Physiological responses of different soybean cultivars to soil water stress

The objective of this work was to determine possible varietal differences in some physiological parameters and their relation with seed production. The cultivars used were: Forrest, Asgrow 5308, Federada I INTA, Pelotas 8549 and Pelotas 8576. The treatments were three periods of water stress (in R2, R3 and R6) until 60% of equivalent humidity (EH) and the controls to EH. Tanspiration rates were lower in the two Pelotas cultivars among water levels and in the first two periods of water stress, with both cultivars showing the greatest pilosity. The foliar water potentials (psi f), stomatal conductancies and foliar temperatures were not different among cultivars within water levels in the first two periods of water stress. Seed production under EH decreased as follow: 'Asgrow 5308', 'Federada I INTA', 'Forrest', 'Pelotas 8576' and 'Pelotas 8549'. The psi f was the best indicator of the effects of water stress on seed yield. The water stress increased the number of poorly developed seeds, but the ones which completed their normal size showed better physiological quality than those produced under irrigation conditions.