Abstract Detail

Floristics & Taxonomy

Hu, Ling [1], Tate, Jennifer [2], Gardiner, Susan [3], MacKay, Marion [1].

Ploidy variation in Rhododendron (Ericaceae) with a focus on the taxonomically complex subsection Maddenia.

Rhododendron is a ‘big genus’ of over 1300 taxa, where 1232 taxa have been Red List assessed and 730 placed in either a threat category or deemed Data Deficient. This sizable conservation problem is exacerbated by the taxonomic complexity inherent in a ‘big genus’. Rhododendron species encompass a range of life forms and niches and cover a geographic range from the Himalayas to SE Asia, where the center of Rhododendron diversity is found. In addition to the great species diversity, Rhododendron presents high ploidy diversity ranging from diploid (2x) to dodecaploid (12x).  Ploidy levels of species across the genus have been reported, but the extent of natural polyploidy has not been examined.   We reviewed ploidy data of Rhododendron taxa from previous research and summarized the taxonomic distribution of polyploids. Using subsection Maddenia (subgenus Rhododendron, section Rhododendron) as a case group consisting of both diploids and polyploids, the ploidy levels of different taxa were examined using flow cytometry together with verification of chromosome counts from flower buds of representative taxa. Our literature review revealed that polyploids are found more commonly in lepidote rhododendrons (subgenus Rhododendron). Section Rhododendron was the group with the highest frequency of polyploid taxa in the genus, regardless of the occasional discrepancy between data from flow cytometry and chromosome counts. Subsection Maddenia is an outstanding group with all diploid taxa, except for the R. maddenii complex, which consists of not only diploids (2x) but also different polyploids (4x, 6x, 8x, 12x). Our comprehensive sampling from ex situ living collections of newly identified 29 diploid taxa within subsection Maddenia and polyploids from pentaploid (5x) to octaploid (8x) in the R. maddenii complex. The outcome of using different dehydration methods for sample collection suggests a higher reliability for flow cytometry using silica dried leaves, rather than from herbarium specimens, when fresh leaves are unavailable. This study highlights the importance of further investigation on polyploidy in Rhododendron, as no ploidy data have been reported for the majority of species. As a group with multiple issues, including taxonomic complexity, ploidy variation, underestimated distribution and threatened taxa conservation, subsection Maddenia provides a model system for studying these matters. While the multiple ploidy levels in the R. maddenii complex may result from evolutionary progression, or an assembly of different polyploids from the synonymous species in this taxonomic complex, the underlying reason remains to be explained with the assistance of molecular phylogenetics.

1 - School of Agriculture and Environment, Private Bag 11-222, Massey University, Palmerston North, Manawatu-Wanganui, 4442, New Zealand
2 - Massey University, School of Natural Sciences, Massey University, Private Bag 11222, Palmerston North, Palmerston North, 4442, New Zealand
3 - The New Zealand Institute for Plant & Food Research Limited, Private Bag 11030, Manawatu Mail Centre, Palmerston North, Manawatu-Wanganui, 4442, New Zealand

subsection Maddenia
ploidy diversity
flow cytometry
Taxonomy .

Presentation Type: Oral Paper
Number: F&T II010
Abstract ID:280
Candidate for Awards:None

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