Soil water deficit and high air temperature effects on plant water relations and canopy temperature (CT), and seed yield (SY) and its components in 8 “Flor de Mayo” (FM) bean varieties and a landrace were studied. Three experiments were carried on under field conditions; Montecillo irrigation (MI) with watering from sowing to maturity, Montecillo rain-fed (MRF) with rainfall as the only source of water and Celaya rain-fed (CRF) with rainfall + 2 supplementary waterings at flowering. Rates of 80 kg.ha<span name="style_sup">-1</span> Nitrogen and 40 kg.ha<span name="style_sup">-1</span> Phosphorous were used. Leaf water (ψ=-0.33 Mpa), osmotic (π=-1.26 Mpa) and turgor (<span name="style_italic">P</span>=0.93 Mpa) potentials at MI were higher than at CRF (ψ=-0.77, π=-1.36 y <span name="style_italic">P</span>=0.59 Mpa) and MRF (ψ=-1.22, π=-1.57 y <span name="style_italic">P</span>=0.35 Mpa); MRF with a greater soil water deficit, showed greater reduction in ψ and π and higher capacity for osmotic adjustment (OA). OA was positive and significantly related to seed yield (SY) and final aerial biomass (FABM) in the 2 rain-fed environments. Canopy temperature (CT) at MI (26.7°C) was lower than at CRF (30.8°C) and MRF (36.6°C); the heat stress effect increased with the drop in plant water content in the driest environment (MRF); CT was negative and significantly associated with ψ and π at MRF. The high CT also had a significant effect in the FABM and SY, and its components; high CT reduced SY, FABM, number of normal pods.m<span name="style_sup">-2</span> (NP.m<span name="style_sup">-2</span>) and weight of 100 seeds (W100S) by 12.5, 10.7, 10.2 y 3.4% for each ºC (<span name="style_sup">-1</span>ºC) increase in CT, respectively.ºC) increase in CT, respectively.

water; osmotic and turgor potentials; osmotic adjustment; heat; canopy temperature; irrigation; rainfed