Résumé
Background: Rapidly increasing forage requirements of West African production systems prompted sorghum breeding programs to develop dual-purpose varieties that produce grain for food and fodder as a feed. Recessive alleles of two genes are known to improve sorghum forage value by reducing stem lignin content: the Dry gene (D) which controls stem juiciness and the brown midrib gene (bmr-12). This work evaluates the effects of introgression of these two alleles in Kalla Kéné, a photoperiod-sensitive variety from Mali with dry stem and white midrib. Material and method: three near-isogenic lines (ISOJ, ISOB, and ISOJB) were developed from five successive backcrosses between the recurrent parent Kalla Kéné and Redlan (bmr-12) a bmr juicy sorghum as donor parent. Line ISOJ has juicy allele, ISOB the brown midrib and ISOJB both alleles (juicy stem and brown midrib). Stem quality of the isogenic lines was studied in interaction with sowing dates using a split-plot design repeated over three years. Measurements were focused on phenology, morphology and stem chemical composition. Results and discussion: Genotype and sowing date effects are highly significant. Genotype x sowing date interaction is not significant. Delay in sowing leads to a decrease in lignin content, a later maturity, followed by a highly reduced biomass production. Lines with bmr-12 trait have a more strongly reduced lignin content compared to the one with only juicy allele. For all sowing dates, the decrease in lignin content does not lead to lodging. Conclusion: bmr trait is the best way to improve forage quality of photoperiod-sensitive sorghums. Innovative dual-purpose varieties will help develop value chains around fodder production. This result will have a positive impact on farmers' incomes, especially around urban centers where fodder deficits are a brake on livestock intensive farming. Conversion of malian elite sorghum varieties to bmr lines is underway.