Abstract
We recorded sunlight intensity at anthesis of 390 rice landraces flowering in the short-day season in a year, and find that flower opening time (FOT) is delayed but flower exposure duration (FED) is shortened on cloudy days (<30000 lux). These results construe a reversal of the effect previously reported from a larger set of 1114 landaces (including the 390 landraces in this study), recorded during short-day and long-day seasons over 3 years. To resolve this Simpson’s paradox, we subsequently recorded solar illuminance at FOT of 25 landrace populations, half of which was fully exposed to the sun, compared to another half under shade. This experiment revealed that low sunlight intensity, mimicking cloudy days, significantly delays FOT, corroborating the pattern detected in our earlier findings. However, experimental shading has an indeterminate effect on FED of the same landraces. We hypothesize that the delayed FOT on overcast days is an adaptation in rice plants in anticipation of rain, for protection of the pollen from rainwash.
Highlights Low solar illuminance significantly delays flower-opening time in rice landraces. However, the effect of experimental shading on flower opening duration of the same landraces is indeterminate, likely due to blocking of sunlight.
Competing Interest Statement
The authors have declared no competing interest.
List of Abbreviations
- FCT
- Flower closing time
- FD
- (First) flowering date
- FED
- Flower exposure duration
- FOT
- Flower opening time
- IQR
- Interquartile range
- SAD
- Sunrise-to-anthesis duration
