2.5 Estimate magnitude of local adaptation
Fitness related traits, such as plant height, number of tillers, and reproductive traits, were used to quantify local adaptation (LA) of native WR populations in different rice-cultivation environment. In addition, the flowering time was also involved in this analysis based on the data of days to flowering, and early flowering was regarded as an adaptive trait. The quantitative measure of local adaptation was the relative fitness of the native population at a field site in a given year minus the relative fitness of a nonnative population at that site, following the equation from (Hereford, 2009):
\begin{equation} LA=\frac{W_{\text{native}}-W_{non-native}}{\text{avg\ }(W)}\text{\ \ \ }\nonumber \\ \end{equation}
Where W represents the mean fitness of native and nonnative populations, and avg (W ) represents the mean fitness of all populations. In this study, the early-season WR populations were native in early rice-cultivation season, and the late-season WR populations were native in late rice-cultivation season. Generally, positive LA values indicate local adaptation in the native populations (Hereford, 2009). However, the negative LA values of flowering time also indicate local adaptation for early flowering in WR.