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Funded Project

Funding Program: IPM Enhancement Grants

Project Title: Exploring critical use of a Systemic Acquired Resistance inducer against Rose Rosette Disease

Project Directors (PDs): Mathews Paret [1] Gary Knox [2] Binoy Babu [3]

Lead State: FL Lead Organization: University of Florida

Undesignated Funding: $29,960

Start Date: Mar-01-2016 End Date: Feb-28-2017

No-Cost Extension Date: May-31-2017

Pests Involved: Rose Rosette Virus

Site/Commodity: Roses

Area of Emphasis: IPM

Summary: Roses are one of the most popular flowering shrubs in the U.S with a wholesale value of $194 million (USDA, 2010). Rose rosette disease caused by Rose rosette virus, an Emaravirus has become the most devastating disease on roses in the recent years, causing huge economic losses to nurseries, landscapers and gardeners throughout the U.S (Laney et al., 2011). The virus is vectored by an eriophyid mite species Phyllocoptes fructiphilus and budding or grafting can also transmit the disease. The symptoms of rose rosette disease include abnormal lateral shoot growth, excessive thorniness, witches broom, leaf proliferation and distortion, mosaic, and red pigmentation of the leaves and the stems. The disease leads to the death of the infected plants in 1-2 years. The disease affects many rose species and cultivars and has been spreading through much of the wild and cultivated rose population of the Midwestern, Southern, and Eastern U.S. Of particular relevance is the high susceptibility of traditional rose varieties and Knock Out series of roses in the U.S. Thus, rose rosette disease is a major threat for rose producers and the landscape industry in the U.S. The impact of rose rosette disease in rose growers own words can be found in the following link from AmericanHort; Rose Rosette from the Industry eyes; and the southern nursery IPM (SNIPM) working group has listed rose rosette disease as the second topmost priority among plant diseases in the region in 2014; http://www.sripmc.org/policy/priorities/SNIPM_Priorities.pdf. A significant limitation in managing rose rosette disease is the lack of any chemical control options. Our proposed seed project aims to study a chemical control option utilizing a Systemic Acquired Resistance (SAR) inducer, which has shown encouraging results in our preliminary trials in Florida. ASM (Actigard"; labeled on vegetables and fruit trees, but not on roses; Syngenta, 2015) is a SAR inducer and activates the plant defense system by increasing the transcription of stress related genes. ASM by itself or integrated with other methods has been shown to protect plants from Tomato spotted wilt virus in Tomato and Tobacco (Mandal et al; 2008; Momol et al., 2004), and Iris yellow spot virus in Tobacco (Tripathi and Pappu, 2015). A preliminary study by our team showed that foliar applications of ASM at e50 mg/L, on Knock Out roses followed by budding plants with buds from Rose rosette virus-infected plants, did not produce any symptoms of the disease, as compared to drench application of ASM or non-treated controls which showed high disease severity as indicated by the Area Under Disease Progress Curve (Fig. 1; Horsfall and Barrett, 1945). Real-time RT-qPCR testing of the plants treated with foliar application of ASM further confirmed the absence of Rose rosette virus till date (>6 months from the start of the experiment; data not shown). This finding strongly indicates to the potential of ASM in protecting roses from Rose rosette virus, which may be due to the prevention of the virus movement, or replication from infected buds to healthy plants leading to no symptoms or reduced expression and thus needs to be further studied and validated. Objectives: The objectives of the study are 1.To evaluate the ability of Acibenzolar S-Methyl (ASM), a Systemic Acquired Resistance inducer (SAR), in protecting roses from rose rosette disease 2.To assess the ability of ASM integrated with removal of infected branches in reducing disease severity. 3.To evaluate the effect of ASM on roses through growers participatory testing and training growers on early field identification of the disease.

Final Report:

Outputs 1. Three trials were conducted to evaluate the effectiveness of ASM in reducing disease severity of rose rosette disease if applied preventatively. Real time PCR was used to test the present or absence of Rose Rosette virus in these plants. 2. Two trials were conducted to evaluate a combination of removal of infected branches, pruning of the entire plant and ASM foliar applications in reducing rose rosette disease severity. 3. Two growers participatory trials were conducted to evaluate the impact of ASM applications on flowering and plant quality. 4. A training program was conducted for rose producers, landscapers and extension agents on improving knowledge on rose rosette disease.

Outcomes 1. Plants treated with ASM by foliar applications at 50 mg/L significantly reduced rose rosette disease severity compared to the non-treated control (P=0.05, SNK), in two trials. The plants did not exhibit any phytotoxicity at 50 mg/L. Real-time PCR on non-symptomatic plants before and after pruning confirmed the absence of the Rose rosette virus in these plants, while all non-sympomatic plants tested positive. One trial had poor disease and hence was not taken into analysis. This indicated and further confirms that preventative application of ASM could be useful in reducing disease severity of rose rosette disease. This needs to be now studied under field conditions in the presence of the vector eriophyid mite Phyllocoptes fructiphilus. 2. The two trials which tested integration in branch removal, pruning and ASM application showed no effect in reducing rose rosette disease severity. This confirms that ASM do not have curative properties against rose rosette disease. 3. The two grower participatory trials confirmed that ASM at 0.5 oz/A had no significant negative impact on Pink Double Knock Out and Pink Drift with respect to flowering and plant quality. However higher rates oy 0.75 - 1.0 oz/A have some marginal effects on flowering and plant vigor in Pink Double Knockout. 4. Among the attendees of the rose rosette disease training program 23 completed a review which was rated on a 0-5 scale, 0 indicated to no knowledge, 2 - some knowledge, 3 - medium knowledge, 4 - high knowledge and 5 - very high knowledge. This showed that their average knowledge on rose rose disease, the virus and the vector significantly increased from 2.39 at the beginning of the program to 3.95 at the end of the training (P=0.01)

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