Don't Kill the Messenger

Lately among certain circles of daylily enthusiasts there has been much discussion about the new harpin proteins. Many of us have been trying to increase plant growth and at the same time, decrease our use of potentially harmful chemicals. Our lack of sufficient quantities of organic matter and soil quality has led us to increase our watering and the amount of fertilizer some add every year. Possibly related to this, might be an increase in insect and disease problems. Wouldn't it be nice if somebody could develop a single, environmentally harmless compound, which would increase plant growth and, at the same time, increase the insect and disease resistance of our daylilies?

Eden Bioscience claims to have just the sort of compound that many want. The compound is called Messengerâ and is a harpin protein, (actually harpinEa) isolated from the bacterium which causes fire blight on many fruit trees (Erwinia amylovora). The gene for this protein is then transferred to a harmless form of the Escherchia coli bacterium, which is raised in larger amounts and the harpin protein is isolated for our use. When a plant is exposed to this harpin protein, it is supposed to react as if it has been attacked. The discovery of harpin and its action was made by Zhongmin Wei¹, who was then a postdoctoral fellow and research associate working in Dr. Beer's lab. Wei is now the vice-president for research at Eden Bioscience.²

How it works

This Harpin protein has been reported to cause at least three separate responses:

1) Hypersensitivity – When invading pathogens come into direct contact with certain plant cells, those cells react and often die.

2) Systematic Acquired Resistance (SAR) – The response of many plants to harpin is to produce resistance to a large range of pathogens. Wei found that harpin treated tobacco plants were resistant to bacterial and viral pathogens of tobacco. Messenger® reportedly reduces damage caused by some insects through making plant material more difficult for insects to digest. Diseases listed on the label include bacterial spot and Phytophthora root rot of tomato and pepper; bacterial speck, root-knot nematode, and Fusarium wilt of tomato; and cucumber mosaic virus affecting cucurbits and eggplant.³

3) Increased growth – Harpin treated plants at both Cornell University and Eden grew larger and faster in the greenhouse than untreated plants. Eden researches in California, Mexico, Florida, and a few other southeastern states found similar increases in growth in cotton, citrus, peppers and tomatoes.⁴

Researchers at Cornell University determined that, as suspected, the harpin applied prior to infection tended to decrease the severity of infection. Thomas Zitter, professor of plant pathology, determined during a field trial on pepper plants that insect damage was decreased by the harpin protein. Field tests in the south confirmed earlier studies that indicated that growth of the plants was also stimulated. With disease resistance, insect resistance and increased growth all caused by the presence of harpin, the substance seemed to be a magic bullet to solve most of the problems of plant growers around the country.

A plant might evolve such a capability to allow it to be protected when under attack. The protein is thought to first effect the cell walls of the host (infected) plant. Infiltration of the compound into the intercellular spaces is the most effective way to produce the response. In the experiment by the developers of harpin, they say they found harpin responses "in many plants including tobacco, pepper, sunflower, tomato, cabbage, Arabidopsis, cucumber, geranium, watermelon and lettuce." Tissue infiltration seems to work well under laboratory conditions but might be more difficult under field situations. Ageratum, Celosia, Petunia and Vinca showed apparent improved growth with the treatment of Messenger® in the greenhouse.⁵

"Treating plants with the harpin protein signals the plant to turn on its natural defense systems," says Steven V. Beer, Cornell Univ. professor of plant pathology and one of the protein's discoverers in 1991. "The plant must be treated before the pathogen attacks, and it takes several days for the plant's system to mobilize its own defenses."⁶

Sales literature claims:⁷

1. "Harpins -- enhance a plant's own growth systems and natural defense mechanisms to ward off attacks by common diseases, insects and environmental stresses."

2. "Studies have found that plants treated with Harp-N-Tek (harpin) based products stimulate plant systems that lead to increased root mass, leaf area, fruiting and early maturation"

3. "The result is healthier plants and higher and better quality yields in a wide variety of crops."

4. "EDEN believes that products containing Harp-N-Tek(harpin) will revolutionize plant protection and crop production worldwide, empowering plants to be stronger, healthier, and more productive"

Simultaneous activation of natural plant systems is said to:⁸

1. "Enhance plant growth, crop yield and quality. "

2. "Protect against a broad array of viral, fungal and bacterial diseases, including some for which no effective treatment is currently available."

3. "Enhance resistance to attacks by insects, decreasing potential for damage. "

4. "Effectiveness across a wide array of crops."

Safety

The Environmental Protection Agency (EPA) confirms that Messengerâ breaks down rapidly in the environment and is harmless to both the environment and humans.⁹ When the EPA approves a pesticide or compound for use in the environment however it is only verifying that it is okay to use it. The EPA does not make any statement as to the accuracy of the information in regards to the effectiveness of the product. Whether or not the product, in this case Messengerâ , does what it is supposed to do is up the user to determine.

Result in Temperate Areas

A considerable amount of laboratory work has been done on Arabidopsis and tobacco cell cultures indicating that harpin proteins function to increase growth and decrease disease and insect damage. Plants grown outside have not been shown to react in exactly the same way as in the laboratory or in the greenhouse.

"Technical reports from university research, though not as thorough as published articles, still can provide useful and generally objective information. Most of the following field studies (unless indicated) are some from reports that Chalker-Scott was able to access over the Internet:¹⁰

A few other interesting comments from independent research institutions:

1)University of Arizona Yuma Agricultural Research Center: No significant effect on growth pattern or yield (Further investigation will be needed).

