Résumé
•Closely related pearl millet lines (backcrossed inbred lines) differ in rhizosheath size.•Larger rhizosheath tend to maintain better soil moisture under water deficit.•High-rhizosheath lines maintain better plant growth and root integrity under water deficit.
Plants have evolved adaptive strategies to enhance hydromineral uptake, with rhizosheath formation emerging as a key mechanism improving water deficit tolerance. In pearl millet (Cenchrus americanus syn Pennisetum glaucum), intraspecific genetic diversity exists in rhizosheath formation and root traits, differences in rhizosheath size correlating with shifts in rhizosphere bacterial composition and diversity. However, the role of rhizosheath size in pearl millet response to abiotic stresses remains unclear. Determining whether rhizosheath size improves drought tolerance would help identifying root-soil interactions characteristics that enhance pearl millet resilience. To investigate this, we conducted a study using four pairs of closely pearl millet lines contrasting in rhizosheath size. Plants were grown in an arenosol under greenhouse conditions. After three weeks of irrigation, they were subjected to two water stress regimes (partial and severe deficit) for two weeks, alongside a well-watered control. Under water stress, rhizosheath mass was positively correlated with soil moisture, plant biomass, leaf water potential (Ψl), and several root traits (length, diameter, area, volume; p < 0.001). Under moderate water stress, high-rhizosheath lines (HRL) maintained higher Ψl (-2.07 MPa vs. -2.63 MPa) and exhibited less shoot biomass reduction (14 % vs. 25 %) than low-rhizosheath lines (LRL). Under severe stress, HRL showed greater resilience, with a smaller root biomass reduction (54 % vs. 71 %). These results suggest that lines with more developed rhizosheath tend to maintain root system development and sustain plant growth under moderate water deficit, likely by improving rhizosphere water retention. Our work supports incorporating rhizosheath traits in pearl millet breeding programs to enhance drought tolerance.