Tissue Proliferation on Rhododendron: A Current Perspective
Mark H. Brand
Tissue proliferation (TP) was first found in the mid-1980s and became a significant topic for propagators and growers by the early 1990s. The disorder is characterized by the development of callus-like tissue, often accompanied by adventitious buds and/or shoots, typically produced at the crown of rhododendron plants. TP has been observed on large-leaf and small-leaf rhododendrons, azaleas, and Kalmia latifolia. The superficial similarity in appearance of the gall-like growths or tumors of TP to crown gall caused considerable concern and problems for growers and nursery inspectors.
No evidence has been generated demonstrating that TP is caused by Agrobacterium tumefaciens or any other pathogenic organism. Today, it is generally believed that TP is not crown gall of rhododendron. The occurrence of TP mostly on micropropagated plants, or those with a history of tissue culture, has focused attention on the tissue culture process as a trigger for the development of TP in
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