The first event in the germination sequence is imbibition. Water uptake limitation has an effect on germination velocity, decreasing or stopping this process. In water stress conditions seeds with different sizes may present different behaviour. The purpose of this study was to evaluate the effects of hydric stress induced by mannitol on the physiological seed quality of soybean cultivar 'IAC-18' classified by size in the 12 and 13 mesh and cultivar 'IAC-22' classified in the 12, 13 and 14 mesh. Seeds were sown on paper soaked in mannitol solutions at different concentrations (0; 44.58; 89.17; 133.75g L-1 distilled water) which produced the water potentials of 0, -0.6, -1.2 and -1.8MPa. Treatments were evaluated according the following characteristics: germination, first germination counting, seedling vigour classification, hypocotil and root length and shoot and root dry biomass. The experiment was conducted as a completely randomized design with the treatments in a factorial scheme of 2x4 and 3x4 (seed size x mannitol concentration) for each cultivar, respectively. Results showed that calculated water potential at -0.52 and -0.49MPa promoted maximum germination for the smallest and largest seeds, respectively. For 'IAC-22' cultivar the calculated water potential of -0.514, -0.51 and -0.46MPa induced maximum germination for the seeds of 12, 13 and 14 mesh, respectively. Up to the water potential of -1.27 and -1.04MPa the largest seeds produced the highest germination percentage for 'IAC-18' and 'IAC22' cultivars, respectively. Germination was less affected than the evaluations of seedling development at the different levels of water potential, and these characteristics decreased with the increase in water stress.
Glycine max; water stress; mesh; seed classification
