Résumé
To improve sugarcane resilience to water stress, increasingly frequent in the Indian ocean region, varietal tolerance is a promising approach to mitigate the risk. Water-use-associated traits are known to be genetic in many crops and can be interesting target for breeding but remain difficult to measure. An ex-situ mini-lysimetric platform has been established at the CIRAD research station in La Bretagne (La Réunion). This setup enables, for the first time in sugarcane, direct and non-modelled measurement of water use efficiency (WUE, defined as biomass produced per unit of water consumed) at the varietal level and over long period of time. Until now, WUE estimates in sugarcane have relied mostly on modelling approaches, estimation using the crop evapotranspiration potential or instantaneous gas exchange measurements, which are poorly suited for identifying stable and heritable traits. The platform also enables quantification of the atmospheric evaporative demand over the transpiration period using weather data, and direct comparison with the actual transpiration measured for each variety, thus revealing differences in transpiration sensitivity or regulation. The system includes 180 pots and makes it possible to grow 30 different varieties × 6 replicates, arranged with spacing comparable to field planting density and randomly disposed on the platform. Each pot is placed in a sealed container to prevent putative drainage resulting from irrigation and covered with recycled plastic mulch to eliminate surface evaporation. This ensures that all water loss is attributable solely to plant transpiration. Weekly weight measurements are taken using a mobile precision scale (150 kg capacity, 10 g resolution), while a weather station on site records environmental data to calculate evaporative demand (ET₀, VPD). The varietal panel was selected to represent a gradient of genetic improvement of sugarcane (Saccharum spp.): it includes accessions of the wild S. spontaneum species, accessions from the first three early introgression generations of S. spontaneum into elite sugar-producing germplasm (pseudo 'F1', 'BC1' and 'BC2' accessions) “, as well as elite commercial varieties currently grown and adapted to contrasting environments across La Réunion. This simple, low-cost, and easily deployable system enables precise phenotyping of water-use traits in sugarcane up to the end of the tillering stage, a key stage in drought sensitivity. Field trials will be conducted to validate the relevance of these traits for drought tolerance.