Germplasm Resources And Cytology Of The Genus Primula(Primulaceae) From China

Primula L.,comprising about 500 species,is the largest genus in the Primulaceae.Most species of the genus are restricted to the Northern Hemisphere,with a few extending to the Southern Hemisphere.Approximately 300 species have been recorded to occur in China for the genus,with the centre of modern diversification in the eastern Himalaya and the Hengduan Mountains region.The Chinese Primula has been generally well studied,particularly in its taxonomy,but the distribution pattern of its germplasm resources are not yet fully understood.Moreover,the overall variation pattern of chromosomal characters of the genus remains unknown due to the lack of cytological observations on many Chinese endemic species.The aims of this work were to(1)survey the germplasm resources of Primula in China based on extensive fieldwork,(2)assess their horticultural values,(3)investigate the conditions of ex situ cultivation of species,and(4)examine the cytological features of Chinese species as many as possible.The results are summarized as follows.1.During the fieldwork,a total of 368 populations representing 136 taxa(species,subspecies,and variety)in 20 sections were found.After a comparative analysis of the distribution data of the taxa,several conclusions have been reached:(1)In China Primula is mainly distributed in the Hengduan Mountains region(northwestern Yunnan and southwestern Sichuan)and the eastern Himalaya(southeastern Xizang).Most of the species are confined in narrow regions.The horizontal distributions are uneven between and within sections.(2)Vertically Primula is concentrated between 3100–4100 m a.s.l.,with most of the species at 3600 m a.s.l.(3)The habitats of the Primula species are extremely diverse,roughly falling into five types,i.e.shrubby type,marshy type,forest type,rocky type,and alpine type.The forest type seems to be most suitable for Primula species,and some widespread species can grow in various habitats.2.Among the 136 taxa collected in the wild,55 species have not been collected for 30 years,and three species(P.cavaleriei,P.tsiangii,and P.lithophila)have not been collected since the their first collection.(2)P.kwangtungensis is discovered in Hunan,representing a new record for this province.(3)Ten new species are described from a relatively narrow geographic range(i.e.23o–26o N,103o–113o E),including southeastern Yunnan,western Guizhou,southeastern Sichuan,southwestern Chongqing,southwestern Hunan,northwestern Guangxi,and northern Guangdong.This region is well characterized by Karst and Danxia landscapes,and the new species belong to sect.Carolinella,sect.Monocarpicae,and sect.Obconicolisteri.3.Fifteen species from sect.Proliferae and sect.Denticulataare are regarded as having high horticultural values.Thirty–three species from sect.Proliferae,sect.Muscariodies,and sect.Crystallophlomis are assessed to have moderate horticultural values.4.The germination of the seeds in the Chinese Primula is found to be affected by the treatments of temperature,light,and gibberellin.The temperatures most suitable for the germination of the seeds range from 20–25?,and the treatments of gibberellin and light are helpful to the germination.The seeds of five Primula species,including P.aurantiaca,P.denticulata,P.alpicola,P.chionantha,and P.vialii,are very sensitive to light.As to the ex situ cultivation,widely distributed species are generally much easier to cultivate,while alpine species are relatively difficult.Plants cultivated ex situ might grow actively,but with somewhat lower reproduction abilities.5.Fifty–one taxa(species and subspecies)in 13 sections of the Chinese Primula were cytologically studied.The chromosome numbers of 18 taxa are reported here for the first time.The base chromosome numbers(x = 8,9,10,11 and 12)suggested by previous studies are confirmed.The evolutionary pattern of the base chromosome numbers are further evaluated based on evidence from molecular phylogeny.The base chromosome numbers are homoplastic except for x = 12,although for some clades they are still of great systematic significance.The incidence of diploid taxa in the Chinese Primula is much more higher than that of polyploid taxa(ca.5 : 1),suggesting that the speciation of this genus from China may have had occurred mainly at the diploid level.However,polyploidization seems to be the main driving force of diversification in some clades,e.g.,sect.Auricula.Some species exhibit great intraspecific variation in ploidy level.The chromosomes are markedly variable in size among Primula species the significance of the intraspecific variation in ploidy level and the interspecific variation in chromosome size remains unclear,and further studies are needed.