Hydrothermal time analysis of seed dormancy in true (botanical) potato seeds

As seed dormancy is released within a seed population, both the rate and percentage of germination increase progressively with increasing dose of a dormancy-breaking treatment or condition. Population-based models can account for this behaviour on the basis of shifting response thresholds as dormancy is alleviated. In particular, hydrothermal time analysis of germination sensitivity to water potential (Psi) and temperature (T) can describe these features of seed behaviour. We used the hydrothermal time model to analyse the effects of dormancy-breaking treatments on germination of dormant true (botanical) potato (Solanum tuberosum L.) seeds (TPS). After-ripening (37 degrees C and 4% seed moisture content) of TPS for 7 or 30 days partially or fully alleviated primary dormancy. The median base water potential required to prevent germination [Psi(b)(50)] decreased from -0.25 MPa in control seeds to -0.87 MPa and -1.83 MPa after 7 and 30 days of after-ripening, respectively. In contrast, the base temperature for germination (T-b) was relatively unaffected (0-3.3 degrees C). Fluridone (50 mu M), an inhibitor of abscisic acid (ABA) biosynthesis, also promoted germination of dormant TPS and lowered Psi(b)(50), indicating a role for de novo synthesis of ABA during dormancy maintenance. Moist chilling (3 days at 4 degrees C) or gibberellin (100 mu M) alleviated secondary dormancy and lowered Psi(b)(50) values from -0.08 MPa to -0.36 and -0.87 MPa, respectively. The hydrothermal time model allows quantification of dormancy levels and explains why changes in germination speed and percentage are closely correlated during dormancy alleviation.