A Method to Differentiate Summer-Dormant from Summer-Active Cool-Season Grasses at Germination Stage.

The acreage sown to summer-dormant, cool-season perennial grasses is increasing in regions where climatic conditions resemble those of the Mediterranean Basin.  Because of the environmental challenges associated with climate change and the need for resilient perennial grasses, we sought a simple method to differentiate summer-dormant from summer-active types of cool-season grass accessions. Such a method would reduce the time needed to generate breeding lines rather than the time-consuming and uncertain conditions associated with traditional controlled environment and field experiment techniques. We developed a method based on germination responses to photoperiod to differentiate summer-dormant from summer-active types of tall fescue [Lolium arundinaceum (Schreb.) S.J. Darbyshire] and orchardgrass (Dactylis glomerata L.). Seed of cultivars with known summer dormancy characteristics was germinated at constant temperature of 24^o C under a range of photoperiods (0-24 h) for 14 d. Total germination, modeled cumulative germination, instantaneous rate of germination, and relative germination (to that in the dark) was analyzed. Germination of summer-dormant orchardgrass was similar in the dark and short photoperiods (4-12 h), but it was inhibited by photoperiod longer than 12 h. Germination of summer-active orchardgrass was promoted by any photoperiod when compared with control (0 h). Short photoperiods (4-12 h) promoted while long photoperiod (> 12 h) inhibited germination of summer-dormant tall fescue. Summer-active types of tall fescue did not respond to photoperiod, regardless of length. A validation test using experimental lines of Mediterranean-origin tall fescue with known expression of summer dormancy characteristics confirmed the accuracy of our method.