5 Conclusions
Differences in temperature and daylength were found between early and late rice-cultivation seasons in Leizhou, with a lower temperature and longer daylength in the early seasons than those in the late seasons. These findings indicated that some stressful ecological elements, which can affect weedy rice growth and development, probably present in the early rice-cultivation seasons. In addition, significant differences in plant heights, the number of tillers per plant, flowering time, and reproductive traits were detected between the early- and late-season weedy rice populations occurring in the same rice fields in the early rice-cultivation season, and the early-season populations showed evident growth and development advantages than the corresponding late-season populations. Noticeably, such phenotypical divergence was associated with the local adaptation in the early-season weedy rice populations, suggesting that the adaptive evolution had taken place in weedy rice populations. Altogether, findings of this study provided solid evidence of phenotypic divergence between the sympatric early- and late-season weedy rice populations, likely associated with the local adaptation to their ambient temperature and photoperiod.