Effect of drought stress on residual transpiration and its relationship with water use of wheat

Increasing the water use efficiency (WUE) of wheat (Triticum spp.) has long been a goal in semiarid areas. Low rates of residual (cuticular) transpiration are thought to improve yield potential of wheat under dry conditions, although the linkage is tenuous. The objective of this work was to investigate the association of residual transpiration with water use, WUE, and leaf water status in hexaploid (T. aestivum L.) and tetraploid (T. turgidum L. var. durum) genotypes grown under two watering regimes in two glasshouse experiments. Single plants were grown in 0.1-m × 1-m (0.1-m × 0.5-m in exp. 2 low-stress treatment) PVC tubes filled with soil. The watering regimes consisted of weekly replenishment of water used (low stress), or addition of sufficient water to ensure plant survival (high stress). At anthesis, flag leaf residual transpiration (rate of water loss from excised leaves), stomatal conductance, relative water content (RWC), and osmotic potential (exp. 1 only) were measured. Water use was not correlated with residual transpiration rate in either experiment. Residual transpiration rate did not differ for the two stress treatments in exp. 1, but there were significant (P < 0.01) genotype by stress treatment interactions. Residual transpiration rate was not related to plant water status (leaf RWC or osmotic potential) as had been reported in other studies. Key words: Cuticular transpiration, water use efficiency, Triticum aestivum L., Triticum turgidum L. var. durum

THE EFFECTS OF GLAUCOUSNESS, EPICUTICULAR WAX, LEAF AGE, PLANT HEIGHT, AND GROWTH ENVIRONMENT ON WATER LOSS RATES OF EXCISED WHEAT LEAVES

Water loss at minimum stomatal aperture (residual transpiration) from plant surfaces accounts for a substantial proportion of total transpiration during periods of water stress and at night. Its reduction by genetic selection has been suggested as a desirable objective in water-limited environments. To identify genetic and environmental sources of variation in residual transpiration of wheat (Triticum spp.), the effects of glaucousness, epicuticular wax, leaf age, plant height, and growth environment were determined using excised leaves. Glaucousness reduced residual transpiration by an average of 10%. Differing quantities of epicuticular wax and glaucousness in an isogenic pair of genotypes affected residual transpiration as well, the rate being 33% greater in the low wax, nonglaucous than in the high wax, glaucous line. Residual transpiration rate of flag leaves of field-grown plants increased with leaf age, particularly during the 7 d following ligule appearance. The rate of residual transpiration was greater in tall than in dwarf near-isogenic lines. Residual transpiration of leaves from plants grown in glasshouses was 44–66% lower than that of plants grown outdoors, which had a mean rate of 2.68 × 10−5 g H2O cm−2 min−1. Method of water application to glasshouse plants influenced residual transpiration rate. The rate for leaves of plants watered by spraying water onto the plant and soil surface was 20% greater than that of leaves of plants watered on the soil surface only. It was concluded that the increase in residual transpiration rate with leaf age was due to duration of exposure to the rigors of the exterior environment; the absence of this in controlled environments results in lower rates of residual transpiration than in the field.Key words: Cuticular transpiration, Triticum aestivum L., Triticum turgidum L. var. durum, wheat