A stratification thermal time-based model as a tool for designing efficient methodologies to overcome seed dormancy constraints to kiwifruit seedling production

Abstract

Kiwifruit (Actinidia deliciosa A. Chev. C.F. Liang and A.R. Ferguson) seedling production in the nursery is usually impaired because of low seed germination resulting from primary dormancy. Dormancy of hydrated seeds is alleviated by the perception of a period at low temperatures (stratification), but further incubation under fluctuating temperatures (20/30 °C) is a requirement for dormancy termination. The aim of this study was to establish functional relationships between changes in the sensitivity of the seed population to different cycle-doses of fluctuating temperature and dormancy alleviation under different times and stratification temperatures. We propose a model based on the concept of stratification thermal time to predict changes in the fraction of the seed population that would germinate as a function of the number of fluctuating temperature cycle-doses. Results showed that stratification at cool temperatures produced higher rates of change than stratification at warmer temperatures. Construction of response curves with a thermal time scale was possible because seeds that had accumulated similar stratification thermal time achieved similar germination percentages in response to cycle-doses of fluctuating temperatures. The model was tested against independent experimental data yielding good agreement between predicted and observed data. Overall, this constitutes an important tool to overcome dormancy in a way that should result in a more efficient and faster production of kiwifruit seedlings or rootstocks.