By Cécile Julia
Engineer in plant breeding; Ph.D. student in rice ecophysiology, CIRAD-AGAP, Montpellier, France Ph.D. research scholar, Crop Physiology Unit
Crop and Environmental Sciences Division (CESD), IRRI
1315-1415 H, Tuesday, 26 June 2012
Room A, D.L. Umali Auditorium, IRRI
Thermal stress and in particular heat during anthesis causes sterility in rice inflorescences. Rice spikelets open in the morning and close a few hours later. Genotypic variation in the time of day of anthesis is considered an escape mechanism from thermal stress, but little is known on its dependency on environmental conditions.
One traditional, cold-tolerant rice cultivar and three improved tropical rice cultivars were grown in the field in four different climatic environments under flooded conditions to study the environmental response of time of day of anthesis. The time of day when the first spikelets opened, a maximum of spikelets were open and the last spikelets closed was observed daily on a population basis (2m² plots replicated 3 times).
Within the same environment, genotypic differences in time of anthesis and duration of anthesis were small. Across all genotypes and environments, the differences were broader and 80% of the variation of the time of maximum anthesis could be explained with the mean minimum air temperature (Tmin) during the 7 days preceding any given anthesis event. Linear, multiple regression models determined for each cultivar using Tmin and vapor pressure deficit (VPD) observations from the three tropical environments explained 94% of variation of time of anthesis onset and end. Low Tmin thereby delayed and low VPD advanced anthesis processes.
Under the assumption that panicle temperature during anthesis is indeed a major determinant of spikelet fertility in rice, it is concluded that the sensitivity of time of day of anthesis to air temperature and humidity is an effective eco-physiological adaptation of the rice crop.