Water relationships and high temperatures in “Flor de Mayo” type beans

Abstract

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^-1 Nitrogen and 40 kg.ha^-1 Phosphorous were used. Leaf water (Ψ=-0.33 Mpa), osmotic (π=-1.26 mpa) and turgor (P=0.93 Mpa) potentials at mI were higher than at CRF (Ψ= - 0.77, π=-1.36 y P=0.59 Mpa) and MRF (Ψ=-1.22, π=-1.57 y P=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 and at MRF. The high CT also had a significant effect in the FABMand SY, and its components; high CT reduced SY, FABM, number of normal pods.m^-2 (NP. m^-2) and weight of 100 seeds (W100S) by 12.5, 10.7, 10.2 y 3.4% for each ºC (^-1 ºC) increase in CT, respectively.