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Laboratory
Evaluation of Lettuce Seedlings
Evaluation of Physiological
Necrosis
To
determine the value of the seed lot, the following diagrams of
cotyledon surface area were developed. Note that the three sets
of regulations used most frequently by a SCST member laboratory
treat the interpretation differently. Seedlings with cotyledons
showing some degree of physiological necrosis may otherwise be
perfectly healthy. Once any degree of physiological necrosis is
detected on the cotyledons of a lettuce seedling it can be
assumed that the storage life of that lot of seed is
dramatically reduced and the health of the seed lot also becomes
more vulnerable to less than perfect storage conditions.
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AOSA - Abnormal - 50%
or more necrotic
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ISTA - Abnormal - 50%
or more necrotic
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Canada - Abnormal -
Seedling showing any degree of physiological necrosis
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1. Cotyledons 65% necrotic | 2. Cotyledons 50%
necrotic | 3. Cotyledons 35% necrotic
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Diagram
from A.O.S.A. Seedling Evaluation Handbook Cont. No. 35.
1992. P.19, Fig 5.3.
(with permission) |
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