Variation in streptomycin sensitivity and dark sensitivity of 36 rice genotypes of three different maturity groups and 30 ragi genotypes of two different maturity groups were studied. Streptomycin sensitivity and dark sensitivity of rice and ragi genotypes were expressed in terms of bleaching index (BI) and senescence index (SI), respectively. Genotypes of each maturity group of each crop showed wide variation in their BI / SI values. The objective of this investigation was to find the relationship of the BI / SI parameter with yield, adaptability, and stability in yield performance of rice and ragi genotypes. Yield performance of rice and ragi genotypes were evaluated over 12 and nine environments, respectively. Adaptability and stability analysis were done following the linear regression model of Eberhart and Russell (1966) and the AMMI Stability Value (ASV) of Purchase (1997). BI parameter showed a positive correlation with yielding ability and deviation from regression ($S_d^2$) in both rice and ragi, and a negative correlation with adaptability parameter (b) for all the maturity groups of rice and ragi except in the early ragi group. SI parameter showed a negative correlation with yielding ability for all the maturity groups of rice and ragi except in the early ragi group and a positive correlation with adaptability parameter (b) for all the maturity groups of rice and ragi. This experimental study revealed that sensitivity of rice genotypes to streptomycin (SM) in terms of BI could be used to predict yielding ability of genotypes, and dark sensitivity (SI) could be used to indicate adaptability to rich and poor environments. This novel approach may help the breeder in indirect selection of high-yielding genotypes and genotypes well-adapted to rich or poor environments at an early seedling stage before going for multilocation trials.