|Abstract or Summary
- 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
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
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.