Genetic analyses of ancient tea trees provide insights into the breeding history and dissemination of Chinese Assam tea(Camellia sinensis var.assamica)

Chinese Assam tea(Camellia sinensis var.assamica)is an important tea crop with a long history of cultivation in Yunnan,China.Despite its potential value as a genetic resource,its genetic diversity and domestication/breeding history remain unclear.To address this issue,we genotyped 469 ancient tea plant trees representing 26 C.sinensis var.assamica populations,plus two of its wild relatives(six and three populations of C.taliensis and C.crassicolumna,respectively)using 16 nuclear microsatellite loci.Results showed that Chinese Assam tea has a relatively high,but comparatively lower gene diversity(H_(S)=0.638)than the wild relative C.crassicolumna(H_S=0.658).Clustering in STRUCTURE indicated that Chinese Assam tea and its two wild relatives formed distinct genetic groups,with considerable interspecific introgression.The Chinese Assam tea accessions clustered into three gene pools,corresponding well with their geographic distribution.However,New Hybrids analysis indicated that 68.48%of ancient Chinese Assam tea plants from Xishuangbanna were genetic intermediates between the Puer and Lincang gene pools.In addition,10%of the ancient Chinese Assam tea individuals were found to be hybrids between Chinese Assam tea and C.taliensis.Our results suggest that Chinese Assam tea was domesticated separately in three gene pools(Puer,Lincang and Xishuangbanna)in the Mekong River valley and that the hybrids were subsequently selected during the domestication process.Although the domestication history of Chinese Assam tea in southwestern Yunnan remains complex,our results will help to identify valuable genetic resources that may be useful in future tea breeding programs.

Genetic analysis of walnut cultivars from southwest China:Implications for germplasm improvement

Walnuts are highly valued for their rich nutritional profile and wide medicinal applications.This demand has led to the intensification of breeding activities in major walnut production areas such as southwest China,in order to develop more superior cultivars.With the increasing number of cultivars,accurate identification becomes fundamental to selecting the right cultivar for grafting,industrial processing or development of new cultivars.To ensure proper identification of cultivars and understand the genetic structure of wild and cultivated material,we genotyped 362 cultivated and wild individuals of walnut trees from southwest China(with two additional populations from Xinjiang,plus three cultivars from Canada,France and Belgium) using 36 polymorphic microsatellite loci.We found relatively low indices of genetic diversity(H_(O)=0.570,H_(E)=0.404,N_(A)=2.345) as well as a high level of clonality(>85% of cultivars),indicating reliance on genetically narrow sources of parental material for breeding.Our STRUCTURE and PCoA analyses generally delineated the two species,though considerable levels of introgression were also evident.More significantly,we detected a distinct genetic group of cultivated Juglans sigillata,which mainly comprised individuals of the popular ’Yangbidapao’ landrace.Finally,a core set of 18 SSR loci was selected,which was capable of identifying 32 cultivars.In a nutshell,our results call for more utilization of genetically disparate material,including wild walnut trees,as parental sources to breed for more cultivars.The data reported herein will significantly contribute towards the genetic improvement and conservation of the walnut germplasm in southwest China.