Natural interploidy hybridization among the key taxa involved in the origin of horticultural chrysanthemums

Shuai Qi,Long‐Zhen Wang,Nian Wang,Alex D Twyford,Jun‐Yi Ding,James S Borrell,Yue‐Ping Ma

doi:10.1111/jse.12810

Abstract

AbstractUnderstanding hybridization and introgression between natural plant populations can give important insights into the origins of cultivated species. Recent studies suggest differences in ploidy might not create such strong reproductive barriers as once thought, and thus studies into cultivated origins should examine all co‐occurring taxa, including those with contrasting ploidy levels. Here, we characterized hybridization between Chrysanthemum indicum L., Chrysanthemum vestitum (Hemsley) Ling and Chrysanthemum vestitum var. latifolium (Zhou & Chen), the most important wild species involved in the origins of cultivated chrysanthemums. We analyzed the population structure of 317 Chrysanthemum accessions based on 13 microsatellite markers and sequenced chloroplast trnL‐trnF for a subset of 103 Chrysanthemum accessions. We identified three distinct genetic clusters, corresponding to the three taxa. We detected 20 hybrids between species of different ploidy levels, of which 19 were between C. indicum (4x) and C. vestitum (6x) and one was between C. indicum and C. vestitum var. latifolium (6x). Fourteen hybrids between C. indicum and C. vestitum were from one of the five study sites. Chrysanthemum vestitum and C. vestitum var. latifolium share only one chloroplast haplotype. The substantially different number of hybrids between hybridizing species was likely due to different levels of reproductive isolation coupled with environmental selection against hybrids. In addition, human activities could play a role in the different patterns of hybridization among populations.

Highlights

Hybridization has played an important role in plant domestication and diversification through human history (Heslop‐Harrison & Schwarzacher, 2007; Arnold, 2014; Cornille et al, 2014)
The number of alleles scored in Chrysanthemum vestitum and C. vestitum var. latifolium was significantly higher than Chrysanthemum indicum at eight and seven loci, respectively (P < 0.05); this was expected for a hexaploid possessing more chromosome copies than a tetraploid species (Fig. S1)
Most hybrids identified by the STRUCTURE analysis fell between C. indicum and C. vestitum in the principal coordinate (PCO) plot (Fig. 2)

Summary

Introduction

Hybridization has played an important role in plant domestication and diversification through human history (Heslop‐Harrison & Schwarzacher, 2007; Arnold, 2014; Cornille et al, 2014). Multiple important crops have been generated through hybridization either between wild species or through introgression from crop wild relatives into cultivated lineages. L.) (Simmonds & Shepherd, 1955; Heslop‐Harrison & Schwarzacher, 2007), and ornamental species such as tree peonies (Paeonia suffruticosa Andrews) (Zhou et al, 2014), cherry (Prunus yedoensis Matsumura) (Baek et al, 2018), and dahlia (Dahlia variabilis L.) (Saar et al, 2003). Hybridization occurs more between species of the same ploidy level than differing ploidy levels.

Methods

Results

Conclusion