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.