A predictive model for dormancy loss in Polygonum aviculare L. seeds based on changes in population hydrotime parameters

Changes in population hydrotime parameters were determined during stratification in Polygonum aviculare L. seeds in order to model dormancy loss. Seeds buried in pots were stored at three temperatures (1.6, 7 and 12degreesC) for 110 d and were exhumed at regular intervals during the storage period. Exhumed seeds were incubated at different water potentials at 15degreesC and germination time courses were analysed to determine hydrotime parameters. The population mean base water potential (Psi(b)(50)) decreased concomitantly with seed dormancy, while the hydrotime constant (theta(H)) and the standard deviation of base water potential (sigma(Psib)) displayed only minor changes. Based on these results, a model for simulating P. aviculare seed dormancy loss in relation to low temperature was developed. The model employs Psi(b)(50) as an index of mean seed population dormancy status. While Psi(b)(50) was allowed to vary as seeds were released from dormancy, theta(H) and sigma(Psib) were held constant. Changes in Psi(b)(50) were related to the time and temperature, using a previously developed thermal stratification time index (S-tt), which quantifies the accumulation of thermal time units below a threshold temperature required for dormancy loss to occur. Therefore, Psi(b)(50) varied in relation to the accumulation of S-tt according to time and temperature. Model performance showed acceptable prediction of timing and percentage of germination of seeds buried in irrigated plots, but did not accurately predict germination of seeds exhumed from rain-fed plots. Thus, environmental factors other than temperature could also be involved in the regulation of dormancy status of buried seeds under field conditions.