Agriculture Reference
In-Depth Information
examination of the cotyledon and terminal bud. If seed coats cannot be removed without seedling damage
(due to necrotic cotyledons or decay), such seedlings should be considered abnormal.
Well developed normal seedlings should be removed at irst count to avoid entanglement of their roots
or collapse of other seedling structures with slowly developing seedlings. However, doubtful or damaged
and deformed or unbalanced seedlings should be left until the inal count to reduce incorrect evaluation.
Seedlings that have not reached an appropriate evaluation stage by the end of the prescribed period
may be assessed according to the analyst's best knowledge and experience. The appearance of other seed-
lings in the germination test may be used as a guideline. However, if a comparatively large number of unde-
veloped and doubtful seedlings remain, the test should be prolonged, and appropriate investigations made
to determine whether seedlings are normal (see AOSA or ISTA seedling evaluation criteria for application
of germination test extensions speciic to genera).
diseased and decayed Seedlings
When decay is present in a germination test, examination should be made at approximately two-day inter-
vals between the irst and inal counts. Obviously dead and moldy seeds should be recorded and removed
after each examination. Samples should be retested if infestation is extensive enough to make evaluation
dificult, or if improper test conditions may have contributed to infestation development. Practices to mini-
mize fungal and bacterial spread include: wider spacing of seeds on substrata, rapid removal of decayed
seedlings, proper substratum moisture content and adequate aeration. Retesting in sand or soil usually
reduces secondary infection levels.
Multiple Seed units and Coated Seeds
Seed units containing more than one true seed (e.g.,
Beta vulgaris, Tetragonia tetragoniodes
) or multiple
lorets of certain grasses (e.g.,
Dactylis glomerata
) are tested as single seeds and are classed as normal if at
least one seedling develops and continues to grow under favorable conditions. When a seed unit (a single
cluster or multiple loret) produces two or more normal seedlings, it is counted as one normal seedling.
Coated seeds or seed units should be placed on germination substratum in the same condition in which
they were received. No rinsing, soaking, or other treatment should be given. Each coated seed is considered
a seed unit for counting purposes. If symptoms of phytotoxicity occur on seedlings from coated seeds
placed on artiicial germination substrata, a retest should be conducted in sand or soil. If coated seeds are
received with a request for a test on decoated seeds, then the germination report should include speciic
information about the decoating procedures.
Hard, Swollen, dormant, and dead Seeds
Hard seeds are seeds which remain hard at the end of the prescribed test period because they have not
absorbed water due to an impermeable seed coat. Percentages of hard seeds in a germination test will vary
depending on seed age, kind, variety, and moisture content. Hardseededness in some freshly harvested
legumes such as red clover, lespedeza, and ield peas may decrease rapidly within the irst weeks or months
of dry storage. Conversely, seeds of okra or vetch and other legumes may increase in hard seed content
during dry storage. Hardseededness in beans increases as the seeds become desiccated. Relative humidity
during storage also may cause moisture changes within seeds that inluences the level of hardseededness.
It is important to realize that hardseededness is transient and can quickly decrease with time. Percentage of
hard seeds should be reported in addition to the percentage germination.
Swollen seeds are those that have imbibed but have not germinated (swollen seeds may or may not
appear larger than seeds that have not imbibed). They may be observed in germination tests of Fabaceae,
Convolvulaceae, Geraniaceae, and Malvaceae. Swollen seeds may or may not be viable. Sometimes, a
