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ISHS Acta Horticulturae 901: XII International Symposium on Virus Diseases of Ornamental Plants

VIRUS ELIMINATION AND RETENTION OF FREE BRANCHING IN POINSETTIA

Authors:   E. Fl°istad, C. Spetz, D.-R. Blystad
Keywords:   Euphorbia pulcherrima, phytoplasma, Poinsettia mosaic virus, thermotherapy
Abstract:
A heat treatment scheme for the elimination of Poinsettia mosaic virus (PnMV) in poinsettia stock plants was applied to one set of stock plants for a period of nine months, and to a second set for twenty months. The process of PnMV elimination in shoot tips was monitored by repeated testing by ELISA. Rooted cuttings that were free from PnMV were evaluated for retention of phytoplasma by assessing their ability to form branches on the basal part of the stem before pinching. Out of 926 cuttings established from the first set of stock plants, 99 were free from PnMV. Among the PnMV-free cuttings, 29 were also free branching, demonstrating that phytoplasma was retained. The proportion of PnMV-free cuttings increased with time in heat treatment, from 0% after 4 months to 70% in the last propagation after seven months. In total, heat therapy was applied to 5 commercial varieties: four produced PnMV free cuttings in varying numbers, while one variety produced no PnMV-free cuttings at all. We have monitored the PnMV status in the resulting clean stock. Nuclear stock plants kept in a screened greenhouse, isolated from any potential infection source, have continued to test negative by ELISA. These results have been verified by PCR. However, plants derived from this nuclear stock and used in trials in commercial greenhouses have frequently become reinfected.
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