Moisture Determination in Nonorthodox Seed

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Moisture Determination in Non-orthodox Seed

• Craig McGill, Institute of Natural Resources,
  College of Sciences, Massey University, New
  Zealand

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What is non-orthodox seed?

• orthodox seed

• can be dried to 2-6 moisture (i.e. moisture
  content in equilibrium with 10-12 RH at 20C)

• negative logarithmic relationship between
  moisture content and seed longevity

• between -20C and 90C seed longevity at a
  constant moisture content increases as
  temperature decreases (Hong et al., 1998).

non-orthodox seed - low moisture contents are
lethal.
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What is non-orthodox seed?

• Non-orthodox seed can be divided into two
  categories

Recalcitrant

• can not be dried to below 15-20 moisture (i.e.
  moisture content in equilibrium with less than
  70 RH at 20C) without loss of viability, (Hong
  and Ellis, 1996)

• viability is often lost at higher moisture
  contents e.g. 23 for cocoa (Theobroma cacao),
  61.5 for mangrove (Avicennia marina)

• tropical species can be chilling sensitive and
  lose viability if stored at 5-15C (Hong et al.,
  1998).

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What is non-orthodox seed?
Intermediate

• will tolerate some drying, typically, to 10-12
  moisture (i.e. moisture content in equilibrium
  with 40-50 RH at 20C), (Hong et al., 1998)

• at lower moisture contents storage life is
  reduced

determination of desiccation tolerance does not
determine storage behaviour
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What is the purpose of moisture testing?

• Moisture tests have three main purposes

• preparation of seeds for both long and short
  term storage

• calculation of dry weight (determination of
  selling price)

• precursor for some vigour tests

ISTA Handbook on Moisture Determination
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Why are we interested in moisture determination
in non-orthodox seed?

• Many commercially important tree and shrub
  species show non-orthodox storage behaviour

• Hevea brasiliensis

• Castanea sativa

• Juglans nigra

Some are already in the ISTA Rules

• Acer pseudoplatanus

• Quercus alba, Quercus robur, Quercus rubra

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Moisture determination in non-orthodox seed.

• Problems

Surrounding structures may be difficult to
separate from the seed
Embryo axis may form only a small portion of the
seed
Moisture content of the embryo axis and storage
tissues may differ
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Nikau Rhopalostylis sapida
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R. sapida fruit and relative contribution by dry
weight of its components
Fruit layers including endocarp 39.0
Seed including endosperm and coat 60.6
Embryo 0.4
Radicle
(From Moore and Irwin, 1978)
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March 2004 CollectionGermination of R. sapida
fruits stored in moist vermiculite
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March 2004 CollectionGermination of R. sapida
fruits desiccated in silica gel
R. sapida has some desiccation tolerance but its
storage behaviour is non-orthodox
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Moisture determination in non-orthodox seed
Corynocarpus laevigatus
Fleshy fruit
Embryo axis 0.06
Endocarp
Cotyledon 99.94
(From Moore and Irwin, 1978)
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Moisture determination in non-orthodox seed
Corynocarpus laevigatus
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Moisture determination in non-orthodox seed
Dysoxylum spectabile
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Moisture determination in non-orthodox seed
Dysoxylum spectabile
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Moisture determination in non-orthodox seed
Dysoxylum spectabile arillate seed
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Moisture determination in non-orthodox seed
Dysoxylum spectabile
( Myoung Joo Park, unpublished data)
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Moisture determination in non-orthodox seed
Dysoxylum spectabile
( Myoung Joo Park, unpublished data)
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Moisture determination in non-orthodox seed
Dysoxylum spectabile
( Myoung Joo Park, unpublished data)
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Questions

• How does this impact on the current ISTA methods
  for moisture determination in non-orthodox tree
  and shrub species?

• Poulsen et al., 1998 suggested that only clean,
  firm and apparently alive seeds should be
  selected for moisture determination in
  non-orthodox seed. Agree or disagree?

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Acknowledgments

• Members of the ISTA Moisture Committee in
  particular Deon Erdey (South Africa)
• Heather Outred, Kay Kitchen, Robert Southward,
  David Fountain, Myoung Joo Park, Bruce MacKay,
  Warren Williams
• Chris Wood
• Kapiti Coast District Council
• Massey University and Royal Botanic Gardens,
  Kew.