Stomatal conductance (gs) is an important trait responsible for the genotypic difference in gas diffusion for photosynthesis and transpiration in rice (Oryza sativa L.). We measured gs, stomatal density and stomatal length (guard-cell length) at two weeks before heading for 64 accessions from a rice diversity research set of germplasm (RDRS) and for three high-yielding cultivars (HYC) under field conditions. Considerable variations in gs, and stomatal length were observed among varieties in RDRS, and it was considered that RDRS covers the species diversity of the stomatal characteristics in rice. When it was compared among the varieties with similar plant earliness, gs was higher in HYC than in most varieties of RDRS. Stomatal density did not correlate with gs, and there was a negative correlation between stomatal density and stomatal length. However, noticeable variance existed in the latter relation, where HYC exhibited a higher stomatal density and slightly shorter stomatal length than RDRS. High gs in HYC is attributable to their high stomatal density and moderate specific stomatal conductance (gs/stomatal density) while the high-g s varieties in RDRS tended to have a lower stomatal density and higher specific stomatal conductance. Stomatal length is related to specific stomatal conductance, but there are remarkable differences between these traits. Specific stomatal conductance in HYC has not reached the upper limit for their stomatal size, which raises a possibility of further improvement of HYC in gs.
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