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31 33 35 37 39 41

31 33 35 37 39 41

Fig. 5.8. Relative enhancement in yield from a doubling of [CO2] vs. daily maximum air temperature (7~max) averaged over the flowering period (7 days) for rice grown in TGCs. (Adapted from Kim et al, 1996b.)

Fig. 5.9. Percentage of spikelets having ten or more germinated pollen grains vs. maximum temperature during flowering for rice grown at ambient and ambient + 300 mmol CO2 mol-1 and at ambient and ambient + 4°C air temperatures. Vertical and horizontal bars indicate standard error of the means for spikelet sterility and temperature, respectively. (Adapted from Matsui et al., 1997b.)

Fig. 5.9. Percentage of spikelets having ten or more germinated pollen grains vs. maximum temperature during flowering for rice grown at ambient and ambient + 300 mmol CO2 mol-1 and at ambient and ambient + 4°C air temperatures. Vertical and horizontal bars indicate standard error of the means for spikelet sterility and temperature, respectively. (Adapted from Matsui et al., 1997b.)

unknown, increased spikelet temperature under CO2 enrichment due to suppression of transpiration is one possibility. However, temperatures during the few days prior to flowering (Satake and Yoshida, 1976; Matsui et al., 1997a) as well as humidity and wind speed during flowering (Matsui et al., 1997a) have been shown also to influence the magnitude of high-temperature-induced spikelet sterility. Clearly, further research is needed to delineate the specific mechanisms by which high temperatures induce spikelet sterility as well as the role of CO2 enrichment in these processes.

A moderately large genetic variation in the tolerance to high-temperature-induced spikelet sterility has been reported both among and between indica- and japonica-type rice genotypes (Satake and Yoshida, 1976; Matsui et al., 1997a). Some rice cultivars have the ability to flower early in the morning, thus potentially avoiding the damaging effects of higher temperatures later in the day (Imaki et al., 1987). The continued search for rice genotypes having higher tolerance to, and/or the ability to avoid, high-temperature damage to spikelets is important in terms of finding options for mitigating potentially adverse effects of global climate change on rice production.

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