Dormancy release during hydrated storage in Lolium rigidum seeds is dependent on temperature, light quality, and hydration status

Abstract

The influence of temperature, light environment, and seed hydration on the rate of dormancy release in Lolium rigidum (annual ryegrass) seeds during hydrated storage (stratification) was investigated. In a series of experiments, seeds were subjected to a range of temperatures (nine between 5°C and 37°C), light (white, red, far-red, and dark), and hydration (4-70 g H 2O 100 g-1 FW) during stratification for up to 80 d. Samples were germinated periodically at 25/15°C or constant 15, 20, or 25°C with a 12 h photoperiod to determine dormancy status. Dark-stratification was an alternative, but not equivalent dormancy release mechanism to dry after-ripening in annual ryegrass seeds. Dormancy release during dark-stratification caused a gradual increase in sensitivity to light, but germination in darkness remained negligible. Germination, but not dormancy release, was greater under fluctuating diurnal temperatures than the respective mean temperatures delivered constantly. Dormancy release rate was a positive linear function of dark-stratification temperature above a base temperature for dormancy release of 6.9°C. Dormancy release at temperatures up to 30°C could be described in terms of thermal dark-stratification time, but the rate of dormancy release was slower at ≤15 °C (244°Cd/probit increase in germination) than ≥20 °C (208°Cd/probit). Stratification in red or white, but not far-red light, inhibited dormancy release, as did insufficient (<40 g H2O 100 g-1 FW) seed hydration. The influence of dark-stratification on dormancy status in annual ryegrass seeds is discussed in terms of a hypothetical increase in available membrane-bound phytochrome receptors.