Effects of drought on O-2 evolution and stomatal conductance of beans at the pollination stage

The predawn leaf water potential (Psi(1)), O-2 evolution (Ac) and stomatal conductance (g(s)) of three bean genotypes growing in a greenhouse were eva luated in order to compare the effect of water stress induced at different ages, especially during reproductive ontogeny. There was a peak of Ac for a ll genotypes 30 days after sowing (DAS) at the pollination stage, and the g reatest effects of drought on this parameter occurred at this stage, with a decline in Ac from a higher Psi(1), (- 0.35 MPa) than at the other stages (below - 1.0 MPa). The Psi(1), and final yield were also more reduced when drought was imposed at the pollination and flowering stages than at the veg etative or pod filling stages. During water stress, the g(s), of the genoty pes was reduced by drought, but Ouro negro showed a different behavior in i ts stomatal control under drought. Firstly, with water deficit imposition, it maintained a higher g, level in the morning (9:00 h), when the vapor pre ssure deficit is the lowest of the day, than at midday (12:00 h) and in the afternoon (15:00 h). Secondly, after rehydration, this genotype had a high er g, than non stressed plants. (C) 1999 Elsevier Science B.V. All rights r eserved.