The Incidence of Prunus Necrotic Ringspot Virus in Commercial Cut Flower Roses Grown Under Cover in Victoria.

Abstract

Prunus necrotic ringspot virus (PNRV) is one of a number of virus diseases that cause rose mosaic (3). The symptoms caused are typical of rose mosaic and include line patterning (5) although symptom expression depends on the strain of PNRV, the rose cultivar infected and the environmental conditions (2). In some cultivars flowering is delayed; autumnal leaf fall is earlier; more deformed flowers are produced, and although symptomless infection is common, infected plants are generally less vigorous (4). PNRV is only transmitted by grafting in roses (3). This paper reports a survey carried out in winter 1984 to determine the incidence of PNRV in cut flower roses grown commercially under cover in Victoria. Samples of young, soft leaf tissue were collected from 10 flower farms situated in outer metropolitan Melbourne. From five farms, 100 leaf samples were collected, 20 being taken at random from rootstock beds and 20 at random from each of four different cultivars. Four growers did not maintain rootstocks and from each of these farms 20 leaf samples were collected from each of 4 cultivars. At the remaining property only two cultivars were grown and 20 leaf samples were collected at random from each. The cultivars chosen for sampling on each property represented the most common varieties grown. Not all growers grew the same varieties. Growers who did not produce their own rootstocks purchased them as required from various sources, usually larger shrub rose producers. All samples were tested for PNRV using the enzyme-linked immunosorbent assay (ELISA) with antiserum, PV-AS-22 purchased from the American Type Culture Collection (1). Positive and negative controls comprising leaf samples extracted in the same way as the survey samples were included on each plate. A test was considered positive when the absorbance at 405 nm was more than twice that of the negative controls. Prunus necrotic ringspot virus was detected on all properties and in all cultivars tested (Table 1). In only one group of samples was no PNRV detected, those of the cultivar Ilona on the property of grower number seven. The incidence of infection was very variable and there was no