Influence of Osmotic Adjustment on the Growth, Stomatal Conductance and Light Interception of Contrasting Sorghum Lines in a Harsh Environment

Abstract

Two drought resistant lines of sorghum, IS 13441 and IS 1347, with a high capacity for osmotic adjustment and two susceptible lines, IS 12739 and IS 12744, were subjected to drought in the field during a summer season in the semi-arid tropics in India. During this season there is little rain, air temperatures reach 42°C, and pan evaporation rates may reach 20 mm d-1 providing a harsh environment for crop growth. Most of the osmotic adjustment occurred within 3 weeks after withholding water and at high predawn leaf water potentials, i.e. at values above - 1.0 MPa. As a result, resistant lines were able to maintain a positive turgor to lower leaf water potentials (- 2.8 MPa) than susceptible lines (- 2.0 MPa). Nevertheless, dry matter production was negligible in both resistant and susceptible lines when predawn leaf water potentials fell to - 0.55 MPa. Furthermore, throughout the drought period the leaf area of all water-stressed plants was similar when expressed relative to the control regardless of the level of osmotic adjustment. Resistant lines had similar stomatal response to leaf water potential as susceptible lines. Large changes occurred in stomatal conductance and leaf rolling soon after withholding water while there was considerable osmotic adjustment in the leaves. Leaf rolling coincided with a reduction in the ability of the plant to utilise radiation. Therefore, even if osmotic adjustment had delayed leaf rolling, the gain in productivity would be small. On the basis of these turgor related processes it can be concluded that there would be little advantage in selecting for plants with a higher capacity for osmotic adjustment in this harsh environment.

Genotypic Variation in Root Anatomy, Starch Accumulation, and Protein Induction in Upland Rice (Oryza sativa) Varieties Under Water Stress

“…Liu et al [21] also suggested that water status probably has a more direct effect on spikelet fertility, grain filling, and, finally, yield. It has been reported that water potential of well-watered plants can decline with ontogeny due to increasing demand for water as the leaf area increases [9]. In this study, water potential in the watered plants was maintained in the range that well-watered plants are expected to maintain [40].…”

Effect of Water Stress on Moisture Content Distribution in Soil and Morphological Characters of Two Tomato (<i>Lycopersicon esculentum Mill</i>) Cultivars

“…followed by 40%FC and control. The ability of the cultivars to produce dry matter under depleted soil moisture regimes might be due to the effect of osmotic adjustment [10,11].…”

Osmolyte accumulation: can it really help increase crop yield under drought conditions?

“…Grumet, Albrechtsen & Handon (1987) reported that barley lines selected for high osmotic adjustment had slower growth, lower dry matter production and grain yield than lines with low osmotic adjustment. No yield benefit was found with osmotic adjustment in four sorghum cultivars under severe drought (Flower, Rani & Peacock 1990). Recently, Subbarao, Chauhan & Johansen (2000) reported that OA was positively correlated with grain yields at 72 and 82 days after sowing (DAS) whereas OA at 92 DAS contributed negatively to the yield.…”