Agriculture Reference
In-Depth Information
The 50% rule
In general, seedlings are classiied as normal if half or more than half of their total cotyledonary tissue
is functional but abnormal if more than half of their cotyledonary tissue is nonfunctional (e.g., missing,
necrotic, discolored, or decayed). However, some exceptions to this rule exist and analysts are advised to
refer to speciic AOSA or ISTA rules. For example, in some large-seeded epigeal Fabaceae species, the
cotyledons may be missing, provided the seedling is otherwise normal and vigorous (AOSA, 2010).
Lesions in dicotyledonous Species
The root-shoot axis of dicots is made up of a cylindrical stele that includes conducting tissue, surrounded
by cortex and epidermis. Deep open cracks that extend to the stele are considered abnormalities since they
hinder the movement of water and nutrients to growing parts and increase a seedling's susceptibility to
micro-organism attack. Whenever a lesion or crack is observed along the root-shoot axis, the analyst must
determine whether the conducting tissue of the stele is affected. Unless the crack or lesion is obviously
very deep, an examination under the microscope might be necessary. Because of the dificulty of direct
observations and anatomical variations among species, AOSA rules recommend that analysts familiarize
themselves with hypocotyl and epicotyl cross sections of regularly tested species under the microscope.
SEEdLInG EVALuATIon of dIffErEnT rEPrESEnTATIVE fAMILIES
The following pages show drawings of normal and abnormal seedlings of different representative plant
families.
While these drawings are not intended to show oficial representations of any seed testing
organization
, they will be helpful to the beginning or even experienced analyst in illustrating the general
principles of seedling evaluation and the kinds of structural abnormalities often encountered in the labora-
tory. Consequently, they should be studied carefully and can be used to learn the principles of evaluating
seedlings for germination. (All drawings by Sabry Elias.)
