Effect of Growth, Leaf Gas Exchange and Water Use Efficiency of Job’s Tears Under Drought Stress Conditions

In this study, the responses of the drought stress on Job’s tears were evaluated, focused on the water use efficiency (WUE), using four cultivars grown under 100% (Control) and 50% (drought stress) irrigation measured based on evapotranspiration. Our result showed that all cultivars had a lower WUE under drought stress than in normal conditions. The Total transpiration of the whole plant (Total T) and the amount of increased above-ground dry weight (ΔAGDW) were lower in stress conditions than in control. However, the reduction of ΔAGDW due to the drought stress was greater than that of Total T, which was thought to result in lower WUE of Job’s tears. Gas exchange analysis demonstrated the reduction of transpiration rate, net photosynthesis rate and instantaneous water use efficiency by drought stress in all cultivars. Comparing among the cultivars, the variation in ΔAGDW was larger than that in Total T, and WUE was significantly correlated with ΔAGDW but not for Total T. These results indicated that the varietal difference in WUE was attributed to dry matter production rather than transpiration. Among the four cultivars, Obanazawa had the highest WUE and might be a promising cultivar for Job’s tears production under the proceeding with climate changes.