New insights into the hybrid origin of Malus toringoides and its close relatives based on a single‐copy nuclear gene SbeI and three chloroplast fragments

摘要: Abstract MalustoringoidesHughesanditscloserelatives,M.maerkangensisM.H.Chengetal.,M.setokVassilcz.,and M. xiaojinensis H. Cheng & N. G. Jiang were supposed to derive from hybridizations. However, moleculardataarestillinadequatetocorroboratethehybridoriginhypotheses.Inthisstudy,wesequencedasingle‐copynucleargene SbeI and three chloroplast fragments carried out phylogenetic analyses investigate the evolutionaryoriginsoftheabovefourputativehybridtaxa.ThehybridnatureofM.toringoidesisconfirmedbythedetectionoftwodistincttypesofSbeIsequencesfromit.ThechloroplastandSbeIgenephylogeniesshowthatthematernalprogenitorof toringoides is closely related sikkimensis P. Balakr. spectabilis Borkh., paternalprogenitoris mostlikely M.transitoriaC. K.Schneid.Thehypothesisthat M.kansuensis(Batalin)C. K.Schneid.isoneoftheparentsofM.toringoidesisnotsupported.MalusmaerkangensisandM.xiaojinensismighthaveoriginatedthrough hybridization between kansuensis, whereas setok genetically toM.toringoides.ThethreecloserelativesofM.toringoidesweredesignatedasthreenovelspeciesbysomeresearchers,however, as they all apomictic with limited distribution areas originated andpolyploidization, we recommend that their species status should be re‐evaluated.Key words close relatives, hybrid origin, hybridization, Malus toringoides, single‐copy nuclear gene.Hybridization polyploidization have beensuggested play an important role in evolutionand speciation genus Mill. (Robinsonet al., 2001; Potter et 2007). It was estimated that46% taxa are polyploids (Vamosi D Talent, 2009). Malustoringoides Hughes, a series Kansuensesof (Robinson 2001), has beenfound multiple ploidy levels (2x, 3x, 4x)and highly variable leaf shapes (Yu 1974). Themorphology of leaf, flower, fruit indicates thatM. might derived hybridizationbetween transitoria C. K. Schneid. andM. kansuensis (Batalin) (Cheng al.,1999; Deng 2002). In addition, additivepolymorphisms internal transcribed spacer(ITS) sequences observed few accessions ofM. further supported hypothesis ofhybrid origin (Feng 2007).Several other show morphological similaritytoM. toringoidesand wouldhavebeen derivedfromit.ThefirstisM.maerkangensisM.H.Chengetal.,whichonly occurs Maerkang Heishui (SichuanProvince, China) shows intermediate morphologyof 1992b; 2002).The second Vassilcz., distributedalongtheLancangRiverBasinoftheTibetanplateauaswell western Sichuan Province, which hasintermediate characters betweenM. 2002;Deng The third H.Cheng Jiang, reported severallocations (Xiaojin, Maerkang, Lixian) westernSichuan Province 1983, 2000). Malusxiaojinensis morphologically kansuensisand its karyotype extremely similar (Liang Li, 1993). Geographically,M. transitoria, andthe recently described (M. maerkangensis,M. setok, xiaojinensis) sympatric