Abstract
Leaf appearance and leaf elongation rates in rice play an essential role in determining the development of the plants’ architecture which affects their adaptability to varying environments. This study aimed to characterize the rates of leaf appearance and elongation on all leaves of the main culms of rice plants for 11 contrasting varieties and to determine if the decrease in the leaf appearance rate was related to a simultaneous decrease in the rate of leaf elongation. Forty four 13-L pots were sown with one plant from one genotype and laid out in 4 randomized complete blocks. The experiment, conducted inside a greenhouse, was repeated twice. The increase in length of the leaves expanding on the main stems was monitored daily until flag leaf. Data were used to estimate the rates of leaf appearance and leaf elongation. Significant variability in the rate of leaf appearance, rate of leaf elongation, and leaf length was found across varieties. The kinetics of leaf appearance had linear phases intermediated by a curvilinear phase, without sharp changes in the phyllochron duration. Maximal leaf elongation rate (LER) of all genotypes (except for one) increased linearly with leaf rank until it reached its maximum value at leaf 8 to 10 (11 - 12 for Azucena) where it stabilized before decreasing linearly with leaf rank for the last leaves. Finally, both rates of leaf appearance and leaf elongation evolved with time more smoothly than expected so no sharp decrease in LER occurred at the time of the decrease in leaf appearance rate of the last leaves. However, the trilinear model fits the data well enough to remain useful in efficiently comparing the leaf appearance kinetics of contrasting varieties.
Highlights
Leaf appearance rate in cereal follows a regular rhythm when timed in thermal time [1]
The average relative humidity was the same (72.5%) for both sowing dates while the mean photosynthetically active radiation (PAR) transmitted into the greenhouse was higher for the June (4.8 MJ·m−2) than for the September sowing (3.5 MJ·m−2)
The leaf appearance kinetics by variety was very similar between sowing dates
Summary
Leaf appearance rate in cereal follows a regular rhythm when timed in thermal time [1]. The leaves are found to appear at regular time intervals (phyllochrons) as influenced by environmental factors such as temperature, day length, mineral nutrition, light intensity, planting density, and humidity [3]. The second inflection in the leaf appearance rate was found to occur earlier with a longer phyllochron compared to flooded conditions [5]. This second decrease in the leaf appearance rate was initially believed to be associated with the panicle initiation and later with the onset of the internode elongation [6]. It would be useful to fully understand these processes to be able to control them in the improvement of the adaptation of the rice plant to aerobic environments
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