Hydrotime (θH) models provide information on seed tolerance to low water

potential and time to germination under different conditions. Here it was evaluated the

capacity of graphic and probit model to describe germination parameters and germination

times (t) in a tropical legume (Peltophorum dubium). Germination tests were conducted

under reduced water potentials (polyethylene glycol solutions from 0 to -1.2 MPa) at 25

°C. Regression lines were applied to investigate the relationship between germination

rates (1/t) and water potential for different germination percentages (fractions 10, 30, 50

and 70%). Those regressions were used in the graphic model to calculate θH (1/slope) and

determine the base water potential (Ψb) as the point which the line intercepts the x-axis

(G% = 0). In the probit model, germination percentages were transformed to probit units

and plotted against Ψb-values to describe germination response under a single regression

line. Values for θH varied from 1.8 to 2.0 MPa day in both models, and Ψb showed a normal

distribution, as presupposed by the probit model. Predicted germination times (t10 and

t50) mostly fell within observed times, thus showing biological relevance of the models to

describe the effects of water potential on seed germination.