Testing for Physical Purity - Seed Testing - page 50

Seeds of fabaceae, brassicaceae and other Genera with Seed Coats removed
Seeds of Fabaceae, Brassicaceae, Cupressaceae, Pinaceae and Taxodiaceae must have at least some of the
seed coat intact in order to be considered pure seed. Only if the seed coat is entirely missing, is it considered
inert matter. Decorticated seeds cannot be identiied to species without the seed coat.
Insect-damaged Seeds
A deviation from the half-seed rule applies in the case of insect-damaged seed. If the damage is entirely
internal, the seed is considered pure seed regardless of the extent of the damage. If the opening in the seed
coat is so small as to make the extent of internal damage impossible to determine, the seed is considered to
be a pure seed (or other crop seed). Insect-damaged seeds of vetch and pea are considered pure seed regard-
less of the amount of damage unless they are broken into pieces one-half the original size or less.
Sclerotia and nematode Galls
Seed units of grasses containing nematode galls and fungus bodies (e.g., ergot, smut, etc.) that are entirely
enclosed within the seed unit are considered pure seed. If any part of the internal seed structure protrudes
from the tip of the seed, the unit is considered inert matter. Such galls and fungus bodies slip out of the
glumes easily when manipulated with the forceps. Nematode infected seeds have a “look” about them that
an experienced analyst learns to recognize. If nematodes are suspected, or a slight swelling is noticed, a
positive test can be made by crushing the seed-like structure, placing it in water for a few hours and then
examining it under a microscope. The nematodes (eelworms) become active and can be identiied easily by
their worm-like shape and motion.
WEEd SEEd
The AOSA rules list nine speciic kinds of seed-like structures which must be classiied as either weed seeds
or inert matter. Additional structures encountered in a purity test which do not seem to it into any of the
categories should be considered weed seed unless it can be shown that the embryo is missing. Observations
may be made by use of relected light over a diaphanoscope or by dissection. Crushing the seed should be
avoided since it destroys the seed material and opportunity for further observation.
Grass Florets With Empty, Underdeveloped or Broken Caryopses All lorets of grasses with caryop-
ses missing are classiied as inert matter. Free caryopses are classed as inert matter only if they contain
no endosperm or embryo. Special provisions have been made for classifying immature seed structures of
quackgrass (Elytrigia repens) which are frequently found in grass seed crops. If a caryopsis is less than one-
third the length of the attached palea (measuring from the base of the rachilla), it is classiied as inert matter;
otherwise it must be classiied as a weed seed. Caryopses with less than one-third development have no or
very little planting value. Free caryopses of quackgrass are considered inert matter if they are less than 2
mm in length.
Weed Seeds with Seed Coats Removed Seeds of weedy legumes and members of the Brassicaceae,
Cupressaceae, Pinaceae and Taxodiaceae with the seed coat entirely removed are classiied as weed seeds.
For more details refer to the AOSA and ISTA rules.
Immature Seed Units of Nongrass Species Lacking Embryo or Endosperm Development Immature
seed units devoid of both embryo or endosperm sometimes are found in such families as buckwheat
(Polygonaceae), morning glory (Convolvulaceae), nightshade (Solanaceae), puncturevine (Zygophyllaceae),