibana (Makino) Tanaka) is a citrus species indigenous to Japan. It has been known since before the Nara period (~800 AD), and several wild populations are present in forests along the Pacific coast, from Tokai to Kyushu Island. Although tachibana was previously regarded as consisting of a single genotype, recent research with DNA markers suggested there are at least three different genotypes. Previous work was carried out across different wild populations, but little is known about the genetic diversity within each population, or among populations. In this study, wild tachibana trees of a population in Heda, Shizuoka (n = 64; 24 in Ida area and 40 in Kamiya area) were sampled to explore the population’s genetic diversity and promote utilization and conservation. Using DNA marker analysis for both nuclear and organelle genomes, we confirmed that, in total, 60 plants (22 in Ida and 38 in Kamiya) had a tachibana-A strain genotype. Four unidentified citrus plants in the sample were genotyped as Natsudaidai (C. natsudaidai Hayata). No selfed or hybrid offspring were found in either area. The observations suggest that it may be difficult to obtain hybrids from tachibana-A as seed parents, and another DNA marker analysis of open-pollinated seeds showed similar results. The survey revealed several young tachibana trees in the population, and we suggest that vegetative propagation by polyembryonic seeds may facilitate asexual maintenance of this tachibana population.