2.2 Flower opening time, spikelet sterility, and monitoring of local air temperatures
Flowering pattern observation and data analysis for the time to reach the peak and end of flower opening (FOT50 and FOT90, respectively) was conducted following the method of Hirabayashi et al., (2015). Using four heading panicles per plot per day, opened spikelets were marked every 30 min by fine-tipped pens, and this flowering observation was continued for more than three days in all sites. FOT50 and FOT90 were calculated using the Koyomi Station software (http://eco.mtk.nao.ac.jp/koyomi/index.html.en) and R program (ver. 3.6.2). Note that FOT50 and FOT 90 were presented as time after dawn. On 22 April of 2018, on Crop 1 in Nay Pyi Taw, opened spikelets were marked with different colored pens following the protocol of Ishimaru et al. (2010); spikelets opened before 0700H were marked with blue pens, those between 0700H-0830H with green pens, those between 0830H-1000H with purple pens, and those after 1000H with black pens. At maturity, marked spikelets marked with different colors were collected and sterility was physically checked. Air temperature during flowering was monitored by the meteorological station installed in each experimental site.