Weighted geometric mean index: A model to evaluate drought tolerance in post-rainy season sorghum (Sorghum bicolor (L.) Moench)

In India, post-rainy season sorghum, a cereal crop is very crucial for food and fodder security in the drought prone areas. The aim of this study was to provide an improved or better index to identify drought-tolerant genotypes. Stress susceptible index (SSI) is currently the most commonly used index by plant breeders globally to select drought-tolerant genotypes. However, SSI has certain limitations which can be addressed by new index, i.e., weighted geometric mean index (WGMI). In the present study, 42 and 25 genotypes were evaluated under three environments during the post-rainy seasons of 2015–2016 and 2016–2017, respectively, using split plot design. Genotypes were categorized as tolerant, moderately tolerant and susceptible using model WGMI. Significant and negative correlations were observed between WGMI and SSI for grain and stover yield in most of the cases. The best index to identify drought-tolerant genotypes must be highly significantly correlated with traits under stress and non-stress environments. In this context, our proposed index demonstrated higher correlation with grain and stover yield in comparison with SSI and higher coefficient of determination to identify drought-tolerant genotypes. WGMI was found to be more appropriate and reliable indicator, as it gives information regarding higher yield along with drought tolerance. In addition, it was shown to provide information on wide adaptability of genotypes under several environments. The correlation studies suggested that the traits associated with drought tolerance were early flowering, longer peduncle length and higher panicle emergence (percent).