Studies on drought resistance in Sorghum bicolor L. Muench Leaf water parameters in different growth stages

The different leaf water parameters, Le., totalleaf water potential (\}Jt), leaf osmotic potential at full turgor ('P S100) leaf osmotic potential at zero turgor (\PSO), relative water content at zero turgor (RWCO) and relative dry weight of the leaf (RDW) were studied during four growth stages in five varieties of sweet sorghum under various soil moisture regimes. In all the varieties, severely stressed plants under 30 % field capacity (FC) conditions showed the most negative noon \fit, whereas plants grown under the highest soil moisture regimes (70 % FC) showed the least negative noon 'Pt. The varieties X-BIBO and 301 exhibited a similar potential to adjust osmotically in the dry environment. The range of their osmotic adjustment was from 0.20 to 0.50 MPa. Both varieties showed the highest sensitivity to drought during the dough stage of growth, but only in variety X-8180 the decrease in \Ps values was sufficient to maintain leaf turgor. The variety Red Top Candy was found to be moderately resistant, the extent of osmotic adjustment ranging from 0.10 to 0.25 MPa. This variety also showed less capacity for osmotic adjustment du ring the milk stage of growth. The variety Keller did not show any significant amount of osmotic adjustment. In the variety 405 only a weak tendency of osmotic adjustment was found during the flowering stage of growth.