**2.1.2 Statistical analysis**

248 Solar Radiation

May 7, 28

May 7, 28

May 7 July 13–20, 23–27

July 26–31,

July 25–29, August 3–7, 20–25

September 5–11

September 2

August 5–11, 17–21

Cultivar Ecotype Origin Seeding dates Measurement period

'Milky Queen' japonica Japan May 7, 28 August 5–11, 17–21

'IR72' indica Philippines May 7, 28 August 24–29,

'Asahi' japonica Japan May 7, 28 September 2–9

Table 1. Ecotype, origin, seeding dates and measurement periods for the seven *O. sativa*

Physical stimuli such as touch may promote flower opening in rice (Tsuboi, 1961). To avoid this phenomenon, we used digital photographs of the panicles instead of physical inspections. The panicles were photographed at 10-min intervals with waterproof digital cameras (Optio W30, Pentax, Tokyo, Japan) to determine the flower opening time of the seven cultivars. The photographs were automatically taken using cameras. We put the camera on a tripod and used a built-in electronic timer to control the measurement intervals. We recorded the time of anther extrusion of all observable flowers (more than 30% of flowers in a panicle) on the obverse side of approximately 10 panicles per day per cultivar. The medians of anther extrusion time among all observed flowers in each panicle were calculated. The flower opening time was defined as the mean of the medians per day. Recording the anther extrusion time of the flowers behind panicles and leaves was

We measured air temperature, solar radiation, relative humidity, and wind speed every 5 min using a wireless weather station (Wireless Vantage Pro, Davis Instruments, Hayward, CA, USA), which was located at the experimental field of Shimane University (http://www.ipc.shimane-u.ac.jp/weather/station/i/home.html). The weather station was installed at a distance of approximately 5 m from observation plots. The ground surface below the station was covered with grass. We installed a thermometer, hygrometer, solarimeter, barometer, and an anemometer at heights of 150, 150, 180, 150, and 300 cm, respectively. At our study site, the sun rose between 0502 (July 13) and 0547 (September 11); thus, we did not measure solar radiation before twilight. Vapor-pressure deficits were calculated from air temperature and relative humidity using the method based on

'Takanari' indica Japan May 28 August 28–

**2.1.1 Measurements of the flower opening time and weather factors** 

'Fujihikari' japonica Japan April 15,

'Koshihikari' japonica Japan April 15,

'Xiaomazhan' indica China April 15,

cultivars used in Experiment 1.

occasionally difficult.

microclimate (Buck, 1981).

Pearson's correlation analysis was used to identify the relationship between solar radiation and the flower opening time. In this analysis, hourly average of solar radiation values between 0500 and 1000 were used. Correlation analysis was restricted to the period between 0500 and 1000 because sunrise hours during the flower opening time observation periods were around 0500, and flowers of 'Xiaomazhan' usually started to open before 1000. It is possible that the span in which flowers respond to solar radiation before flower opening are different among cultivars, i.e. cultivars with early morning flowering would respond earlier in the morning to solar radiation. Hourly average of solar radiation values were used over seven 1-hr periods based on the mean flower opening time in each cultivar (successive 1-hr periods from 7 hr before the mean flower opening time until 1 hr before the mean flower opening time).

The collected data were analyzed by means of generalized linear models and multiple regression procedures using SPSS (Version 14J for Windows, SPSS Japan Inc., Tokyo, Japan). Because inherent relationships exist among weather factors, relatively high correlations may exist among solar radiation, air temperature, vapor-pressure deficit, and wind speed. Therefore, to evaluate their individual effects as well as cultivar effects on the flower opening time, generalized linear models were used. In this analysis, solar radiation, air temperature, vapor-pressure deficit, and wind speed values were averaged over five 1-hr periods (0500–0600, 0600–0700, 0700–0800, 0800–0900, and 0900–1000). The relative contribution of each weather component to the flower opening time was determined using their standardized partial regression coefficients, and the overall strength of the relationships was quantified using the multiple correlation coefficients. The contribution of solar radiation, air temperature, vapor pressure deficit, and wind speed to the flower opening time in each cultivar was estimated by substituting the obtained weather data in the generalized linear models, and the relative contributions of solar radiation, air temperature, vapor pressure deficit, and wind speed to the flower opening time among the cultivars were evaluated. To examine the role of diurnal changes in solar radiation in determining the flower opening time, multiple correlation coefficients from 1800 on the day before flowering to 0900 on the flowering day were calculated for each cultivar.
