Hydrotime analysis for determination of seed vigour in cotton

This research was conducted to test whether hydrotime parameters are related to germination, emergence and early seedling vigour in cotton with the aim of determining whether hydrotime analysis might be used as a vigour test. Three experiments were carried out: (1) a germination test to obtain hydrotime parameters; (2) a laboratory seedling growth experiment; and (3) a greenhouse experiment. Relationships were examined between hydrotime parameters and early growth parameters obtained from the laboratory and greenhouse experiments, for each of three water potentials separately and for the overall mean. Results showed that there was wide variation among lots for hydrotime and early growth parameters. The hydrotime constant for germination, theta(H), ranged from 14.7 to 105.5 MPa-hours. The median base water potential, psi(b)(50), varied from -1.15 to -0.48 MPa and sigma(psi b) ranged from 0.23 to 0.72. There was no relation between theta(H) or sigma(psi b) and seedling emergence percentage. Therefore, they cannot be applied as a seed vigour test in cotton. The psi(b)(50) was the sole parameter acceptable for predicting emergence potential of cotton seed lots. Seed vigour of cotton can be classified based on psi(b)(50) as low (psi(b)(50) > -0.689MPa), intermediate (psi(b)(50) -0.689 to -0.815MPa) and high (psi(b)(50) < -0.815MPa).