Use of model assisted yield frameworks for the analysis of cotton varietal response to drought

Three experiments were conducted under field conditions in Senegal to study the effects of a post-floral drought on seed-cotton yield and yield components of five cotton cultivars. The fraction of transpirable soil water (FTSW) was used to characterize the soil water deficit as experienced by the plants in each elementary plot. Two model-assisted frameworks of analysis of the seed-cotton yield were used : (1 ) number of bolls and average boll weight, associated with a leaf and flower development model; (2) total aerial biomass produced and harvest index, associated with a light interception model. The effects of irrigation treatments on seed-cotton yield varied from year to year, as rainfall pattem in the pre-flowering period differed. The overall variation in yield between years and experiments was accounted for by the average FTSW during the reproductive period and by the duration of this period. Water deficit induced an earlier termination of plant development (cutout, when NAWF=5) that reduced the effective flowering period and the number of fruiting sites produced. A reduction of the average boll weight was also observed under terminal drought conditions. Water deficit induced an overall reduction in leaf area index and radiation interception that largely accounted for the effects of water deficit on total aerial biomass production. Duration of the flowering period and harvest index were the most effficient variables to explain genotypic differences in yield under the various conditions of water supply. The two frameworks of analysis of the seed-cotton yield, and the associated phenology and growth models, allowed a common analysis of piant responses to drought as observed under the various years, irrigation conditions, and for the various genotypes. (Résumé d'auteur)