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Effect of Temparature Preconditioning and Cultivar on Ryegrass (Lolium sp.) Seed Dormancy¹

This study was conducted to determine if cultivar differences in seed dormancy existed in ryegrass (Lolium sp.), and whether seasonal differences in dormancy could be related to temperature during the seed development period.

Field-grown ryegrass cultivars differed in degree of seed dormancy when grown under the same field environment. ‘Gulf,’ ‘Florida Rust-Resistant,’ and ‘Magnolia’ annual and ‘NK-100,’ ‘Manhattan,’ ‘Atempo,’ ‘Petra,’ and ‘Pelo’ perennial ryegrass cultivars were considered dormant. ‘Obahikari’ annual and ‘Verna Pajdjerg’ and ‘Linn’ perennial ryegrass cultivars were nearly nondormant.

Temperature preconditioning during seed development and maturation affected the degree of dormany present in freshly harvested seed. These studies were conducted using a detached culm technique in growth chamber and greenhouse facilities. The dormancy response of Gulf seed produced on detached culms was similar to that of seeds from intact plants, lending validity to the use of this technique. Gulf seeds developed at low temperatures were dormant, but those developed at high temperatures were nondormant. The duration of exposure to different temperatures and the stage of development at which the seeds were exposed to high or low temperature also influenced the degree of dormancy. Exposure to 1 week of low temperature during ripening increased seed dormancy, but at anthesis reduced dormancy. Extended periods of low temperature during seed development increased seed weight. Seed weight was reduced when seeds were exposed to high temperatures during the 2nd week of seed development.

A multi-temperature technique was used to characterize the degree of dormancy present in the seeds.

Key Words: Environment • Germination

² Assistant Professor of Agronomy, Montana State University (formerly graduate research assistant, Department of Agronomic Crop Science, Oregon State University), and Professor of Agronomy, Department of Agronomic Crop Science, Oregon State University, Corvallis, Ore. 97331.

Received for publication March 23, 1972.