**2.1 Materials and methods**

Experiment 1 was conducted on an experimental field of Shimane University in Matsue, Shimane Prefecture, Japan (35°29'N, 133°04'E, 4 m above sea level) in 2010. Three indica cultivars and four japonica cultivars with wide ranges of flower opening times (Kobayasi et al., 2010) were used (Table 1). 'Xiaomazhan' had the earliest flower opening time in Japan (Kobayasi et al., 2010) and in Jiangsu Province, China (Zhao et al., 2010) among indica and japonica cultivars. Among japonica cultivars, 'Milky Queen' had the earliest flower opening time in Japan (Kobayasi et al., 2010) and in Jiangsu Province, China (Zhao et al., 2010). Although indica cultivars are not commonly planted in Japan, we used 'IR72' and 'Takanari' because the flowers of indica cultivars open earlier than those of japonica cultivars (Imaki et al., 1987).

The soil type at the study site was alluvial sandy clay. On three occasions, 30-day-old seedlings grown in nursery boxes were manually transplanted to the experimental field of Shimane University to obtain flowering plants under different weather conditions. Table 1 shows the seeding dates, ecotype, origin, and measurement periods for the flower opening time and weather factors. The planting density was 22.2 hills m−2 (one seedling per hill, 15 cm hill spacing, and 30-cm row spacing). The area of each plot was 12.8 m2. A basal dressing of 4.0 g m−2 of N, 4.9 g m−2 of P2O5, and 4.3 g m−2 of K2O was applied. Top dressing was not used. Culture methods such as irrigation and pesticide used followed the standard local practices for rice production in Shimane Prefecture.


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

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

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 occasionally difficult.

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 microclimate (Buck, 1981).
