Phenotyping Summer Dormancy in Tall Fescue: Establishment of a Surrogate Phenotype and a Dormancy Rating System in Humid Environments

Tall fescue [Lolium arundinaceum (Schreb.) Darbysh] is a cool-season perennial grass with two major types of germplasm, Continental and Mediterranean. Most Mediterranean germplasm exhibit summer dormancy even when conditions are favorable for growth. Phenotyping summer dormancy in the field is difficult and costly. The objectives of this study are to develop a low-cost surrogate phenotyping approach for summer dormancy. The environmental cues that trigger dormancy in the mother plant would act similarly on seed dormancy and germination and thus may be used as a surrogate phenotype. Germination tests were conducted under various combinations of photoperiod and temperature using two summer-dormant and two non-dormant checks in growth chamber conditions. Combinations of six temperatures (18, 20, 22, 28, 30, 32, and 34 degrees C) and five photoperiods (0:24, 12:12, 14:8, 16:8, and 24:0 h light/dark) were tested for their effect on germination. The data showed that temperature had a larger effect on germination than photoperiod, with higher temperatures reducing the germination of dormant but non-dormant checks. A total of 168 accessions were evaluated for dormancy in field conditions using a combined score of plant regrowth height and senescence based on digital image analysis. Twenty six putative non-dormant and 30 dormant accessions were selected for seed germination testing to establish a correlation between seed germination and field dormancy. The data showed that the ratio of seed germination at 30 degrees C relative to 20 degrees C under the 24 h light photoperiod correlates well (r = 0.7) with field dormancy phenotypes and has potential to be used as proxy for phenotyping summer dormancy in tall fescue.