BackgroundTea is the world’s most popular non-alcoholic beverage. China and India are known to be the largest tea producing countries and recognized as the centers for the domestication of the tea plant (Camellia sinensis (L.) O. Kuntze). However, molecular studies on the origin, domestication and relationships of the main teas, China type, Assam type and Cambod type are lacking.Methodology/Principal FindingsTwenty-three nuclear microsatellite markers were used to investigate the genetic diversity, relatedness, and domestication history of cultivated tea in both China and India. Based on a total of 392 samples, high levels of genetic diversity were observed for all tea types in both countries. The cultivars clustered into three distinct genetic groups (i.e. China tea, Chinese Assam tea and Indian Assam tea) based on STRUCTURE, PCoA and UPGMA analyses with significant pairwise genetic differentiation, corresponding well with their geographical distribution. A high proportion (30%) of the studied tea samples were shown to possess genetic admixtures of different tea types suggesting a hybrid origin for these samples, including the Cambod type.ConclusionsWe demonstrate that Chinese Assam tea is a distinct genetic lineage from Indian Assam tea, and that China tea sampled from India was likely introduced from China directly. Our results further indicate that China type tea, Chinese Assam type tea and Indian Assam type tea are likely the result of three independent domestication events from three separate regions across China and India. Our findings have important implications for the conservation of genetic stocks, as well as future breeding programs.

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Citrus canker (Xanthomonas axonopodis pv. citri) has brought great damage to citrus industry worldwide, and it is difficult to control, so the use of resistant genotypes seems the only choice. All the tested citrus species showed typical symptoms when artificial inoculation was performed. The present study aimed to find genotypes possessing active resistance to canker disease. A total of 14 accessions from three species were investigated by puncture inoculation of excised leaves with the pathogen, and it was found that ÔHuaihuaÕ, ÔSanyeÕ and ÔNo.25-86Õ in Citrus ichangenesis, ÔShenjuÕ and ÔZhenchengÕ in C. junos had fewer disease spots on pin-holes with delayed symptom appearance; while ÔChinese CitronÕ (C. medica) did not show any lesions. These six genotypes were further tested in an epidemic field by inoculation with 2.5 · 10 7 cfu/ml of pathogen solution for 2 years. Only the tested citron showed complete and active resistance, with tissue necrosis on the pin-holes; the other five accessions were all infected with different disease incidences. Therefore, the citron accession was considered as a resistant genotype, and was already used for resistant cultivar breeding.

A Tea is the most popular non-alcoholic beverage in the world. Asia accounts for 85% of the global tea production. Comprehensive studies on the genetic diversity and origin of domestication of tea plant are scarce, while the studies carried out to date also used fewer number of markers narrowing down its scope. Genotyping by Sequensing (GBS) is a novel next generation sequensing technique which generates large amounts of Single Nucleotide Polymorphysms (SNPs) that are vital for modern genetic analysis. Therefore, 114 wild, landraces and cultivated tea samples collected across 14 countries in Asia were subjected to GBS analysis to study the genetic relationships and origin of domestication of tea plant in Asia. A set of 247,760 high quality SNPs were generated and used for the genetic analysis of 112 samples. Multiple analysis with SNPs revealed three independent domestication events for cultivated tea confirming the results of simple sequence repeat analysis. Most of the wild species clustered together while few species/samples clustered differently showing their gene flow with the cultivated tea or possible hybrid origins. Structure and neighbour joining tree analysis clearly showed a differential clustering of Assam tea collected from India, Sri Lanka and other South Asian countries with the Assam tea collected from China and neighbouring countries in East Asia. Future studies with the recently published tea genome possibly identify differentially selected genes/biochemical pathways during tea domestication. Based on the findings of this most comprehensive study done on tea plant to date, incorporation of Chinese Assam tea germplasm into the breeding programmes in India, Sri Lanka and other South Asian countries is recommended.

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