The Concepts of Seed Germination Rate and Germinability: A Re-Evaluation for Cool-Season Grasses

Temperature is one the most influential environmental factors for the germination and establishment of grass species. The specific objective of this study was to determine the effects of low constant temperature on the time needed to express the full germination capacity of nondormant seedlots. Fifteen accessions, comprising seven of Lolium perenne L., three of Festuca arundinacea Schreb., three of Dactylis glomerata L. and two of Triticum aestivum L., were evaluated at constant temperatures of 5 and 21 degrees C. As expected, the germination rates were faster at 21 degrees C than at 5 degrees C. Indeed, at 5 degrees C seeds needed up to twenty-one times longer to reach the maximum germination than when tested at 21 degrees C. The genotypic variability found for the ratio of germination rates between the two temperatures (i.e., germination rate at 5 degrees C/germination rate at 21 degrees C) was much more variable than what is found in the literature for perennial cool-season grasses. On the other hand, in most cases, no significant differences were observed in the germinability (the capacity to germinate) response to 5 degrees C and 21 degrees C. Within the four species, twelve of the fifteen studied accessions expressed the same germinability at 5 degrees C and 21 degrees C, when given enough time. Only three accessions had final germination percentages higher at 21 degrees C than at 5 degrees C. Our results suggest that, in general, nondormant seeds at low temperatures germinate as well as nondormant seeds at near-optimal temperatures, provided they have enough time to express their germination capacity. These findings cast doubts on the validity of conclusions drawn in many studies where germination experiments were performed for a period insufficient to obtain full germination at low temperatures. Another major finding in this work concerns the risk of wrongly estimating germinability at low temperatures.