Preliminary Identification Of Natural Hybrids Between Chrysanthemum Indicum And Chrysanthemum Vestitum

Chrysanthemum indicum is widely distributed in northeast China,north China,central China,south China and southwest China,with pinnate or lobed leaves and yellow tongue-shaped flowers.Chrysanthemum vestitum was divided into two varieties: C.vestitum var.vestitum and C.vestitum var.latifolium based on leaf morphology and distribution.The C.vestitum var.vestitum has ovate-lanceolate leaves and is distributed in Yichang,Hubei province and the Funiu Mountains,Henan province whereas C.vestitum var.latifolium has ovoid leaves and is mainly distributed in Dabie Mountains and Tianzhu Mountains,Anhui province.There is a differing ploidy level between C.indicum and C.vestitum with the former reported as tetraploid and the latter reported as hexaploid.Within areas where C.indicum and C.vestitum co-occour,their flowering periods partially overlap despite that C.vestitum flowered slightly earlier than C.indicum.We observed some individuals with intermediate morphological characters between C.indicum and C.vestitum and these may represent putative hybrids between the two species.In this study,we genotyped 317 individuals using 13 SSRs,representing 75 C.vestitum var.latifolium,83 C.vestitum var.vestitum,134 C.indicum and 25 putative hybrids.We sequenced chloroplast trnL-trnF for a subset of individuals,including 22 C.vestitum var.latifolium,32 C.vestitum var.vestitum,42 C.indicum and 17 putative hybrids.We performed STRUCTURE and principal coordinate analysis?PCO?based on the 13 SSRs.We carried out haplotype analysis based on the trnL-trnF fragment.In addition,we performed morphometric analyses for a subset of individuals.The result of STRUCTURE and principal coordinate analysis?PCO?based on the 13 SSRs,identified three genetic clusters,corresponding to C.vestitum var.latifolium,C.vestitum var.vestitum and C.indicum.The results also showed that there were different degrees of revealed natural hybridization and gene introgression between C.indicum and C.vestitum.Most of the putative hybrids with intermediate morphological characters betweenC.indicum and C.vestitum were identified as hybridization or backcrossing between C.vestitum and C.indicum.Some individuals morphologically resembling C.indicum or C.vestitum were identified as hybrids based on STRUCTURE clustering analysis.The haplotype distribution map based on the trnL-trnF fragments showed that the haplotypes Hap₁ was shared by C.indicum and C.vestitum and most populations also have their own unique haplotypes.Suspected natural hybrids have no their unique haplotype.The principal component analysis?PCA?based on leaf morphology separated C.indicum,C.vestitum and C.vestitum var.latifolium with PC1 and PC2 explaining 51.24 % and 15.74 % of variation,respectively.In summary,frequent hybridization has occurred between C.indicum and C.vestitum,possibly due to the weak reproductive isolation between the tetraploids and the hexaploids.