The temperature and length for the release of primary and induction of secondary physiological dormancy in Korean pine (Pinus koraiensis Sieb. et Zucc.) seeds

Abstract

Primary physiological dormancy and secondary physiological dormancy of Korean pine seeds restrict the regeneration of broad-leaved Korean pine (Pinus koraiensis) mixed forest. Dry and imbibed seeds were stratified at 1 °C and 5 °C for 1, 2, 4 and 6 months. Germination percentage, mean germination time (MGT) and germination rate index (GRI) were measured to determine the optimal low temperature and its duration for the release of primary physiological dormancy. Once primary physiological dormancy was released through cold stratification, seeds were stored in an environment in which the temperature progressively increased from 5 to 25 °C. After one month of storage at each storage temperature, the germination percentage, MGT and GRI were measured to determine the threshold temperature for the induction of secondary physiological dormancy. Both dry and imbibed seeds not only exhibited a high germination percentage (approximately 80%) but also germinated rapidly (MGT and GRI were 17 days and 2.36, respectively) after 6 months of storage at either 1 °C or 5 °C. The germination percentage of cold stratified seeds gradually decreased from 78% (5 °C) to 72% (10 °C), 55% (15 °C), 10% (20 °C) and 8% (25 °C). The results of this study suggest that stratifying seeds at 1 °C or 5 °C for 6 months releases primary physiological dormancy. The induction of secondary physiological dormancy occurs at temperatures above 15 °C.