Tissue proliferation condition in micropropagated ericaceous plants

Abstract

Tissue proliferation (TP) is an abnormal tumor-like growth produced at or near the crown of the plant, but may also be found on aerial plant parts of some genotypes. Basal tumors may or may not be accompanied by proliferation of compact shoots with short internodes and a whorled leaf arrangement. Genera exhibiting TP include Rhododendron, Kalmia and Pieris of the Ericaceae family. Development of TP symptoms in a plant is highly correlated to a history of micropropagation and also to genetic background of the genotype. Similarities of TP symptoms to crown gall caused by Agrobacteriumtumefaciens led many to initially believe TP to be a form of crown gall, but all evidence suggests that a pathogen is not involved in the TP disorder. Abnormal lignotuber formation is another possible cause for TP for which little supportive evidence could be developed. An epigenetic condition, possibly cytokinin habituation, is the possible cause of TP that is best supported by the majority of research evidence. It is likely that TP is induced in vitro by adventitious shoot formation, resulting from high cytokinin concentrations used to rapidly proliferate shoots. Some nursery production practices may result in increased TP symptoms development post-propagation. TP is well managed now due to greater awareness and adoption of sound micropropagation practices for ericaceous plants by tissue culture labs.