AOBPreview published online on November 3, 2009
Annals of Botany, doi:10.1093/aob/mcp267
Asymmetric hybridization in Rhododendron agastum: a hybrid taxon comprising mainly F1s in Yunnan, China
1 Key Laboratory of Biodiversity and Biogeography, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650204, China
2 Institute of Molecular Plant Sciences, University of Edinburgh, Edinburgh EH9 3JH, UK
3 Royal Botanic Garden, 20a Inverleith Row, Edinburgh EH3 5LR, UK
* For correspondence. E-mail hsun{at}mail.kib.ac.cn
Received: 29 October 2008 Returned for revision: 21 April 2009 Accepted: 15 September 2009
Background and Aims: Rhododendron (Ericaceae) is a large woody genus in which hybridization is thought to play an important role in evolution and speciation, particularly in the Sino-Himalaya region where many interfertile species often occur sympatrically. Rhododendron agastum, a putative hybrid species, occurs in China, western Yunnan Province, in mixed populations with R. irroratum and R. delavayi.
Methods: Material of these taxa from two sites 400 km apart (ZhuJianYuan, ZJY and HuaDianBa, HDB) was examined using cpDNA and internal transcribed spacer (ITS) sequences, and amplified fragment length polymorphism (AFLP) loci, to test the possibility that R. agastum was in fact a hybrid between two of the other species. Chloroplast trnL-F and trnS-trnG sequences together distinguished R. irroratum, R. delavayi and some material of R. decorum, which is also considered a putative parent of R. agastum.
Key Results: All 14 R. agastum plants from the HDB site had the delavayi cpDNA haplotype, whereas at the ZJY site 17 R. agastum plants had this haplotype and four had the R. irroratum haplotype. R. irroratum and R. delavayi are distinguished by five unequivocal point mutations in their ITS sequences; every R. agastum accession had an additive pattern (double peaks) at each of these sites. Data from AFLP loci were acquired for between ten and 21 plants of each taxon from each site, and were analysed using a Bayesian approach implemented by the program NewHybrids. The program confirmed the identity of all accessions of R. delavayi, and all R. irroratum except one, which was probably a backcross. All R. agastum from HDB and 19 of 21 from ZJY were classified as F1 hybrids; the other two could not be assigned a class.
Conclusions: Rhododendron agastum represents populations of hybrids between R. irroratum and R. delavayi, which comprise mostly or only F1s, at the two sites examined. The sites differ in that at HDB there was no detected variation in cpDNA type or hybrid class, whereas at ZJY there was variation in both.
Key words: F1-dominated hybrid zone, species barrier, habitat disturbance, Rhododendron agastum, R. irroratum, R. delavayi