10th U6+ Consortium of African Universities International Conference

Twin constraints of recurrent drought and phosphorus (P)-deficient soils slash upland rice yields across smallholder farming systems in sub-Saharan Africa, yet no study has characterised Kenyan germplasm for combined drought-phosphorus stress tolerance. We screened 96 upland rice genotypes using a citizen-science phenotyping framework that bridges precision laboratory methods with indigenous seed knowledge, the first combined-stress phenotyping effort in Kenyan upland rice. Polyethylene glycol (PEG-6000 at 20%) imposed osmotic stress in a completely randomized design with three replications, producing a 107-percentage-point spread in root length reduction (stress tolerance index: −9.21% to 97.91%; CV = 18.3%). We advanced 25 elite drought-tolerant accessions into hydroponic paper-pouch assays under contrasting phosphorus regimes: low P (LP: 0.009 mmol/L KH₂PO₄) versus normal P (NP: 0.18 mmol/L KH₂PO₄). Under PEG stress, UOE 44 (−9.21%), UOE 285 (29.36%), and UOE 298 (33.33%) maximised root elongation, signalling stress-activated auxin-driven foraging. Under LP, UOE 269, UOE 288, and UOE 285 maintained primary root length within ≤0.2 cm reduction, reflecting high phosphorus-acquisition efficiency, whereas UOE 275 and UOE 57 lost >3.0 cm, marking acute P sensitivity. Root maximum length functions as a low-cost, farmer-deployable phenotypic proxy connecting laboratory screening to participatory varietal selection, a scalable citizen science model for nutrient-limited smallholder systems in Kenya. UOE 44, UOE 269, and UOE 285 outperformed all screened accessions under both stresses and now enter greenhouse phenotyping and marker-assisted selection to fast-track climate-resilient, low-input upland rice varieties for deployment in Kenya.