Résumé
Forage maize is a crucial component of dairy cow nutrition, with dry matter digestibility directly affecting milk production. While past research has shown that drought reduces plant yield, recent findings pinpoint the fact that digestibility is increased under drought. Yield losses can therefore be recuperated through increases in digestible yield. In this project, we investigated how water and heat stress influence hybrid forage maize digestible yield and identified the key factors modulating this response under varying stress intensities. Over two years, we grew a range of modern early forage maize hybrids under four controlled water stress regimes in fields in France, and performed agronomic, biochemical, and histological phenotyping. This multiscale approach enabled us to pinpoint the traits linked to digestibility changes. We also developed an integrated heat-water stress index to precisely quantify stress severity. Our findings reveal that while severe stress notably reduces ear production, dry matter digestibility can be maintained through improved cell wall digestibility. Regardless of stress intensity, increased cell wall digestibility is associated with decreased p-coumaric acid content and a redistribution of stem lignin, even as overall lignin content and structure remain stable. The role of lignin distribution becomes increasingly critical under more severe stress, significantly impacting digestibility variations. We suggest that breeding for stress-resilient digestibility focus on how p-coumaric acid content declines without changing total lignin levels. Furthermore, selection trials should include moderate stress conditions to better equip hybrids for future climates.