European Journal of Sustainable Agroecosystems

Background: Pearl millet [Pennisetum glaucum (L.) R. Br.] is a C4 cereal that underpins food, fodder and nutritional security for nearly 100 million people across the arid and semi-arid tropics of sub-Saharan Africa and South Asia. Under progressively drier and hotter climates, the crop’s productivity increasingly depends on how efficiently each unit of transpired water is converted into biomass and grain—its water-use efficiency (WUE).
Objective: This review synthesises current understanding of the physiological determinants of WUE in pearl millet grown under arid conditions, integrating stomatal, hydraulic, root-architectural and biochemical mechanisms, and evaluating how genomic and agronomic tools translate these traits into cultivar improvement.
Method: A structured literature search of Scopus, Web of Science, PubMed and Google Scholar (2015–2025), supplemented by landmark earlier studies, yielded 38 studies for qualitative synthesis and 24 for comparative analysis.
Result: Constitutive water-conserving traits—low leaf transpiration rate, sensitivity of transpiration to high vapour-pressure deficit (VPD) and elevated leaf abscisic acid—consistently distinguish terminal-drought-tolerant genotypes and conserve soil water for grain filling. A rapidly extending primary root, deep root-length density and aquaporin-mediated regulation of root hydraulic conductivity govern water capture, while osmotic adjustment through proline and glycine betaine and enhanced reactive-oxygen-species scavenging sustain cellular function under stress. Transpiration efficiency varies up to two-fold across germplasm, providing exploitable genetic variation.
Research: gaps remain in field-scale root phenotyping, the genetic control of VPD-limited transpiration, aquaporin gene function, and validation of trait effects under combined drought–heat–salinity stress; genotype-by-environment scaling of laboratory traits is also inconsistent.
Conclusion: WUE in pearl millet is a polygenic, multi-scale outcome rather than a single trait; integrating high-throughput phenotyping, genomic selection and agronomy offers the most credible route to climate-resilient, water-efficient cultivars for smallholder arid systems.