Despite extensive studies on cultivated rice, the genetic structure and subdivision of this crop remain unclear at both global
and local scales. Using 84 nuclear simple sequence repeat markers, we genotyped a panel of 153 global rice cultivars covering
all previously recognized groups and 826 cultivars representing the diversity of Chinese rice germplasm. On the basis of modelbased
grouping, neighbour-joining tree and principal coordinate analysis, we confirmed the widely accepted five major groups of
rice cultivars (indica, aus, aromatic, temperate japonica and tropical japonica), and demonstrated that rayada rice was unique
in genealogy and should be treated as a new (the sixth) major group of rice germplasm. With reference to the global
classification of rice cultivars, we identified three major groups (indica, temperate japonica and tropical japonica) in Chinese
rice germplasm and showed that Chinese temperate japonica contained higher diversity than that of global samples, whereas
Chinese indica and tropical japonica maintained slightly lower diversity than that present in the global samples. Particularly,
we observed that all seasonal, drought-tolerant and endosperm types occurred within each of three major groups of Chinese
cultivars, which does not support previous claims that seasonal differentiation exists in Indica and drought-tolerant
differentiation is present in Japonica. It is most likely that differentiation of cultivar types arose multiple times stemming
from artificial selection for adaptation to local environments.