A Meta-Analysis of the Effects of Drought Stress on Agronomic and Yield-Related Traits in Sorghum
Sorghum (Sorghum bicolor [L.] Moench) is a nutritious crop widely adapted to grow in arid and semi-arid agro-ecologies, supporting millions of households, and it has the potential to enhance soil health. However, extreme drought and heat stress conditions curtail its yield potential, requiring global efforts to develop drought-tolerant and agronomically superior cultivars. The objective of this paper was to quantitatively assess the impact of drought stress on sorghum genotypes for agronomic and yield-related traits, based on global breeding efforts for drought-tolerant varieties to guide current and future improvement programmes. The study involved a meta-analysis based on 30 selected research papers published around the world that reported on sorghum agronomic and yield-related traits under non-stress (NS) and drought stress (DS) conditions. Data were extracted for the following vital traits: days to 50% flowering (DTF), days to 50% maturity (DTM), plant height (PH), number of tillers (TN), panicle length (PL), panicle width (PW), shoot biomass (SB), root biomass (RB), root-to-shoot biomass ratio (RS), stay green (SG), and grain yield (GY). The sorghum genotypes reported with drought tolerance exhibited a mean GY value of 3.30 t ha−1, ranging from 0.55 to 8.39 t ha−1 under DS conditions. Under NS conditions, the mean GY was 4.38 t ha−1, with the top genotype scoring a GY of 14.1 t ha−1. Drought reduced TN and GY by 42.12% and 27.18%, followed by PW (25.52%) and SB (22.12%)—in that order. The forest plot analysis revealed that drought had a negative effect on the assessed traits, highlighting the need for developing drought-tolerant cultivars. The highest effect sizes were calculated for TN (−1.83), followed by PW (−1.69), and SB (−1.33), whereas PL (−0.1) had the lowest, suggesting that PW and SB are critical for selection in drought-tolerance breeding. Under DS conditions, GY exhibited positive correlations with RS (r = 0.63), RB (r = 0.50), SB (r = 0.27), DTM (r = 0.26), and SG (r = 0.21). The findings of this study could guide future breeding efforts to develop drought-tolerant sorghum varieties.