Genotypic Variation for Root Development, WaterExtraction and Yield Components in Groundnut Under LowPhosphorus and Drought Stresses

[Context] Unpredictable water deficit (drought) and low soil phosphorus (LP) are major interacting constraints to groundnut growth and grain yield in Sahelian zones of West Africa. Combining breeding efforts for drought tolerance and P efficiency could lead to improve tolerance and grains yield in these zones. [Objectives] This study assessed six groundnut genotypes under lysimetric system to better understand the relative importance of P deficiency, water stress, and their interaction; investigate the water extraction pattern of genotypes under these constraints and identify tolerance related traits to accelerate development of more resilient varieties. [Methods] Thus, in experiment 1 (Exp.1) roots traits were investigated at 50% flowering, pod filling stage (60 days after sowing) and maturity stage (90 days after sowing) under high phosphorus (HP) and LP treatments. In experiment 2 (Exp.2), two water regimes (WW=well water, and WS = water stress) were imposed to HP and LP plants and parameters like total transpired water (TTW), transpiration efficiency (TE), water extraction (Wex), pods and haulm heights were investigated. [Results] Roots traits showed significant decrease due to LP stress, pod and haulm weights correlated significantly to roots length density (RLD) and roots dry matter (RDM). Genotypes 12CS-116 and ICGV 12991 revealed tolerant to LP stress while RLD and RDM revealed LP tolerance related traits in groundnut. Interacting effect of LP and drought stress (LPWS) was higher than separate effect of LP and WS. Under LPWS, Wex, TTW, TE, pod and haulm yields decreased significantly. This study suggests that RLD and RDM contributed to Wex in 12CS-116 and ICG 12991 under LPWS. 55-437 and JL-24 with highest TTW showed drought tolerance strategy while drought avoidance strategy could explain 12CS-116, 12CS-79, ICG 12991 and ICGV 97183 response to WS. Pod weight showed tight correlation (R2 =0.7) to TE only under LPWS suggesting that TE explains a large part of pod yield variation under LPWS conditions. TE revealed WS and LPWS tolerance related trait. The genotypic variation observed on Wex and TTW under LPWS suggests different patterns of water extraction and use among the groundnut genotypes.