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RESEARCH ARTICLE (Open Access)
Contents Vol 72(6)

Understanding Rhododendron intraspecific compatibility in botanic garden collections for species conservation

Ling Hu https://orcid.org/0000-0003-2576-2143 A * , Susan E. Gardiner B , Jennifer A. Tate A C and Marion B. MacKay A
+ Author Affiliations
- Author Affiliations

A School of Agriculture and Environment, Massey University, Palmerston North 4442, New Zealand.

B The New Zealand Institute for Plant and Food Research Limited, Fitzherbert Science Centre, Palmerston North 4472, New Zealand.

C School of Food Technology and Natural Sciences, Massey University, Palmerston North 4442, New Zealand.

* Correspondence to: Gloria_hu95@outlook.com, l.hu1@massey.ac.nz

Handling Editor: Rachael Nolan

Australian Journal of Botany 72, BT24005 https://doi.org/10.1071/BT24005
Submitted: 11 January 2024  Accepted: 30 August 2024  Published: 19 September 2024

© 2024 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Context

Controlled pollination is an important technique for maintaining intraspecific diversity in integrated plant conservation practices, particularly in genera such as Rhododendron, where open pollination usually produces hybrids with unknown paternal lineages.

Aims

This study investigated the capacity for viable seed set from self- and intraspecific cross-pollination for Rhododendron taxa in different categories of the International Union for Conservation of Nature (IUCN) Red List, to guide conservation management of threatened species in botanic garden collections.

Methods

The following five taxa of subsection Maddenia were studied: R. dalhousiae var. dalhousiae (Least Concern), R. dalhousiae var. rhabdotum (Vulnerable), R. lindleyi (Least Concern), R. nuttallii (Near Threatened), and R. excellens (Vulnerable). Controlled pollination was performed on selected garden accessions, and seed germination was tested at an alternating temperature regime of 15/25°C, 8 h photoperiod, and ~6 μmol m−2 s−1 photosynthetic photon flux density (PPFD).

Key results

Intraspecific compatibilities varied among different taxa and between self- and outcross treatments. X-ray images for Rhododendron seeds showed low capacity to predict seed germination. Neither X-ray scan nor fungicide (Ridomil) treatment showed any adverse impact on seed germination, which has positive implications for seed-banking and subsequent raising of Rhododendron seedlings.

Conclusions

Controlled intraspecific pollination can be used to maintain diversity of ex situ accessions for selected Rhododendron species. However, the zero or low compatibility demonstrated in some species, such as R. excellens, suggests that these species may require a different approach.

Implications

Intraspecific pollination should be evaluated for each Rhododendron species before a propagation program is initiated in ex situ conservation.

Keywords: biodiversity conservation, botanic garden, controlled pollination, ex situ collection, germplasm, intraspecific compatibility, Rhododendron, seed germination, subsection Maddenia.

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