Rose Mosaic Disease: seasonal variation in disease severity and risk factors in using non-symptomatic plants Susannah Wright, Binoy Babu, Laura Ritchie, Barron Riddle, Gary Knox, Mathews Paret North Florida Research and Education Center, Quincy, FL •Described 1928: “An infectious chlorosis of roses”, R. P. White •In the U.S., primarily caused by Prunus Necrotic Ringspot Virus (PNRSV) and Apple Mosaic Virus (ApMV) •Hosts: •PNRSV (almond, apricot, cherry, hop, plum, rose, …) •ApMV (almond, apple, apricot, blackberry, cherry, hop, pear, rose, strawberry, …) • Florida wholesale rose industry over $30 million
Transcript
Rose Mosaic Disease:seasonal variation in disease severity and risk
factors in using non-symptomatic plants
Susannah Wright, Binoy Babu, Laura Ritchie, Barron Riddle, Gary Knox, Mathews Paret
North Florida Research and Education Center, Quincy, FL
•Described 1928: “An infectious chlorosis of roses”, R. P. White•In the U.S., primarily caused by Prunus Necrotic Ringspot Virus (PNRSV)
• Florida wholesale rose industry over $30 million
Rose Mosaic SymptomsSymptoms may include the following:
• Blossom disfigurement• Reduced blossom production • Reduced plant vigor• Chlorotic patterns on foliage• Foliage distortion• Often show symptoms in spring• Sometimes, no visible symptoms
Transmission• No evidence of mechanical transmission • No evidence of seed or pollen transmission • Possible natural root grafting
Presenter
Presentation Notes
Shown here are a few symptoms that we see out in the field. Among those not shown here are reduced plant vigor, reduced flower quantity and quality. There has been a lot of research done by other groups showing a myriad of consequences of this disease. �Symptom expression is not necessarily an indicator of virus severity. �Symptom expression can depend on a variety of things, such as the strain of virus present, rose cultivar, environmental conditions – we are currently looking at different rose cultivars to see how severely different cultivar expresses the virus. Symptoms include: Mosaic patterns on leaves Ringspots Chlorotic patches Line patterns Vein netting Foliage distortion A combination of any of the above In the 1982, a paper was published showing that plants with Rose Mosaic, even if they do not show symptoms of the mosaic, they tend to be less vigorous than plants without the virus (Thomas, 1982) Several different studies have indicated that Rose Mosaic can cause stunting, reduced flower quality and quantity – in some cases, plants will not show these issues In other host plants, mechanical, seed, pollen, and grafting transmission have been shown to transmit these viruses. In roses, as far as has been determined, none of these modes apply, except possibly grafting. The relevance of this is that: Growers need to understand how it spreads, how to detect it, and how to avoid having it – if you are a nursery, and you are shipping roses cross-country, and they arrive with symptoms – even a single leaf – your entire shipment can be rejected. �
Objectives
• Determine the correlation between initial rose mosaic disease severity compared to Area Under Disease Progress Curve (AUDPC) during spring, summer, and fall seasons in North Florida
• Understanding risk factors in using non-symptomatic plants
Why is this study relevant? Seasonal variations in disease severity has been recorded
before, but the risk factors in using non-symptomatic plants from lots with symptomatic plants is not well understood.
Critical information for whole-sale nurseries (and retailers) because their delivery could be rejected if even one plant shows up with symptoms upon arrival.
Relevant for landscapers as removal of infected plants and replanting with healthy ones increases expenses.
Presenter
Presentation Notes
We use the AUDPC because symptom expression is pretty variable – it depends on environmental factors – and this helps us to kind of normalize the data.
Plants confirmed for the presence of PNRSV, ApMV by PCR
Presenter
Presentation Notes
This graph displays the data from each year. X axis is the initial disease severity rating, the Y axis is the number of plants at that initial rating value. The first, blue bar, is Fall 2014 plants. Orange represents Spring 2015 plants. Gray represents Summer and Fall of 2017 (because the ratings ran from June 19 – October 10; which is basically from the start of Summer to when foliage was dropping off, and we were no longer able to rate). We decided to throw in several different varieties, albeit at a smaller varietal sample size, to see if maybe any trend might hold true for other varieties. We have 5 replicates of each variety, because we were unable to do a larger sampling for these varieties – it’s hard to take 250+ roses from a nursery… so, we took a small subset, to see if that could indicate anything to us.
5%
46%49%
Summer-Fall 2017 (n=77)
51%
16%
33%
Fall 2014 (n=57)
10%
90%
Spring 2015 (n=10)
INITIALLY NON-SYMPTOMATIC ROSES
Gray - Became symptomatic, Blue - Non-symptomatic, Orange - Became symptomatic but reverted to non-symptomatic
Presenter
Presentation Notes
These pie charts represent the first three bars from the previous slide. 2014, 2015, and 2017 initially non-symptomatic plants. Here, we are looking at those initially low plants, and a description of their behavior over the period of the trial. Blue represents non-symptomatic. Grey represents symptomatic, and orange represents ones that changed then reverted back to the original rating. Please note that, in the spring, most of them became symptomatic, and none of them reverted back.��
Fall 2014Spearman’s correlation coefficient, ρ = 0.929,
significant at 0.01 level
Spring 2015Spearman’s correlation coefficient, ρ = 0.527,
significant at 0.01 level
Fall 2014 and Spring 2015 AUDPC and Initial Disease Severity Correlation
Presenter
Presentation Notes
These are two graphs representing the initial % disease severity rating (x-axis) plotted against the final AUDPC. A Spearman’s correlation was done on both data sets, and it came out, as you see, as related, and is statistically significant at the 0.01 level, indicating that this correlation is real, and not just by chance. What this graph means is that, even though there are weekly variations in the disease severity, over time, it will all follow a general trend.
Conclusions• A high percentage (33-90%) of the non-symptomatic roses became
symptomatic at the end of all trials. • A smaller percentage (16-31%) of symptomatic roses became non-
symptomatic in fall trials. • Plants also reverted from symptomatic to non-symptomatic and back and
vice-versa• There was a strong positive correlation between initial rose mosaic disease
severity and disease progression over time in all trials (P=0.01)• Wholesale nurseries, retail nurseries/stores, landscapers, and general public
should absolutely avoid purchasing plants with any rose mosaic symptoms or roses from lots with any symptoms.Look at all plants in the lot and not just the plant/s that you want to buy!
• Additional information and data available on poster
AcknowledgementsFlorida Nursery Growers and Landscape Association Grant funding 2014-2015Dr. Binoy Babu (Former Post-doctoral Fellow) Nurseries (Anonymous) supporting our research efforts Dr. Fanny Iriarte, Plant Disease DiagnosticianDr. Melanie Kalishuk (Post-doctoral Fellow) Shomaila Iqbal and Kamil Duman (Former Visiting Scientists)Jim Aldrich, Laura Ritchie, and Barron Riddle (Biological Scientists)
