Inheritance and Physiological Effects of Stomatal Frequency in Barley1

We studied inheritance of Stomatal frequency in five barley (Hordeum vulgareL.), populations and the effect of Stomatal frequency on photosynthesis, transpiration, and Stomatal resistance to diffusion. The latter studies were done using barley lines high and low in Stomatal frequency from two backcross populations. Heritabilities, estimated by the parent‐progeny regression method, ranged from 22 to 74%. These estimates were for the F2and F3generations on the individual plant basis. Realized heritabilities based on simulated high and low selection were in good agreement with the regression estimates, although the estimates were consistently higher for the high than for the low selection. For plants pretreated to assure open stomata, Stomatal diffusive resistances and transpiration rates differed statistically among lines, but photosynthesis did not. Lines having low Stomatal frequencies had higher Stomatal resistances, and transpired less water than lines with more stomata. A 25% decrease in frequency of stomata reduced transpiration rates by about 24%. Stomatal frequency did not influence the rate of photosynthesis, however. Hence, the possibility exists of altering transpiration without altering photosynthesis by selecting varieties with fewer stomata.