Graduate Thesis Or Dissertation
 

Temperature preconditioning of ryegrass (Lolium sp.) seed dormancy

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  • The purposes of this study were to determine the effects of temperature, nutrients, growth regulators, and culm detachment during seed development on ryegrass seed dormancy and weight. The effects of storage temperature on seed dormancy were also studied. Seed dormancy of annual (Lolium multiflorum Lam.) and perennial (Lolium perenne L.) ryegrass was evaluated by observing germination in the dark at 30, 25, 20, 15, and 15-25C. Dormant ryegrass seeds failed to germinate at 30 and 25C, but as after-ripening occurred seeds became insensitive to germination temperature. Field-grown ryegrass varieties were found to differ in degree of seed dormancy when grown under the same environment. 'Gulf', 'Florida Rust Resistant', and 'Magnolia' annual and 'NK- 100', 'Manhattan', 'Atempo', 'Petra', and 'Pelo' perennial ryegrass varieties were considered dormant. 'Oobahikari' annual and 'Verna Pajbjerg' and 'Linn' perennial ryegrass varieties were nearly nondormant. Dormancy patterns of greenhouse-grown Manhattan perennial ryegrass seed differed from those of field grown Gulf annual ryegrass. Dormancy of Manhattan was reduced when seeds reached maximum dry weight; whereas, Gulf seeds were dormant at all stages of maturity. A detached culm technique was used in growth chamber and greenhouse studies to determine the effects of nutrients, growth regulators and temperature on seed weight and dormancy. 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 the detached culm technique in studying seed dormancy. Development of Gulf seed in solutions deficient in nitrogen, phosphorus, and potassium did not significantly reduce dormancy. Phosphorus deficiency was more detrimental to seed weight than deficiencies of nitrogen or potassium. Production of Gulf seed on detached culms in gibberellic acid, benzyladenine and sucrose reduced dormancy. Seed developed in sucrose on culms cut at the soil surface produced the largest seeds. However, these seeds were not equal in size to seeds from intact culms. Gibberellic acid had no effect on seed size, while benzyladenine solution significantly reduced seed weight. Ryegrass seed dormancy and weight were affected by temperature during seed development. Gulf seeds developed at low temperature were dormant; whereas, seeds developed at high temperature 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 one week of low temperature during the ripening stage increased seed dormancy, while the same duration of exposure to high temperature immediately after anthesis reduced seed dormancy. Extended periods of low temperature during seed development increased seed weight, while seed weight was decreased if low temperature preconditioning was delayed until later stages of development. The greatest reduction in seed weight occurred when seeds were exposed to high temperatures during the second week of seed development. In storage studies with seven ryegrass varieties, dormancy was quickly overcome at storage temperatures of 30 and 20C, but storage at 5 and -18C increased dormancy.
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