Diversity of Flower Opening Time and Duration in Rice (Oryza sativa ssp. indica) Landraces of South and Southeast Asia in Different Cultivation Seasons

Different cultivars of rice (Oryza sativa) open at different times of the day, and the overlap of anthesis time in rice between the neighbouring cultivars is of crucial importance to the degree of cross pollination in rice. Nevertheless, none of the past experiments with cross pollination between different rice cultivars ever reported the respective flower opening time (FOT) and flower exposure duration (FED) of the parent cultivars, until recently. The authors present here the first record of FOT and FED of 1114 indica rice landraces of South and Southeast Asia, growing during summer and winter seasons in three consecutive years. The authors also present an analysis of the influences of the growing season on the anthesis behaviour, and present the first records of the FOT and FED variability on sunny and cloudy days of a large number of landraces. The data show that rice florets tend to open later in the morning (that is, take longer time to anthesis after sunrise) on sunny days than on cloudy days, and also significantly later during long day seasons (spring and summer) than during short day season (winter); and that FED is inversely related to both FOT and the length of duration from sunrise to first flower opening. The wide ranges of FOT (8:50 a.m. to 12:40 p.m.) and FED (15 to 194 minutes) also suggest the ample time window for receiving pollen from neighbouring cultivars with different FOT, enhancing the chances of cross pollination between hundreds of rice landraces with FOT and FED overlaps.