A method to differentiate summer-dormant from summer-active tall fescue and orchardgrass accessions at germination

Authors: MALINOWSKI, D - TEXAS A & M UNIVERSITY; Belesky, David; KRAMP, B - TEXAS A & M UNIVERSITY; Ruckle, Joyce; KIGEL, J - HEBREW UNIV JERUSALEM; PINCHAK, W - TEXAS A & M UNIVERSITY

Submitted to: Australian Journal of Agricultural Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2008
Publication Date: 12/15/2008
Citation: Malinowski, D.P., Belesky, D.P., Kramp, B.A., Ruckle, J.M., Kigel, J., Pinchak, W.E. 2008. A method to differentiate summer-dormant from summer-active tall fescue and orchardgrass accessions at germination. Australian Journal of Agricultural Research. 59:1092-1102.

Interpretive Summary: Changing trends in long-term weather patterns challenge traditional pasture production strategies. New forage plant resources are needed that can tolerate increased temperatures, and relatively lesser amounts of precipitation. One plant adaptation strategy is to prevent seedling exposure to these inhospitable growing conditions. Seed germination is governed by a number of environmental cues including temperature, and light quality and quantity. Seeds that avoid germinating during long days, such as those occurring in summer, are likely to encounter cooler temperatures and more favorable soil moisture conditions. Plants with this capability are likely to be summer dormant plants that would persist in hot, dry environments by avoiding exposure to excessive heat and drought, while remaining productive in the cooler portions of the year. We devised a simple test to identify the seeds of summer-dormant plants so that new plant resources with the ability to withstand extreme summer conditions can be developed. We found that the seeds of summer dormant tall fescue and orchardgrass plants were sensitive to daylength, whereas the seeds of summer active plants were not. This simple test enables plant breeders to identify summer-dormant lines of forage grasses easily and inexpensively without time-consuming procedures and uncertain weather conditions associated with field trials.

Technical Abstract: Summer-dormant, cool-season perennial grasses are being used in place of traditional, summer-active cultivars for high quality winter forage. One reason for this change is the ability of cultivars with summer-dormant attributes to tolerate increasing annual temperature, decreasing precipitation, and repeated severe summer droughts. The mechanism of summer dormancy is still not understood in detail. Cultivar development for summer dormancy typically is conducted under field conditions in environments where summer-active types do not survive summer weather conditions. 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 deg C under a range of photoperiods (0 – 24 h). The relative germination of summer-dormant tall fescue was greater at short photoperiods (< 12 h) and less at long photoperiods (> 12 h) when compared to germination in the dark. Summer-active types did not respond to photoperiod, regardless of length. Germination of summer-dormant orchardgrass was similar in the dark and short photoperiods, but less at longer photoperiod when compared with germination in the dark. Summer-active orchardgrass always had greater germination at any photoperiod longer than 0 h. A validation test using experimental accessions of Mediterranean-origin tall fescue with known expression of summer dormancy characteristics confirmed the accuracy of our method.