3.4 Evident local adaptation detected in the early-season WR populations
Evident local adaptation (LA) in the early-season WR populations was detected in the native early rice-cultivation environment (Table 2), based on the method recommended by Hereford (2009). For example, the average level of LA was 0.15 for plant height and 0.14 for reproductive traits. Generally, the positive values of LA indicate local adaptation for traits, but the early flowering was regarded as an adaptive trait in this study. Therefore, the negative value of -0.04 also indicated local adaptation for flowering time in the early-season WR populations. However, no such evident local adaptation was detected in the late-season WR populations in the native late rice-cultivation season (Table S7). These results indicated that ecological environment such as temperature and daylength played an important role in local adaptation of weedy rice (Figure 7).
In addition, the LA for plant height was stronger in population CDE (e.g., 0.32) and DCE (e.g., 0.21) than that in HJE (e.g., 0.14), as well as flowering time (Table 2). This result suggested more pronounced local adaptation of the early-season WR populations in CDE/L and DCE/L population pairs, likely associated with population histories of WR infesting cultivated rice field at different periods of times. Furthermore, the evident local adaptation for the number of seeds per plant and seed setting ratio were detected in all early-season WR populations, and it indicated that the local adaptation in the early rice-cultivation season may be conducive to the reproductive traits of the early-season WR populations.