Genetic relationships based on SSR polymorphism in wild and ancient cultivated tea trees (Camellia sinensis L.) from China and India

Abstract

Tea is the most consumed non-alcoholic beverage in the world. China and India are the biggest tea producing countries and accounted for 58% of the global tea production in 2016. These two countries are also vital as domestication centres of tea. Ancient tea germplasm with over 1500 years old tea trees represents the most valuable tea germplasm resource in the world. Related wild species also represent vital gene pools for further genetic improvement. Yet, comprehensive studies on the population structure, genetic relationships among wild and ancient tree tea types lacking. Therefore, in the current study, we used 211 accessions including 78 wild tea plants representing 17 species (12 close wild relatives and 5 distantly related wild species) genotyped with 23 SSRs to investigate the genetic diversity, relationships and wild species contributed to the domestication of cultivated tea. SSR allelic polymorphisms revealed highest expected heterozygosity/genetic diversity (He=0.812) and private allele percentages (74.3%) in wild teas. Lowest expected heterozygosity (He=0.686) and second highest private allele percentage (13.3%) was reported in Chinese Assam tea (CAS). Conservation of related wild species and private allele rich CSA is of great importance. PCoA analysis revealed 4 distinct non-overlapping groups. Similarly NJ tree and Structure analysis also reported similar results. This indicates that cultivated tea possibly represent three independent domestication events in China and India. Yet, multiple analysis revealed that Chinese Assam type (CSA) and Indian Assam type tea (CSAIN) were more genetically similar than China type tea (CT). Close wild relative Camellia taliensis was found to be possibly contributed to the domestication of CSA in Yunnan, China. Chinese Assam tea was found to be not cultivating in India. Additionally, Indian tea germplasm reported being having a limited gene pool. Therefore, we recommend incorporating wild teas and CSA into the tea breeding programmes in India.