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United States Department of Agriculture

Agricultural Research Service


item Zimmerman, Richard

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/2/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Tissue proliferation (TP) is a disorder characterized by gall- like growths on the lower stems of rhododendron plants; the TP galls sometimes produce numerous adventitious shoots. TP is usually first observed on 2-3-year-old plants, but it can develop on younger ones. Although the TP growths resemble and have been confused with crown gall, current evidence indicates that it is not crown gall. Gall formation has not been induced following inoculation with numerous strains of Agrobacterium tumefaciens. Galls are found primarily on micropropagated plants, but have also been observed on cuttings never tissue cultured and on young seedlings. The disorder appears to be genotype related, with some cultivars frequently affected and others rarely if ever showing the problem. Although TP was originally observed on elepidote rhododendrons, it sometimes occurs on lepidotes and on Kalmia. High cytokinin levels in the proliferation medium may be implicated in the occurrence of TP in micropropagated plants and have resulted in cytokinin habituation in cultures of one cultivar. Plants produced from adventitious shoots, easily obtained with high cytokinin concentrations, may be more likely to develop TP. Some species of Rhododendron and other ericaceous plants naturally form lignotubers and these species may also be more susceptible to TP. Nursery practices, such as high fertilization levels and use of some growth regulators and herbicides appear to increase the incidence of TP, as do high temperatures in the root zone and water stress.

Last Modified: 06/27/2017
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