Investigation on yield improvement and development under drought condition using breeding techniques is difficult, due to the association with low heritability of specific traits. Even more, investigation of physiological indicators (stomatal conductance, chlorophyll index, relative water content, chlorophyll fluorescence, canopy temperature, radiation use efficiency, stay-green etc.) is of interest as they are more accessible, with a low cost, therefore these indicators of physiological traits can be used as good criteria in selecting valuable species. In order to evaluate the effects of water stress on grain yield, its components and some physiological traits of grain sorghum genotypes (Sorghum bicolor L.), a field experiment using split plot design with three replications was carried. The main plots included three water stress treatments: normal irrigation as control, halting irrigation at the stage of terminal leaf emergence and halting irrigation at the stage of 50% flowering. The sub-plots included 10 genotypes of sorghum (‘KGS29’, ‘MGS2’, ‘Sepideh’, ‘KGFS27’, ‘MGS5’, ‘KGFS5’, ‘KGFS17’, ‘KGFS13’ and ‘KGFS30’). Results showed that water stress significantly decreased grain yield and its components (1,000 seed weight, number of seed per panicle) and had various effects on physiological traits. The water stress increased canopy temperature and radiation use efficiency, while stomatal conductance, chlorophyll index (SPAD) and stay-green of genotypes were decreased; the maximum efficiency of photosystem II of photosynthesis remained unchanged between the treatments. Genotypes turned out to have significantly different responses to the drought treatments for all the studied traits, indicating the existence of a high variability among them. In general, physiological traits could be used as good indicators in water stress investigations and might provide comprehensive information as compared with morphological traits.

The purpose of this experiment is to compare the growth and water consumption efficiency of five garden plants (marigold (Tagetes erecta ‘Red Brocade’), moss-rose (Portulaca grandiflora ‘Sun Rose’), dahlia (Dahlia sp. ‘Double Opra’), gazania (Gazania splendens ‘New Day’), and Indian blanket (Gaillardia pulchella. ‘Sun Dance’)) during the warmer seasons of the year under various levels of drought stress based on field capacity (FC; 25, 50, 75, and 100 %). The interaction effect of plant × drought stress (FC) on the fresh and dry mass of aerial and underground organs was significant. Decreased water availability resulted in a drop in growth parameters (leaf fresh and dry mass and leaf area). In compared to the growth of aerial organs, root biomass increased in response to drought stress. Marigold, Indian blanket, and dahlia plants had the highest root-to-shoot ratio in extreme stress, i.e., FC 25 %. The plant × drought stress interaction significantly influenced flower number, whereas flower diameter was influenced by the main effect of plant and drought stress (not their interaction). The FC 100 % and FC 25 % treatments had the highest and the lowest accumulations of proline and soluble sugars, respectively. Moss-rose, gazania, and marigold ornamental plants had the highest water use efficiency at 75 %, followed by Dahlia at 50 % and moss-rose at 25 %.