Genetic variation and population demography of the landrace population of Camellia sinensis in Kasuga, Gifu Prefecture, Japan

Abstract

Tea, Camellia sinensis, is economically, medicinally and culturally a very important crop. Most of the tea gardens in Japan contain clonally propagated cultivars; however, landraces that were propagated by seed contain valuable genetic variations, providing important resources for future tea breeding. Genetic diversity and differentiation, as well as the population demography of ten landrace populations in Kasuga, Gifu, Japan were investigated using microsatellite markers. All ten populations showed similar levels of genetic variation and there was no significant differentiation between them. These ten populations can be considered to represent a single large population. Gene flow between them may be natural or the result of artificial but random seed exchange by local farmers. The level of genetic diversity in the Kasuga population was compared with that in Kyoto and in China. Kasuga and Kyoto showed similar levels of genetic diversity and this suggests that the value of genetic resources in these two regions is about equal. The level of genetic diversity in Kasuga was much lower than that in China. A coalescent approach revealed that the Kasuga population suffered from severe population reduction (0.1 %) 965 years ago and then exponentially expanded to its current level. This timing and the strength of the bottleneck corresponds to the time when tea plants were brought to Japan from China by Buddhist priests in the ninth–twelfth century. Lower genetic diversities in Japanese populations are thus considered to be the result of the small number of founders brought from China.