Water stress responses of Saba senegalensis provenances during the seedling stage

Abstract

Saba senegalensis is a multi-purpose liana from sub-Saharan Africa that is under threat from over-exploitation of its fruits and from land degradation and erratic rainfall affecting its regeneration. This research aims to assess survival, growth and dry matter distribution in the responses to water regimes of S. senegalensis seedlings of nine provenances from slightly, moderately and severely dry zones in Burkina Faso. The study parameters were provenance, water regimes and duration of drought stress. A total of 567 seedlings (63 per provenance) were grown using a factorial design. Five months after germination, three water regimes were applied: high, medium and low soil water content, corresponding respectively to 100, 75 and 50% of soil pot capacity. The experiments lasted for 6, 9 and 12 months after water stress began. Survival rates, growth parameters, biomass production, stress tolerance and stress sensitivity indexes were calculated and the data analyzed using a linear mixed model. Drought stress reduced seedling survival and biomass production, while the relative growth rate in collar diameter increased. Concerning the duration of drought stress, the relative growth rate of seedlings in collar diameter decreased and the shoot-to-root ratio increased. After six months under stress, the seedlings had invested more in roots, whereas after nine and twelve months the reverse trend was observed. Furthermore, seedlings from the slightly dry zone produced more biomass when watered under a low soil water content regime, and were more drought-tolerant than those from severely and moderately dry zones. This could indicate that the seedlings originating from these zones are well adapted to growth under severe water stress. For S. senegalensis domestication programs, seedlings originating from the slightly dry zones can be successfully propagated in agroforestry systems where water is a limiting factor.