Vegetative propagation material is used in all areas of horticulture, such as bulbs (tulips and onions), tubers (dahlias and potatoes), runners (strawberries), cuttings (chrysanthemums and many trees and shrubs) and graft scions in trees. The increase of nematodes, viruses, fungi and bacteria by vegetative propagation is a particular problem, since the organisms are inside the plant tissues, and since the plant tissues are sensitive to any drastic control measures.
Inspection of introduced material may greatly reduce the risk of this problem. Soft, puffy narcissus bulbs, chrysanthemum cuttings with an internal rot, whitefly or red spider mite on stock plants, virus on nursery stock, are all symptoms that would suggest either careful sorting, or rejection of the stocks.
Accurate and rapid methods of virus testing (using test plants, electron microscopy and staining by ELISA techniques) now enable growers to learn quickly the quality of their planting stocks. Fungal levels in cuttings (such as Fusarium wilt of carnations) can be routinely checked by placing plant segments in sterile nutrient culture.
The quality of vegetative material is monitored in the UK by the Plant Health Propagation Scheme. In particular, it supervises the provision of six quality levels of plant material (Foundation, Super Elite, Elite, A, Approved and Healthy grades) for the soft fruit, top fruit and bulb industries.
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