What does this research mean for the field?

Natural hybridization between Hydrangea macrophylla and H. serrata occurs in many populations on the Boso and Izu Peninsulas, influenced by habitat topography. Novelty: ClaimNovelty.NOVEL_FINDING. Consensus alignment: ConsensusAlignment.NEUTRAL.

What question did this study set out to answer?

This research aims to assess the genetic conservation of Hydrangea macrophylla and evaluate its hybridization with H. serrata.

March 2, 2026The Horticulture Journal0 citationsOpen Access

Genetic Conservation of Endemic Hydrangea macrophylla: Assessing Natural Hybridization with H. serrata using ITS Sequences of Nuclear Ribosomal DNA

TUTatsuya UemachiUniversity of Shiga Prefecture NTNatsume TojoUniversity of Shiga Prefecture YHYuriko HayashiUniversity of Shiga Prefecture

Puntos clave

This research aims to assess the genetic conservation of Hydrangea macrophylla and evaluate its hybridization with H. serrata.
Analyzed the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA
Conducted phylogenetic analysis on 320 samples from various populations
Used PCR and direct sequencing to identify ITS sequence types
Identified 10 ITS types from H. macrophylla and H. serrata samples
Found minimal interspecific hybridization in the Izu Islands, but significant in the Boso and Izu Peninsulas
Suggested that habitat topography affects hybridization frequency among H. macrophylla populations

Resumen

Hydrangea macrophylla (Thunb.) Ser., an important genetic resource for the development of hydrangea cultivars, is endemic to a limited number of regions in Japan; however, there is a lack of comprehensive phytogeographical information essential for the conservation and effective utilization of this valuable genetic resource. In this study, we investigated the occurrence of natural hybridization between H. macrophylla and H. serrata within the distribution range of H. macrophylla by analyzing the internal transcribed spacer (ITS) regions of nuclear ribosomal DNA. Analysis of the H. macrophylla genome database revealed approximately 300 tandem repeats of ITS sequences in the genome. Two major ITS sequences, accounting for 55% to 59% of the total ITS sequences in the genome of H. macrophylla Aogashima-1 (the individual used for genome assembly), appeared to be inferable from electropherogram data obtained by direct sequencing of PCR products. From a total of 320 samples of H. macrophylla and H. serrata, 10 ITS types were identified. As a result of phylogenetic analysis, the ITS sequence types of H. macrophylla, H. serrata var. yesoensis, var. serrata, var. angustata, and some var. acuminata samples were grouped into a single cluster. Samples were collected from four of the Izu Islands, 16 populations on the Izu Peninsula, and 12 populations on the Boso Peninsula to estimate the occurrence of interspecific hybridization within the H. macrophylla distribution range. Direct sequencing results for PCR products of ITS sequences and morphological data showed that little interspecific hybridization had occurred in the Izu Islands; however, hybridization had occurred in many populations on the Boso and Izu Peninsulas. Furthermore, our findings suggest that habitat topography influences the frequency of interspecific hybridization among H. macrophylla populations. To conserve H. macrophylla genetic resources in the Boso and Izu Peninsulas, it is important to consider not only population decline, but also the impact of natural interspecific hybridization.

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