2)University of Georgia: "Tests in Georgia have shown no benefit in disease control."

3)University of Kentucky: "Harpin…has not performed well in replicated tests." "…no change in blue mold activity with increasing rate of Messenger® – strong evidence of the lack of efficacy of this product."

Concerns:

In review, there are a few factors that must be considered:

1. Chlorinated water must NOT be used.
2. To protect the plants from disease, they must be sprayed 5-7 days before the infection begins.
3. Some researchers have suggested that climatic conditions may effect the success of the treatment with areas which are warmer, wetter, and sunnier expected to show increased effect of the protein.
4. The compound is somewhat expensive.
5. Controlled laboratory experiments do not necessarily translate to greenhouse or field success especially in the northern areas.
6. Unless the specific plants have been field tested by an independent agency (with peer review), it would be unwise to conclude that any or all of the desired effects will be present.

What does this mean for us?

To my knowledge, no independent scientific studies have been done on daylilies. We must wait until scientific studies are done before we decide to treat all of our plants to improve growth or fight disease. For interested daylily growers, it might be good to do a test for yourself. Take a portion of your garden and treat it with Messenger® and use the other portion as a control to compare with the area that you treated. Please make sure that you examine any differences very carefully to determine whether or not you got enough of an increase in growth or decrease in disease to warrant the added expense of the treatment. For the best job of determining whether Messenger works on daylilies in this region, we must test it on large number of a single variety. The growth, flowering, etc. of the treated plants must be carefully compared with that of the untreated. Most of us do not have the numbers of a single variety to allow an accurate test but comparisons of similar varieties would be better than no test at all.

Don’t succumb to advertising hype – ask for objective, independent and balanced opinions. "If they are not available, take all "magic bullet" claims with a grain of salt."¹⁴ If a desired significant effect is found in a plant, one must determine if the added protein will produce enough of an effect to warrant the use of the expensive harpin compound. In conclusion, never take just the manufacturer’s or seller’s word for the functionality of any product.

ProAct is a new chimeric protein comprised of the active portions of the harpins produced by several different plant pathogenic bacteria. It is said to be 5 to 10-fold more active than Messenger® (on an equal weight basis) in tests conducted by Eden Bioscience.¹⁵ Maybe, just maybe, this will be the "magic bullet" of the future. It may be on the market in a few years. As ProAct is a protein, when it is in the environment it is a food source for many bacteria and fungi. I suspect that its actions, if any, on field grown plants will be much less than those grown under experimental conditions.

-----------------------------------------------------------------------

1. Wei,Zhongmin, et.al. 1992. "Harpin elicitor of the hypersensitive response produced by plant pathogen Erwinia amylovora". Science, Vol. 257, pp 85-88

2. Plant Vaccine Cure All http://www.wildlifenews.co.uk/articles2000/may/may0600b.htm

3. Margaret Tuttle McGrath http://counties.cce.cornell.edu/washington/ag/hort/CCEWash_Messenger.html

4. Protein Enables Plants To Resist Disease And Insects While Enhancing Growth, Cornell University http://www.sciencedaily.com/releases/2000/05/000501075158.htm

5. Stanton, Gill and Deborah Smith-Fiola. Stronger Plants Through "Harpin" Technology Grower talks http://www.gardeningthings.com/sm/cimpublic/retrieve.cgi?catalog_id=1.11.27

6. Protein helps plants resist disease, insects; http://www.news.cornell.edu/Chronicle/00/5.4.00/harpin.html

7. Eden Biotech http://www.edenbio.com/usa/technology/

8. http://www.gardeningthings.com/sm/cimpublic/retrieve.cgi

9. Blaine P. Friedlander Jr. EPA approves use of Cornell-discovered protein that enables plants to resist disease and insects while enhancing growth http://www.news.cornell.edu/releases/April00/FireBlight.bpf.html

10. Chalker-Scott, Linda. The myth of the Magic Bullet. http://www.puyallup.wsu.edu/~linda%20chalker-scott/Horticultural%20Myths_files/Myths/Harpin.pdf

11. http://www.hort.cornell.edu/extension/commercial/vegetables/online/2001veg/pdfs/text/EdenPeppers01.pdf http://www.hort.cornell.edu/extension/commercial/vegetables/online/2001veg/pdfs/text/EdenSweetcorn01.pdf

12. William C. Robertson and Brian Weatherford Evaluation of Messenger™ in Cotton http://www.uark.edu/depts/agripub/Publications/researchseries/507-32.pdf

13. Craig H. Canaday and Emily W. Gatch Effects of Messenger, Zoxium, and other fungicides on growth and diseases of fall spinachhttp://bioengr.ag.utk.edu/Extension/ExtProg/Vegetable/year/VegInitReport01/30effects_of_messenger.htm

14. Chalker-Scott, Linda. The myth of the Magic Bullet. http://www.puyallup.wsu.edu/~linda%20chalker-scott/Horticultural%20Myths_files/Myths/Harpin.pdf

15. Hudson Valley Horticulture~ Cornell Cooperative Extension of the Hudson Valley Commercial Horticulture Electronic Newsletter Volume5, Issue 8,August 8, 2005 http://counties.cce.cornell.edu/westchester/mastergardener/Hudson_Val_05/vol5_i8.htm#messenger

Home