Résumé
Sorghum offers the opportunity ta combine grain and stem sugar production in West-African drought prone environments. This study investigated to which extent plant green leaf area dynamics and its regulation 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 (dry-down and wellwatered). Leaf appearance, area and senescence were weekly measured on the main stem as tillering was negligible. Panicle, stem dry weight and stem sugar content were measured at anthesis and maturity. August sowing shortened the vegetative phase and accordingly the number of appeared leaves, with various extents depending on the genotype. It increased leaf appearance rate but did not modify individual leaf area. Accordingly, plant green leaf area was almost doubled at flowering with July sowing. It was significantly correlated with stem biomass and sugar content (bath R2=0.5) at anthesis and with panicle dry weight at maturity. Grain dry weight per panicle was significantly affected by sowing date and water treatment. Stem sugar content at maturity was significantly higher and less affected by water stress in July compared to August sowing. Only genotypes with large plant green leaf area at anthesis, and maintaining about 50% of green leaves until dough grain 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. (Résumé d'auteur)