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The water relations of seed pretreatments and their effects on the germination of radiata pine seeds


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Donovan, Nadine 2001 , 'The water relations of seed pretreatments and their effects on the germination of radiata pine seeds', PhD thesis, University of Tasmania.

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Seeds sown in Pinus radiata D. Don (radiata pine, Monterey pine) nurseries are
generally the culmination of generations of breeding and selection. Seed germination
characteristics have no generally been of high significance to the breeding programme
and seedling emergence from valuable seeds is often low and variable. Seed
pretreatrnents are sometimes used in an attempt to overcome variation in seed quality
and to achieve best possible germination.
The present study investigated commonly used seed pretreatments and their effect on
the germination of Pinus radiata seeds in laboratory, glasshouse and field conditions.
Current nursery practice is to soak seeds at or near room temperature prior to sowing.
In this study it was found that soaking decreased the time to emergence in the
laboratory and field but damage occurred to some seedlots when soaked. Dissolved
oxygen in soak water was depleted rapidly during soaking and damage was prevented
when soak water was aerated throughout soaking. Stratification (moist chilling) was once widely used to pretreat radiata pine seeds in
Australia, but use of the practice has declined recently. Twelve weeks of stratification
at 5 ° C decreased the time to emergence in the laboratory by up to 12 days. This effect
decreased with shorter duration of stratification. After 12 weeks of treatment seeds
began to germinate at low temperature and were susceptible to damage and desiccation
during sowing.
A third pretreatment not presently in commercial use examined the effect of stratifying
while controlling seed water potential. A treatment was developed that enabled seeds to
attain the benefits of stratification without risking damage. This was achieved by
limiting the moisture available during treatment, by controlling the relative humidity of
the environment in which the seeds were chilled. The treatment was as effective as
conventional stratification in overcoming barriers to rapid germination. The seeds were
fully hydrated by 4 weeks of treatment, but extending the treatment to 12 weeks further
improved germination. This suggests that processes occur in fully hydrated seeds held
at low temperature which overcome barriers to germination.
In view of the interrelationship between metabolic activity and water uptake, aspects of
water relations and gas exchange were investigated in more detail. An examination of
seed water relations during imbibition at 200 C revealed that the embryo was
apparently fully hydrated within 24 hours. Water potential of intact seeds rose to near
-8 MPa within 24 hours. Final water potential achieved 6 days later before splitting and
germination was also -8 MPa. After initial water uptake there appears to have been a
readjustment of both water content and seed water potential over the next 4 days, as
both declined following the rapid initial rise. The decline was also associated with
increasing respiration, which suggests there may be active movement of water out of
the seed after imbibition. After this period of readjustment potential increased rapidly
up until embryo expansion and radicle emergence. During the period of readjustment
of seed water potential there remained a potential difference of 7 -8 MPa between the
extracted embryos and the remainder of the seed, in spite of available free water. Results are discussed in terms of the physiology of water uptake and seedling
emergence and practical implications of commercial management of high value P.
radiata seeds.

Item Type: Thesis - PhD
Authors/Creators:Donovan, Nadine
Keywords: Pinus radiata, Germination, Seeds
Copyright Holders: The Author
Copyright Information:

Copyright 2001 the Author - The University is continuing to endeavour to trace the copyright
owner(s) and in the meantime this item has been reproduced here in good faith. We
would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2001. Includes bibliographical references

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