Home Publications Evaluating Seedling Quality: Principles, Procedures, and Predictive Abilities of Major Tests 06: Seedlings morphological evaluation-- What you can tell by looking

06: Seedlings morphological evaluation-- What you can tell by looking

Grading for height and root collar diameter is practiced by many nurseries as a basis for separating out stock of poor quality. Experiments relating seedling size to field performance are rather contradictory. In general, when seedling physiological status is equal, larger seedlings grow better but often do not survive as well as smaller stock. Diameter is the best single predictor of field survival and growth. Seedling weights often correlate with field survival through their high correlation with stem diameter. Bud height can be used as a measure of potential field growth. Color indicates the nitrogen fertility regime used in the nursery but is only related to outplanting response under certain conditions. The presence of succulent shoots, foliage length, foliage density, multiple tops, and stem sweep is often included in grading standards, but little is known about their subsequent effect on performance. The desired morphology of the root is less defined than the shoot. Research supports the generalization that seedlings with more roots outperform those with less roots. No measure exists that determines how much root is sufficient. Shoot/root ratio has been used for this purpose, and it may be of substantial value when corrected for seedling size in predicting field survival. Other root morphological attributes such as stiff laterals, swept roots, root configuration, root damage, and the presence of mycorrhizae, may affect growth and survival, but little conclusive evidence exists. Since one parameter seldom explains all the variability seen in the field, morphological indices have been developed that incorporate a number of measurements, such as height, diameter, and dry weights. Some of these show promise in predicting field performance. Although physiological condition can override morphology, the size and shape of the plant does, in many instances, reflect its potential for field survival and growth. Nursery managers can be reassured that grading is beneficial.


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Author(s): Barbara E. Thompson

Publication: Evaluating Seedling Quality: Principles, Procedures, and Predictive Abilities of Major Tests

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