Résumé
Sorghum offers the opportunity to produce grains and stem sugar in West African drought prone environments. This study investigated to which extent plant green leaf area dynamics, as affected by sowing date and post-flowering water availability, influences sugar accumulation in sweet sorghum stem. A field trial was conducted at CNRA of Bambey (Senegal). Twelve photoperiod-sensitive genotypes with contrasted morphology but similar phenology were grown during the rainy season 2013 using two sowing dates (July and August) and two post-flowering water regimes (stressed and well-watered). Leaf appearance, area and senescence were weekly measured. Panicle, stem dry weights and stem sugar content were measured at anthesis and maturity. Late sowing shortened the vegetative phase and accordingly the number of appeared leaves, with various extents depending on genotype. Leaf appearance rate was increased by late sowing, but individual leaf area was not. Accordingly, plant green leaf area was almost doubled at flowering with early sowing. It significantly correlated with stem biomass and sugar content (both R²=0.5) at anthesis. Panicle dry weight at maturity was significantly correlated with plant green leaf area at anthesis. Grain weight per panicle was significantly affected by sowing date but not by water stress. Sugar content at maturity was significantly higher and less affected by water stress in early compared to late sowing. Only genotypes with large plant green leaf area at anthesis, maintaining about 50% of green leaves until dough stage maintained sugar content under stressed condition. The benefits of early sowing and large green leaf area to minimize water stress effect and combine sugar and grain production is highlighted. (Texte intégral)