Selection efficiency of yield based drought tolerance indices to identify superior sorghum [Sorghum bicolor (L.) Moench] near isogenic lines (NILs) under two-contrasting environments

Drought is the most significant environmental calamity on sorghum in Ethiopia and hence improving yield under drought is a major goal of plant breeding. This study was designed to introgress drought tolerant genes into adapted varieties through marker-assisted backcrossing and select based on tolerance indices. Sixty-one backcrossed lines and along with their nine parental lines were evaluated under full-irrigation and water-limited condition in Alpha lattice design with three replications. Yield-based drought tolerance indices including stress tolerance index (STI), mean relative performance (MRP), geometric mean productivity (GMP), harmonic mean (HM), mean productivity(MP), tolerance index (TOL), stress susceptible index(SSI), yield stability index (YSI) and yield index (YI)were calculated based on yield obtained from the two moisture regimes. Results showed that genotypes differed significantly in yield and their indices. Mean grain yields that varied widely in stressed (1.1 to 4.42 t ha-1) and full-irrigation (2.25 to 5.71 t ha-1) were 1.93 and 3.7 t ha-1, respectively. Of the backcrossed lines, four (BC2F3_ETSC_16258,BC2F3_ETSC_16216, BC2F3_ETSC_16257, and BC2F3_ETSC_16213) were top yielding in stressed conditions with values of 4.42, 3.5, 3.1, and 2.83 t ha-1, respectively. These progenies also showed consistently higher values of STI, MRP, GMP, HM, MP, YSI, and YI and lower values of SSI and TOL indicating less sensitive to stress. The correlation and principal component analyses also revealed STI, MRP, GMP, HM, MP and YI showed highly significant positive correlation among themselves and yield in both environments, indicating their suitability for identifying superior genotypes. Overall, STI, MRP, GMP, HM and MP indices can be efficiently exploited to screen drought tolerance or superior genotype(s) under both moisture conditions.