Imara ® XDR
The Latest in Disease Resistance Breeding and the Disease Management Toolbox Dr. Alicain Carlson and Dr. Jamie Gibson Perceptions around disease resistance genetics in the floriculture industry have become a hot topic with reports of disease outbreaks in resistant genetics raising questions about the resilience of the breeding, evolution of disease, efficacy of chemistries, and questions of what to do about it. In this article, we cover the realities and expectations of disease-resistant genetics, the basics of responsible disease management practices, and the place for non-resistant genetics with an emphasis on two key diseases: 1) Impatiens Downy Mildew (IDM, Plasmopara destructor , formerly Plasmopara obducens ) and 2) aerial Phytophthora ( Phytophthora nicotianae ). These diseases have significant impacts on our industry and are constantly evolving, so we must remain diligent in prevention and control with the entire toolbox of options available to us. At Syngenta Flowers, we have always, and especially since the launch of our XDR (“Xtreme Disease Resistance”) brand in 2019, advocated for a well-rounded, integrated approach to disease resistance management that emphasizes responsibility and stewardship. Disease resistance gained through genetic advancements has had a profoundly positive effect on the industry. These milestone genetic achievements paired with tried-and-true horticultural logic and a toolbox approach to plant diseases, yield the best, longest-lasting, and perhaps most importantly, the most responsible results. A focus on disease resistance
The breeders, pathologists, and plant scientists at Syngenta Flowers have been hard at work for decades developing tools to combat diseases that attack flowering plants and landscapes. The fundamental understanding that there’s no “silver-bullet” solution allows for a more holistic approach to controlling the devastating effects of various pathogens. Preventive and curative ornamental plant chemistries have long been employed in the greenhouse and by landscape professionals to lessen the damage of diseases, but with the introduction of more resistant genetics we have another tool in the toolbox.
XDR stands for Xtreme Disease Resistance
Syngenta Flowers has been breeding highly resistant varieties in several classes of traditional bedding plants with the launch of our XDR branded Cora ® vinca (resistant to over 30 strains of aerial Phytophthora) and Imara ® Impatiens walleriana (highly resistant to IDM) in 2019. To meet our internal standards, all XDR products must: 1) exhibit best-in-class performance under disease pressure; 2) endure rigorous testing in both field and lab settings around the globe; and 3) obtain independent verification from third-party experts. Breeding technologies in vegetables and agronomic crops have supplied a standard terminology set and knowledge base for how disease resistance is defined in agriculture. The Syngenta Group has long been a foremost breeding expert in disease resistance in many classes of food crops and we bring that strength to our Flowers business. It’s important to remember the difference between resistant and immune (see table on “Important resistance terminology”). For example, IDM infection on resistant genetics of I. walleriana may show sporulation of the pathogen with some minor leaf abscission, but you won’t see total defoliation. This means that the disease must still be prevented using the proper environmental and chemical controls. In 2019, a working group of horticulture and plant pathology leaders and academic specialists was created to ensure that everyone was aligned with parameters for claiming the various levels of disease resistance and consistent terminology was ultimately adopted for the floriculture industry.
Important Resistance Terminology
Immunity: When a plant isn’t subject to attack or infection by a specified pest High Resistance: Plant varieties that highly restrict the growth and/or development of the specified pest and/or the damage it causes under normal pest pressure when compared to susceptible varieties. These plant varieties may, however, exhibit some symptoms or damage under heavy pest pressure. Varieties claiming the same level of resistance against a specific pest may exhibit a different resistance response due to a different genetic makeup of a variety. Intermediate Resistance: Plant varieties that restrict the growth and/or development of the specified pest and/or the damage it causes but may exhibit a greater range of symptoms or damage compared to high resistant varieties.
Source: International Seeds Federation: Definition of the Terms Describing the Reaction of Plants to Pests for the Vegetable Seed Industry (Adopted by the ISF Vegetable and Ornamental Crops Section in May 2017)
Imara ® XDR Mix
Cora ® XDR Apricot
Cora ® XDR Vinca Series in Gilroy, CA Wk 33, 2021
Effective chemical tools for enhanced disease resistance management In order for resistant genetics to thrive the proper use of chemistries is imperative. Fungicide rotations prescribed to prevent IDM in Impatiens walleriana may also help protect from other serious fungal pathogens that they’re susceptible to, including Pythium, Phytophthora, Rhizoctonia, Thielaviopsis, Myrothecium, Alternaria and Botrytis . For these reasons, base level preventive fungicide applications are recommended during propagation and finished production for general sanitary and stewardship reasons. It’s important to understand the pathogens that a crop was specifically bred to resist against and that “disease resistance” does not imply a resistance to all diseases it could get infected by. By principal, plant pathologists emphasize that in order to properly fight a disease you must diagnose the specific pathogen first. This practice not only allows you to choose the proper chemical treatment but also the most appropriate genetics to produce.
