Photosynthesis and Yield Responses of Morphologically Distinct Pisum sativum L. Varieties to Terminal Drought

Drought limits pea (Pisum sativum L.) productivity by reducing growth, photosynthesis, and reproductive success, yet comparative field data across contrasting canopy morphologies are scarce. This study evaluated five pea varieties—Alejandrita (short-climbing), San Isidro and Santa Isabel (tall-climbing), and two afila varieties (Afila, Rizada)—grown under plastic crop covers and subjected to terminal drought (irrigation withheld from flowering) or a fully irrigated control. This study measured photosynthetic variables, including gas exchange and chlorophyll fluorescence; predawn and midday leaf water potential; dry mass and yield components; and calculated intrinsic and irrigation water-use efficiencies. Terminal drought reduced canopy biomass and yield in all varieties, with stronger canopy-level effects than branch-level effects. Varietal responses diverged: Afila and San Isidro maintained higher intrinsic water-use efficiency and biomass yield and exhibited conservative reductions in CO2 assimilation; by contrast, Santa Isabel and Alejandrita showed earlier declines in leaf water potential and greater susceptibility to yield loss. Results indicate that drought tolerance was not determined solely by variety type; rather, leaf-level intrinsic water-use efficiency, the timing of water-potential decline, and reproductive resilience underpin varietal differences. These traits are promising targets for breeding, and, based on these results, afila varieties and San Isidro showed promising performance and merit further evaluation in multi-environment trials.