EFFECTS OF HIGH-TEMPERATURE AND CO2 CONCENTRATION ON SPIKELET STERILITY IN INDICA RICE

The effects of increasing temperature and CO2 concentration on floral sterility were examined for rice (cv. IR 72) using open-top chambers l ocated at the International Rice Research Institute in Los Banes, Phil ippines. The field-based open-top chamber system was used to simulate four different environments: ambient temperature and CO2 concentration (control); ambient temperature, ambient +300 mu l l(-1) CO2; ambient +4 degrees C temperature, ambient CO2 concentration; ambient +4 degree s C temperature, ambient + 300 mu 1 l(-1) CO2. High temperature during flowering resulted in increased pollen sterility with the degree of s terility exacerbated if rice was exposed to both high temperature and increased CO2 concentration. The critical air temperature for spikelet sterility (as determined from the number of germinated pollen grains on the stigma) was reduced by ca 1 degrees C at elevated concentration s of carbon dioxide. We speculate that this downward shift in critical temperature may be due to the observed increase in air temperature wi thin the canopy at high CO2 concentrations. This increase in air tempe rature, in turn, may be related to stomatal closure and reduced transp irational cooling in an elevated CO2 environment. Data from this exper iment indicate that increasing CO2 concentration could limit rice yiel d if average air temperature increased simultaneously.