Differential Tolerances Among Tropical Forage Crops to Water Deficit Conditions.

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The objective of this study are evaluation of morphological and physiological adaptation of the crops to water stress conditions to estimate their drought to lerant ability. Plant were grown foth in green house, field condition and water culture and subjected to sequence to water stress. The plant growth of tested plants was Affected remarkably due to water stress. The Relative Growth Rate (RGR) and Net Ossimilation Rate (NAR) decreased under stress conditions and significant differences were observed between crop species. The reduction percentage in RGR and NAR under water stress condition was used as an indicator of tolerances to drought. It was low in Rhodesgrass and high in Jod's tears. However, Leaf Area Ratio (LAR) was not effected by stress. The photosynthetic rate was reduced due to water stress, spedially in Job's tears. Water use efficiency in Rhodesgrass was increased by strees, whereas that of Job's tears was severely decreased. Rhodesgrass was capable of maintaining photos … More ynthetic production under stress and therefore RGR and NAR were not decreased considerably compared to other crops under stress conditions. ^<14>C aseimitates remedied in leaves and stems and the tanslocation of ^<14>C assimilates from leaves to rots was remarkably reduced under stress conditions in sorghum and Job's tears. ^<14>C content in high-molecular weight constituents such as protein and ligin-cellulose fraction in rots was apparently reduced by stress in Job's tears. And also root hydrautic conductivity (RAC) was considerably longer due to stress. The RHC of Rhodesgrass was there times longer than of Job's tears. The movement of ^3H_2O through plant were remerbobly reduced in both species under water stress. Twenty-Foun hours after added of ^3H_2O, the relative radioactivity in tissue water of root, stem, expanded leaves and ehponding leaves were 15, 45, 9.5 and 8.5% respectively, compared to that of nutrient solution on Rhodeagrass. The respective values in Job's tears were 48, 17, 5.1 and 3.8%. The movement of ^3H_2O from root to shoots, especially to leaves was strongly restrictebl in Job's tears compared to Rhodesgrass. The results indicated that the resistance to water how through plants differ among species according with their drought to lerant ability. The major resistance to water how through plant appers to be exist in the nodes and for the basal stems which are located in transit positions appears from organ to another. Less