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Seasonal variations in rose mosaic disease severity and risks associated with using non-symptomatic plants from contaminated crops

Susannah Wright: North Florida Research and Education Center, University of Florida

<div>Rose Mosaic Disease (RMD), caused primarily by <em>Prunus necrotic ringspot virus </em>(PNRSV) and <em>Apple mosaic virus</em> (ApMV), has been an ongoing issue for rose growers in the U.S. Field trials were conducted in North Florida to determine the correlation between the initial RMD severity (%) compared to the final disease severity (AUDPC) in fall 2014, spring 2015, and fall 2017 seasons, and to understand the risk factors in using non-symptomatic roses from contaminated crops. The severity ratings were taken on 121 Pink Double Knockout roses in fall 2014 and in spring 2015; and on 43 infected rose varieties in fall 2017. There was a very strong positive correlation between initial disease severity and final AUDPC in fall 2014 (r = 0.953; Pearson’s correlation P = 0.01), and a positive correlation in spring 2015 (r = 0.560; P = 0.01). A significant number of the non-symptomatic plants became symptomatic during the period of the experiment; 33%, 90% and 34% in fall 2014, spring 2015, and fall 2017, respectively. The general trend was for disease severity to increase as the temperature increased, and to decrease as the temperature decreased. However there were a few exceptions to this general trend. These results indicated that it might not be safe for a nursery to invest in non-symptomatic roses if rose mosaic disease was confirmed in a small subset of the same crop.</div>