Stress Tolerance Index- A New Indicator of Tolerance

Selection criteria for identifying genotypes with high stress tolerance and high yielding potentials were compared using a moderately stressed, (Stress intensity, [1-(mean stress yield (Y p̄ )/mean potential yield (Y s̄ )] 0.73) and a severely stressed (Stress intensity, 0.24) mungbean yield data sets. Selection based on tolerance (T), difference between potential yield (Y p ) and the yield in stress environment (Y s ) favored genotypes with tolerance and low yield potentials. Selection based on the mean productivity (MP), [MP=(Y p +Y s )/2] favored the genotypes with high yielding potential. The Stress Susceptibility Index (S), (S = [(Y p -Y s )/Y p ]/[(Y p̄ -Y s̄ )/Y p̄ ], also favored the low yielding and stress tolerant genotypes. These selection criteria failed to identify genotypes with high yielding and stress tolerance potentials. Thus, a selection criterion, Stress Tolerance Index (STI) is proposed here which identifies genotypes with high yield and stress tolerance potentials. The STI takes into account both stress tolerance and yield potentials. The STI is estimated as: [Y p /Y p̄ ][1-(T/Yp̄)]. The higher the value of STI for a genotype in a given stressed environment, the higher was its stress tolerance and yield potential. The interrelationships between these stress tolerance criteria are discussed by a biplot display.