2.4 Measurements of fitness related traits
Vegetative growth traits, including plant height, number of tillers per plant, and leaf length/width were measured in the common garden experiments. Plant height was defined as the distance from the ground to the tip of the longest leaf, and number of tillers per plant referred to the total of branches emerged from the main stem culm of a plant. Leaf length and width of the main stem culm were also involved, including the top-first leaf (the first leaf on the top of main stem culm) and top-second leaf (the second leaf on the top of main stem culm). The leaf length was defined as the distance from leaf tip to the base, and the leaf width was measured at the middle of the leaf.
To detect the differences in vegetative growth between the early- and late-season WR populations at different stages, we measured these traits in every 20 days after germination (DAG), including the 20, 40, 60 and 80 DAG. At the 20 DAG, considering the elder seedlings are too weak to avoid the harms during the measurement, the measurements of leaf length and width were abandoned, therefore only plant height and number of tillers per plant were measured. After transplanting, the measurements of plant height, number of tillers, and leaf length/width for each plant individual were conducted in all planting plots at 40, 60 and 80 DAG. Experimental data obtained from the measurements and recording was mainly used to estimate differences in growth and development between the early- and late-season WR populations in the same rice-cultivation season, and to compare the performance of the same population in different rice-cultivation seasons.
The flowering time pattern of each plant from beginning to end was recorded, and a dynamic pattern of flowering time was constructed in each population. The beginning of flowering was defined as the date of the first flower emerging, and the end of flowering was indicated by the rise of heavy panicles. The proportion of flowering plants per day was marked and recorded in each population, which was used to construct the flowering time patterns of weedy rice populations. To estimate more comprehensive differences in flowering time between the early- and late-season WR populations, the average flowering time in different phases, including 1%, 30%, 50% and 80% plants flowered, were also calculated to do further comparisons between the two-season WR populations.
The reproductive traits were closely associated with the flowering time in rice. Therefore, the number of seeds per plant, seed setting ratio and 100-seeds weight were measured for each plot. After harvesting and threshing, full seeds were separated by a seed air cleaning instrument (CFY-2, Top Cloud-agri Technology Company, Zhejiang, China), and seeds counting using electronic seed counter (PME, Shanco Instruments, Shanghai, China) and 100-seeds weighting using analytical balance.