Genetic Diversity and Origin of Weedy Rice in Central Region of Jiangsu Pro- vince, China

Genetic divergence of weedy rice populations associated with their geographic location and coexisting conspecific crop: Implications on adaptive evolution of agricultural weeds

“…Noticeably, genetic diversity of Jiangsu weedy rice populations was nearly 10‐fold greater than that from the other two regions in northeastern and southern China. The increased genetic diversity of weedy rice populations in Jiangsu province is most likely attributed to the multiple origins or diverse sources of weedy rice individuals within the populations, similar to that reported by Shao et al () using SSR markers, in which approximately 60% of genetic variation presented within weedy rice populations. We consider that the change of rice varieties in this region promoted the differentiation of weedy rice because the traditionally grown indica rice varieties have been gradually replaced by japonica varieties in Jiangsu province for the past 10 years (Zhong et al, ; Zhang et al, ; Shao et al, ).…”

“…The increased genetic diversity of weedy rice populations in Jiangsu province is most likely attributed to the multiple origins or diverse sources of weedy rice individuals within the populations, similar to that reported by Shao et al () using SSR markers, in which approximately 60% of genetic variation presented within weedy rice populations. We consider that the change of rice varieties in this region promoted the differentiation of weedy rice because the traditionally grown indica rice varieties have been gradually replaced by japonica varieties in Jiangsu province for the past 10 years (Zhong et al, ; Zhang et al, ; Shao et al, ). The reduced weed control due to limited human labor input may also increase the within‐population genetic diversity of weedy rice, as reported by Cao et al () and He et al () in which the authors reported substantially reduced genetic diversity of weedy rice by manual removal of weedy rice plants.…”

“…Our results indicated a relatively high level of overall genetic diversity for weedy rice populations based on InDel fingerprints. The level of overall genetic diversity was comparable with that determined using microsatellite (simple sequence repeat, SSR) markers for weedy rice populations from China or other regions (Cao et al, ; Zhang et al, ; Shao et al, ; Xia et al, ; Jiang et al, ). However, genetic diversity for each of the weedy rice populations is much lower than the overall value, particularly for populations from northeastern China and Guangdong province, although the number of weedy rice samples from each population was comparable with other studies (Cao et al, ; Xia et al, ; Jiang et al, ).…”

“…Commonly, genetic analysis based on InDel markers often suggests the strong genetic differentiation of weedy rice into two extreme types, either indica or japonica , with extremely low numbers of intermediate types (e.g., Liu et al, ; Zhang et al, ). Apparently, the gradual change of rice cultivation from indica to japonica varieties in Jiangsu province in recent years has played a significant role in shaping the genetic composition of weedy rice into indica , japonica , and intermediate types at the same locations, probably by seed‐mediated gene flow and allelic introgression, as suggested in other studies (e.g., Chen et al, ; Shao et al, ; Xia et al, ; He et al, ).…”

“…Obviously, the change in rice varieties from indica to japonica has gradually increased the sources of weedy rice, leading to the current pattern of genetic diversity and divergence in Jiangsu rice fields. The newly formed endo‐feral ( japonica ) type of weedy individuals could have mixed with those emerged from the indica type of weedy seeds maintained in the soil seed‐banks, and consequently formed the complex composition of weedy rice populations in Jiangsu (see also Shao et al, ). A similar situation of the complex origin of weedy rice was also found in Sri Lankan rice fields, where the relatively high level of genetic diversity within weedy rice populations was created by seed‐mediated gene flow along with the long‐distance seed exchange of rice cultivars by farmers (He et al, ).…”