Améliorer la tolérance du maïs à la sécheresse et la productivité du sorgho

Climate change is increasing water scarcity risks, with maize and sorghum facing challenges in water use efficiency despite their C4 metabolism. Maize typically consumes more irrigation water than sorghum in regions like France, yet both crops exhibit high water-use efficiency. Although sorghum is often regarded as drought-tolerant, its grain formation is sensitive to water deficits, limiting its use in arid regions. Genetic research, including gene transfer experiments, has shown potential for improving drought tolerance, but few commercial varieties are available. Tolerant genotypes are currently used in Mexico (maize), East Africa (maize), and India/Australia (sorghum). Maize’s drought tolerance has improved through selection, particularly in temperate regions where newer varieties maintain yields under drought without compromising overall productivity. Tropical maize varieties developed by CIMMYT for drought-prone areas hold untapped potential for European adaptation through the use of teosinte and Tripsacum genetic resources. Drought tolerance strategies are highly scenario-dependent: maintaining grain numbers may reduce yield quality under severe drought, while deep rooting benefits are contingent on soil conditions. No universal solution exists; breeding must prioritise context-specific traits. Sorghum’s reputation for drought tolerance contrasts with its lower productivity compared to maize. It exhibits sensitivity to water deficits, with yield differences of up to 30 q/ha between irrigated and non-irrigated crops in France. Its tolerance may stem from sustained nitrogen uptake and efficient photosynthesis under varying soil moisture. The 'stay-green' trait—prolonging photosynthetic activity post-flowering—is critical for drought resilience. In Europe, sorghum breeding has focused on hybridisation via cytoplasmic male sterility, but progress has been constrained by photoperiod sensitivity and limited exploration of tropical diversity. The USDA’s 1960s programme reduced photoperiod sensitivity, yet sorghum’s productivity potential may be intrinsically limited by cycle length and panicle development rates. Redistributing photosynthates or optimising growth stages could enhance yields without extending cycles. Research on maize drought tolerance has identified key genetic mechanisms and QTLs, which are now integrated into breeding programmes. Marker-assisted selection (MAS) and studies on the nuclear factor Y (NF-Y) B subunit aim to improve sorghum feed quality and drought resilience. Comparative genetic mapping between maize and sorghum has revealed duplicated chromosome segments, enabling cross-species insights. While progress is evident, substantial scope remains for enhancing drought tolerance through scenario-specific breeding, genetic modelling, and the exploitation of tropical diversity. These efforts aim to sustain agricultural productivity amid growing water scarcity.