Syngenta Flowers has a vast online library of information available for these treatment options and many technical experts that can provide suggestions and rotation schedules. Rotation of active ingredients is the key to crop protection and demonstrates best disease resistance management practices. Nancy Rechcigl, Technical Services Representative for Syngenta’s Turf and Ornamental Controls business, suggests a systemic sandwich for effective management of the disease—chemistries applied during plug production/at transplant and before shipping to retail centers. For an effective and specialist prescribed agronomic program with multiple rotation active ingredients please visit the GreenCast Online Website.
Measuring Genetic Performance In order to see the true genetic performance, all breeding and selection work for Imara ® XDR and Cora ® XDR was done without preventive chemistries. Syngenta Flowers stands strongly behind our message of resistance, and the collective expertise suggests continuing to safeguard these important classes by taking a more steady and responsible approach to maintaining genetic disease resistance through coupling with preventive chemistries.
This program contains a fairly new FRAC group 49 fungicide tool called Segovis ® . This fungicide offers a unique mode of action to diversify rotation programs and protect impatiens for up to 12 weeks when applied as a drench as the final treatment prior to shipping. Segovis ® has been encouraged by Extension Plant Pathology Specialists Dr. Mary Hausbeck, Michigan State University and Dr. Margery Daughtrey, Cornell University.
Impatiens Downy Mildew Trials Vero Beach, Florida
Existing Commercial Variety
Transplanted and inoculated with Downy Mildew on March 1, 2018. Photographed on April 30, 2018. Imara ® XDR Red
A place for non-resistant genetics Non-resistant genetics have a place in our industry. They offer a wide range of colors, can be grown where the particular disease pressure is not as severe, and are an economical option for growers. Untreated resistant genetics can still be a host for pathogens, so regardless of the potential of having resistant and non-resistant genetics being produced in the same facility, preventive chemistries will always be a necessity . Syngenta Flowers continues to emphasize a safeguard approach by using preventive fungicides, especially in propagation and prior to shipping. From packs for garden borders and landscape beds, to hanging baskets for home gardeners, the proper use of fungicides from propagation to finish is essential to each consumer’s success. With appropriate rotation tools non-resistant genetics can still perform in the landscape for many weeks providing consumer satisfaction.
Landscaper Tech Tip: Assurance for delivering season long performance
Recognizing the achievements, but always striving for improvements The Syngenta Flowers Team is proud of these achievements in advanced disease-resistant breeding and has gained attention in trials around the globe. Imara ® XDR Impatiens first launched in the European market and sold out immediately at retail outlets around the United Kingdom. Consumers were “taking back the shade” and were delighted to have a garden favorite on the retail shelves again. Imara ® XDR Impatiens won the 2019 TASPO Award of the Year for Best Breeding Product and it was awarded for Best Ornamental Plant Introduction—Bedding by Horticulture Week Business Award in London in June 2019. Cora ® XDR is currently the industry-leading disease-resistant vinca around the globe. As flower breeders, we must constantly work on new varieties to keep up with the evolution of diseases that occur naturally. Coupling resistant genetics with other modes of action to control disease is Syngenta’s “responsible mindset” message, reminding growers and landscapers that we must rely on more than one tool when managing diseases. The technical plant scientists and pathologists at Syngenta Flowers have been supporting the bedding plant and landscaping industry’s battle with these problems for decades, providing chemical rotation schedules, common-sense culture tips and grower-specific recommendations to lessen exposure and provide preventive and curative control to these diseases. We know from our long breeding history in vinca and impatiens that we must keep ahead of the disease evolution and remain vigilant in our selections, screenings, and validations. To read more about the historical journey of our disease resistance breeding in these classes please see this article. With recent reports of disease outbreaks, it reminds us that we must all stay vigilant in the disease management process. Growers, landscapers, Extension personnel, and other industry professionals should report new outbreaks of disease when these new innovations and protective measures have been put in place. This high degree of scouting will only strengthen our industry. It’s clear that there’s no one-tool approach to complex disease problems, so please brush off that toolbox and get to work. Landscapers, starting with properly treated plant materials sets you up for success, but there are further actions you can take to improve disease resistance management. Keep in mind that oospores of IDM can overwinter in many parts of North America; a preventive fungicide treatment to ground beds in late summer may help further protect impatiens until first frost. This application may not only prevent an outbreak of IDM at this time, but also preserve planting options for the following spring. Certified professional landscapers should make soil applications to ground beds after transplanting in the spring, particularly when cool, moist conditions prevail or when disease pressure is known to be high in the region. Environmental conditions in the fall are also favorable for this disease. Avoid repeated applications of the same active ingredient to reduce the risk that the disease will become resistant. Subdue ® GR (granule) fungicide or phosphite-containing products are popular garden protectants.
All photos are either the property of Syngenta or are used with permission. © 2023 Syngenta. Some or all of the varieties may be protected under one or more of the following: Plant Variety Protection, United States Plant Patents and/or Utility Patents and may not be propagated or reproduced without authorization. Important: Always read and follow label instructions. Some products may not be registered for sale or use in all states or counties and/or may have state- specific use requirements. Please check with your local extension service to ensure registration and proper use. Trademarks are the property of their respective owners.
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