Transpiration Ratio in Sorghum [Sorghum bicolor (L.) Moench] for Increased Water-use Efficiency and Drought Tolerance

There is an increasing need to improve crop water-use efficiency (WUE) (i.e., the ratio of whole-plant biomass to cumulative transpiration) due to decreased water availability and increased food and energy demands throughout the world. In previous studies, the pre-flowering transpiration ratio (A:E) [CO2 assimilation rate (A) divided by transpiration rate (E)] of sorghum leaves was correlated with WUE. The present greenhouse study was conducted to examine pre-flower A:E in 70 inbred sorghum (Sorghum bicolor L. Moench) lines and two parents (Tx430 and Tx7078) in terms of phenotypic and genetic variation. Parents were selected with contrasting A:E based on previous studies. The experimental design was a Randomized Complete Block, with genotype (70 inbred lines and the parents) and water regime (40 and 80% of “field capacity” (FC)) as experimental factors, and four replications. Genotype had a highly significant effect on A, E and A:E. Frequency distribution for A:E revealed the normal distribution indicating the polygenic segregation among the progenies. Average A:E was 3.07 mmol CO2 mol-1 H2O for Tx430 and 2.80 for Tx7078. These results provide further evidence that there is genetic variability among genotypes for gas exchange rates at pre-flowering in sorghum suggesting scope for improved WUE and productivity.