Agriculture Reference
In-Depth Information
6. A well developed, straight coleoptile in Poaceae, with a green leaf growing inside up to the tip and
eventually emerging through it.
Seedlings with the following slight defects in their essential structures are classiied as normal, accord-
ing to ISTA, provided they show an otherwise normal and balanced development in comparison with intact
seedlings from the same test.
1. Root system:
- the primary root with limited damage, such as discolored or necrotic spots, healed cracks and
splits or cracks and splits of limited depth;
- the primary root defective, if there is a suficient number of normal secondary roots. This
applies only to certain genera such as
Zea
. For other genera such as
Allium, Lycopersicon
, a
normal primary root is essential.
2. Seedling stem:
- the hypocotyl or epicotyl with limited damage, such as discolored or necrotic spots, healed
breaks, cracks, and splits;
- cracks and splits of limited depth; loose twists.
3. Cotyledons:
- the cotyledons with limited damage, such as discolored or necrotic spots; deformed or dam-
aged cotyledons, if half or more of the total tissue is left functioning normally (the 50% rule,
described later in this chapter);
- only one normal cotyledon in dicots, if there is no evidence of damage or decay to the shoot
apex or surrounding tissues;
- three cotyledons instead of two, providing they comply with the 50% rule.
4. Primary leaves:
- the primary leaves with limited damage, such as discolored or necrotic spots; deformed or
damaged primary leaves, if half or more of the total tissue remains and is functioning normally;
- only one normal primary leaf (e.g.,
Phaseolus
) if there is no evidence of damage or decay to
the terminal bud;
- three primary leaves instead of two (e.g.,
Phaseolus
), providing they comply with the 50% rule.
5. Shoot apex:
- the coleoptile with limited damage, such as discolored or necrotic spots; the coleoptile with a
split from the tip downward, extending not more than one-third of the length;
- the coleoptile loosely twisted forming a loop because it was trapped under glumes or fruit coat;
- the coleoptile with a green leaf not extending to the tip, but reaching at least half-way up the
coleoptile.
Pathogen/Saprophyte Infestations
The infestation of seedlings with fungi or bacteria may cause dificulty with their classiication as normal
or abnormal. The AOSA and ISTA rules specify that seedlings infected with fungi or bacteria be considered
normal if they are otherwise normal. This means that contaminated or infected seeds damaged because of
proximity to a diseased or abnormal seedling are classiied as normal if all essential structures are present.
When contamination and seed decay are suspected or known (usually after the irst count), germination
counts should be made at approximately two day intervals until the inal count. During these counts, dead
and moldy seeds should be removed from the substratum to minimize further contamination of otherwise
healthy seeds and seedlings and their number recorded. In addition, when disease symptoms develop and
are recognized, their presence should be reported. However, it should not be assumed that irm, ungermi-
nated seeds contaminated with fungi or bacteria are dead.
