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Seeing disease in a new light

Researchers look to light as a possible tool against powdery and downy mildews.

September 19, 2018  By Greta Chiu

Patel examines powdery mildew on summer squash prior to dosing the plant in a UV-C chamber. Photo credit: LRC, Rensselaer Polytechnic Institute

In a controlled environment, supplemental lights are often used to increase crop growth. But could they also be used for other purposes?

Research scientists Dr. Jaimin Patel and Leora Radetsky are exploring light as a way to mitigate disease. Working out of the Lighting Research Center (LRC) at the Rensselaer Polytechnic Institute, their research looks at using visible and ultraviolet (UV) light against powdery mildew and downy mildew – two of the most common diseases in the greenhouse.

With the rising demand for organic, locally grown produce and increasing attention on pesticides in consumer products, Patel and Radetsky’s findings could become a valuable tool in a grower’s toolbox.


We got in touch with Patel and Radetsky after their talk at Cultivate ’18 for a little Q&A.

Q: What prompted you to look into light as a possible tool against these mildews?

A: We started looking into using light to control powdery mildews based on our association with Dr. David Gadoury from Cornell University. David is a plant pathologist with extensive expertise at using UV for mitigating powdery mildew in numerous food crops. We have had recent success working with researchers from Cornell, University of Florida and Norway in applying UV treatments at night to reduce powdery mildew in field-grown strawberries.   

Dr. Jaimin Patel is a plant pathologist with expertise in downy mildew pathogens. He joined the LRC to investigate the efficacy of using light to reduce the disease severity for various food crops. Right now we are working on a spectral sensitivity function for basil downy mildew. Knowing how much light and which spectrum of light to use will allow cost-effective and disease-effective lighting solutions to be introduced.

Q: How does the technique work?

A: For basil downy mildew, these pathogens produce spores when it’s dark for an extended period of time, typically at night. If we give the right dose at night, we can supress spore production. Our research is investigating the most effective dose – how much, what spectrum, what time and for how long. We don’t know if light affects the host and/or the pathogen and if there is a circadian effect. We know that it does work and we are working to understand why.

For cucumber powdery mildew, we know that UV breaks down the pathogen’s DNA. It turns out that blue light repairs the DNA, which is why sunlight, which has both UV and blue spectral components, doesn’t prevent the pathogen from producing spores. We have found an effective solution by using UV at night without blue light.

We are interested in looking at other pathogens. Right now we are working on using light to control thrips with Dr. Margaret Skinner and Dr. Bruce Parker from the University of Vermont.

Q: Can it be made ‘broad spectrum’ to target more than one fungal disease?

A: The mechanisms within some pathogen groups may be the same, like pathogens that cause powdery mildews, but we don’t know if this is true for all pathogen groups. In practice, we have to make sure we give the right dose of light evenly over the entire crop. Time of application might also be important.  Pathogens have evolved with plants to “see” light during the day.  They may have their defenses down at night.  

Q: What fungal stage(s) are most responsive to light? How much light do you need and for how long?

A: Practically speaking, we have to give the right dose at the right treatment interval. For powdery mildews, UV is effective at reducing the disease during most stages. Downy mildew sporulation is inhibited, to various extents, by light, depending on the dose. The germination stage, in some downy mildews, is also inhibited by light, but we don’t know if the response is the same for all downy mildew-causing pathogens. We have been focusing on supressing spores so the pathogen can’t reproduce.

Q: Could the light harm the crop, and conversely, could it help the crop grow better if disease wasn’t an issue?

A: Of course – we don’t want to overdose or under dose the crop and pathogen. That’s why we talk about plant health – we also want to make sure that the lighting treatment doesn’t adversely affect the crop in any way, by making it look or taste bad for example. A recent paper of ours has been accepted for publication in the Canadian Journal of Plant Science. It shows that red light at night, which can be used to control basil downy mildew, can also increase yield in healthy basil plants.  

Q: Could it help save time and labour for greenhouses or indoor farms?

A: That’s a critical requirement in our research. We have a vision of a 24-hour lighting scheme for controlled environments, where lighting, controls and sensors are implemented to diagnose and treat pathogens and pests. Notably, light can be given after infection has occurred, so prescriptive chemical treatments could be reduced.

Q: Is it expensive to set up?

A: We don’t manufacture or sell lighting so we can only estimate the costs. If the grower has a lighting and control system that can already provide the right spectrum, the incremental costs should be minimal. We hope that a newly-installed lighting system for a controlled environment is cost-effective from a life cycle cost perspective. We are working with Dr. Natalia Peres from the University of Florida and David Gadoury to reduce the cost of the first successful prototype we developed for field-grown strawberries.

Q: How does this fit into an effective IPM strategy?

A: Pathogens can cause catastrophic losses, and we believe that all controlled environments could have pathogen problems, sooner or later. We see light as an adjunct to chemical treatments.

Like fungicides, we see an eventual path towards a light dosing label. Light is especially exciting for organic production because light is “organic”.

Q: What’s next for your research?

A: Through our IPH (Illumination for Plant Health) industry alliance, we are working on effective LED solutions for pathogens attacking greenhouse crops. We are also working on a field solution for powdery mildew in summer squash through New York Farm Viability Institute (NYFVI). We are working on using artificial intelligence (AI) to phenotype powdery mildew with Dr. David Gadoury and Dr. Lance Cadle-Davidson at Cornell.

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