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 (C) and temperature (T) can describe these features of seed behaviour. We used the hydrothermal time model to analyse the effects of dormancybreaking treatments on germination of dormant true (botanical) potato (Solanum tuberosum L.) seeds (TPS). After-ripening (378C 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 [Cb(50)] decreased from 20.25 MPa in control seeds to 20.87 MPa and 21.83 MPa after 7 and 30 days of after-ripening, respectively. In contrast, the base temperature for germination (Tb) was relatively unaffected (0–3.38C). Fluridone (50mM), an inhibitor of abscisic acid (ABA) biosynthesis, also promoted germination of dormant TPS and lowered Cb(50), indicating a role for de novo synthesis of ABA during dormancy maintenance. Moist chilling (3 days at 48C) or gibberellin (100mM) alleviated secondary dormancy and lowered Cb(50) values from 20.08 MPa to 20.36 and 20.87 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.