Agriculture Reference
In-Depth Information
Uniform germination results cannot be achieved unless precise laboratory procedures are followed
(see Chapter 5 on germination testing). These procedures include the use of an unbiased working sample
subdivided from a representative, properly drawn larger sample. They also include the use of a standard
number of seeds for testing, adequate spacing of the seeds on the germination medium, and correct regula-
tion of substratum moisture. The equipment and substratum must provide and maintain, throughout the test
period, the conditions of moisture, temperature, aeration, and light that are needed to induce various kinds
of seeds to germinate.
Evaluation of germinated seeds is just as important as enabling them to germinate. The AOSA deines
normal seedlings as: “seedlings possessing the essential structures that are indicative of their ability
to produce normal plants under favorable conditions.” Note: the ISTA deinition of a normal seedling
incorporates “... development into a normal plant when grown in good quality soil under favorable condi-
tions of moisture, temperature and light. This capacity for continued development depends on the sound-
ness and correct functioning of the developing structures during germination.”
Experience has shown that intact seedlings (those having all essential parts) that are healthy, complete,
and well balanced, as well as seedlings with certain slight defects, are capable of producing a normal plant
under favorable conditions. Seedlings that have become diseased or decayed as a result of secondary infec-
tion from adjacent seedlings must also be classiied as normal.
An intact seedling, as described by ISTA, shows a speciic combination of the following essential
structures depending on the kind of seed being tested. Refer to section 2 of this chapter for descriptions and
illustrations of the seedling parts.
1. A well developed root system:
- a long and slender primary root, usually covered with numerous root hairs and ending in a ine
tip (e.g., Allium, Carthamus );
- secondary roots in addition to the primary root, produced within the oficial test period (e.g.,
Zea , Cucurbita );
- several seminal roots instead of one primary root in certain genera (e.g., Triticum , Cyclamen ).
2. A well developed seedling stem:
- a straight more or less slender and elongated hypocotyl in species with epigeal germination
(e.g., Cucumis, Pinus );
- a short (in certain cases), hardly distinguishable hypocotyl, but a well developed epicotyl (e.g.,
Asparagus , Pisum ) in species with hypogeal germination;
- an elongated hypocotyl and an elongated epicotyl in some genera with epigeal germination
(e.g., Glycine , Phaseolus );
- a more or less elongated mesocotyl in certain genera of the grass family (e.g., Sorghum ).
3. A speciic number of cotyledons:
- one cotyledon in monocots and rarely in dicots (e.g., Cyclamen ); it may be green and leaf-like
(e.g., Allium ) or modiied and remaining wholly or partly within the seed (e.g., Asparagus ,
Poaceae);
- two cotyledons in dicots; they are green and leaf-like expanded, the size and form varying
among species with epigeal germination (e.g., Brassica, Capsicum ), or hemispherical and
leshy and remaining within the seed coat in the soil in species with hypogeal germination
(e.g., Pisum, Vicia );
- a varying number of cotyledons (2 to 18) in conifers; they are usually green, long, and narrow.
4. Green, expanding primary leaves:
- one primary leaf sometimes preceded by a few scale leaves in seedlings with alternating leaves
(e.g., Cicer , Pisum );
- two primary leaves in seedlings with opposite leaves (e.g., Glycine , Phaseolus ).
5. A shoot apex or terminal bud, the development of which varies among species ( Phaseolus, Vigna ).
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