2.1 Plant materials
A total of six WR populations occurring in the early (code as WRE) and late (WRL) rice-cultivation seasons were collected from three rice fields in Leizhou, Guangdong Province of China (Table S1). The geographic distance between the sampled rice fields were >30 km. WR populations collected from the same field were treated as a population pair (e.g., CDE/L, DCE/L or HJE/L pair). About 60 randomly selected samples were collected from each WR population of either the early- or late-season rice field at the spatial distance intervals of >10 m to avoid the sampling of similar genotypes. Matured panicles from a WR plant were collected as an independent sample. The average duration of the early rice-cultivation seasons (ES) was from March 1st to June 25th, whereas that of late rice-cultivation seasons (LS) was from July 20th to November 5th.