Relative contribution of stomatal parameters in influencing WUE among rice mutants differing in leaf mass area

Water use efficiency (WUE) is an important physiological trait that has potential in sustaining crop productivity under water-limited condition. WUE can be increased by improving carbon gain and/or reducing transpiration. Normally, carbon gain and transpiration are inter-related and hence a trade-off exists between transpiration and WUE. Therefore, factors that influence these traits and their inter-relationship need to be identified and characterised. Here we report that leaf mass area (LMA) has one such trait that regulate WUE by influencing carbon gain. Extensive screening of EMS induced mutant population of Nagina-22 (N22) led to identification of contrasting LMA mutants. The high LMA mutant with 27% higher LMA (5.10 mg cm −2 ) than N22, and a low LMA mutant (4.00 mg cm −2 ) with comparable canopy leaf area and root weight were selected to study the influence of stomatal density and size on cumulative water transpired (CWT) and WUE under two soil moisture conditions (100% FC and 50% FC). The high LMA mutant, had higher stomatal density leading to increased CWT. But, a reduction in stomatal size on both abaxial and adaxial surfaces under water-limited conditions did not influence CWT. Increased photosynthetic efficiency due to higher leaf thickness led to higher carbon gain and hence higher WUE. The results indicate that improving carbon assimilation through higher LMA would significantly circumvent the trade-off between water loss and biomass accumulation leading to higher WUE. Thus, high chloroplast capacity types would have higher WUE despite relatively high water use.