Evaluation of photoinhibition and development of stress tolerance index to identify photosynthetically adapted and stress tolerant germplasm accessions of tepary bean.

Knowledge about photosynthetic adaptation and stress tolerance in tepary bean (Phaseolus acutifolius) accessions under acidic soil and high‑temperature conditions in the Colombian Amazon is limited. We developed a stress tolerance index (STI) as a helpful scorecard based on physiological measurements of 323 accessions that were grown in acidic soil under field and screenhouse conditions and were evaluated under well‑watered and water‑stressed treatments at dawn and midday. Based on STI and complementary photosynthetic traits, accessions were classified into five adaptive categories (highly: n = 34, 10.5%; moderately: n = 49, 15.1%; slightly: n = 79, 24.4%; poorly: n = 100, 30.9%; very poorly: n = 61, 18.8%). Three accessions (G40068, G40302, G40087) stood out in overall performance: G40087 had the highest STI (0.754), G40068 the highest Fv/Fm (0.737), and G40302 the highest qL (0.562). These accessions also exhibited higher relative chlorophyll content (between 45 and 52), greater leaf thickness (between 280 and 320 μm), a maximum photochemical efficiency of about 0.73, and an effective quantum yield of >0.45 under stress-traits that supported better photosynthetic performance. These materials could serve as promising parents for breeding climate‑resilient beans adaptive to the western Amazon, but their agronomic value requires validation in yield and biomass trials under the same stress conditions.