Epidermal conductance, stomatal density and stomatal size among genotypes of Sorghum bicolor (L.) Moench

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Abstract
The ability of a plant to survive severe water deficits depends on its ability to restrict water loss through the leaf epidermis after stomata attain minimum aperture. At this stage, the rate of water loss is regulated by the epidermal conductance (gc). Low gc would be a useful selection criterion to identify genotypes with enhanced survival capability. Consequently, variation in gc among Sorghum bicolor (L.) Moench genotypes was evaluated. Since there is little conclusive evidence linking gc with leaf waxiness, alternative hypotheses relating gc to stomatal trails were also examined. Epidermal conductance varied from 6.3 to 17.6mmol m−2 s−1 among sorghum genotypes. It was unrelated to stomatal pore length which varied with genotype and to pore depth which was similar for all genotypes measured. However, gc, increased with increasing stomatal density. This indicates that stomatal density plays a direct role in water loss even at very low conductances. The association of low stomatal density with low gc is consistent with the hypothesis that at the smallest stomata aperture, water loss from the epidermis above guard cell teichodes becomes a significant source of leaf water loss. Since low gc is directly related to crop survival under severe water deficits, it is recommended that genotypes with low gc. be selected using the selection criterion of stomatal density.