Identifying the Promising Drought Tolerant Genotypes Having High WUE Using Extreme Values of d 13C and d 18O Ratios.

High water use efficiency (WUE) genotypes could be used to improve drought tolerance under water-limited conditions. However, increased WUE is often associated with reduction in transpiration (T), which is often accompanied by a reduction in biomass. In this research, the ¹³C:¹²C   ¹³C) and ¹⁸O:¹⁶O  ¹⁸O) ratios were used as surrogate measurement for WUE and T, respectively. From a panel of 373 MG IV accessions, five genotypes from extreme groups having either high or low  ¹³C and for having high or low  ¹⁸O were chosen based on their phenotypic values and marker effects, similar to methods used in genomic selection. The study’s objective was to identify the genotypes with high WUE associated with relatively high T, and hence, high rate of biomass production. Growth chamber and field experiments were conducted to evaluate the different extremes under well-watered and drought conditions. In the growth chamber experiment, transpiration data, based on gravimetrical measurements, and WUE were estimated. Measured WUE in this study was positively correlated to both  ¹³C and  ¹⁸O. In the field experiment, canopy wilting and temperature were recorded. In the growth chamber experiment, significant difference in extreme groups and genotypes within group were observed. The genotype group having high  ¹³C and high  ¹⁸O also had higher WUE. From the field experiment, extreme group and genotypes within group showed significant differences for canopy temperature and wilting. Genotype PI567572B had both higher WUE and also had slower canopy wilting.