Karyotype And Hybid Origin Of Rosa Draelucens Byhouwer Based On FISH

Rosa praelucens Byhouwer is one of the famous alpine ornamental flowers endemic to Yunnan.It is also an important rose germplasm resources tolerant to coldness.Moreover,R.praelucens is the only decaploid wild rose species which has the highest chromosome number once reported.However,the hybrid origination of this species is yet unclear.Furthermore,there exists rich phenotypic variation within the species,the cytological and molecular basis of which is also unknown.In order to identify the possible original ancestors of R.praelucens,and to explore if there exists any variation in chromosomal number and chromosomal structure within the species,the cytological Fluorescence in situ Hybridization(FISH)with 45S rDNA and 5S rDNA as probes was used to study the karyotypes of R.praelucens and 20 other closely related and sympatrically distributed cogeneric species.At the same time,the 45S rDNA and 5S rDNA were physically mapped in the mitotic metaphase chromosomes of 10 individual R.praelucens plants with different phenotypes.The results were as follows:(1)FISH with 45S rDNA and 5S rDNA as probes could identify some of the chromosomes more accuratately and improve the results of karylogical study of genus Rosa,Among the studied 21 rose species,only the karyotype of R.praelucens was 2B,and that of the other 20 species all belonged to 2A.(2)Some 45S rDNA loci in 14 species,namely,R.graciliflora,R.omeiensis var.omeiensis,R.sericea,R.mairei,R.sertata,R.davidii,R.banksiopsis,R.persetosa,R.macrophylla,R.acicularis,R.moyesii,R.odorata var.pseudoindica,R.roxburghii and R.praelucens were fragile site.The number of 45S rDNA hybridization sites in 20 rose species was the same as their ploidy in the interphase,except for the diploid R.banksiopsis,which had three 45S rDNA hybridization sites in the interphase.Although some hybridization sites were fractured,the number of 45S rDNA sites equaled to its ploidy level.(3)The number and location of 5S rDNA loci was uncertain.The observed number of 5S rDNA loci might increase if the chromosomes were incompletely concentrated during the interpahse and metaphase.Diploid R.willmottiae var.glandulifera,R.odorata var.pseudoindica,R.helenae,R.brunonii and R.soulieana var.soulieana all had four 5S rDNA hybridization sites in both interphase and metaphase.In addition,there were four 5S rDNA hybridization sites in the interphase of diploids R.davidii and R.banksiopsisis,but only two 5S rDNA hybridization sites could be observed in the metaphase.The 5S rDNA hybridization loci of other 14 species in both interphase and metaphase were identical with their ploidy level.(4)Based on the mapping of rDNA in the chromosomes of R.praelucen.s and its 20 relative species,together with the results of molecular data reported before,it could be postulated that R.graciliflora,R.moyesii and R.murielae were the original ancestors of R.praelucens.Due to the lack of molecular proofs,R.sikangensis could not be removed from the list of possible ancestors.(5)There existed some variation in chromosomal number and chromosomal structure among different individuals within R.praelucens.Except for decaploid individuals with 70 chromosomes,there were tetrasomic enneaploid individuals with 65 chromosomes(2n=9x+2=65)and enneaploid ones(2n=9x=63).As far as chromosomal structure were concerned,as there existed much difference in 45S rDNA loci within the species,some individulas might have undergone large site deletion or gene copy reduction.