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Oedema and Intumescences

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Intumescence on Cleome
Intumescence on Ipomoea (Sweet Potato Vine) 'Blackie'
Oedema on Ivy Geranium, leaf underside
Intumescence on greenhouse tomato

Intumescences are small, bump-like protrusions on the surface of leaves, petioles and stems of affected plants. Intumescences are commonly called oedema or edema however, while intumescences and oedema or edema are often used interchangeable, research shows that the symptoms are caused by different factors and plant physiological responses in different plants. These symptoms are often found on ivy geraniums, sweet potato vine (ipomoea), tomatoes, peppers, begonias, cacti, ferns, palms, pansy, cleome and cole crop vegetables like broccoli, cabbage and cauliflower. Some succulent plants such as jade and peperomia are particularly sensitive to conditions which lead to the development of these symptoms although almost any broadleaved plant may be affected. Current research points out that lesions on ivy geranium would be referred to as "oedema" while lesions on tomato and ornamental sweet potato would be referred to as "intumescence".

Oedema (edema) and intumescence are not caused by diseases like a bacterium, or a virus and are not transmittable from one plant to another. They are physiological disorders. Recent research indicates that light quality, specifically ultraviolet-B (UVB) radiation is directly related to preventing or minimizing intumescence symptoms on ornamental sweet potato and tomato, however has been found to have no effect on geraniums.

Symptoms on Ivy Geraniums

Photos of symptoms on various plants - New England Greenhouse Update Photo Gallery

According to research conducted by Kansas State University in 2009, oedema blisters form on ivy geraniums when water and solutes build up underneath or possibly within cells, causing the epidermal cells to stretch and collapse. The cells do not rupture as was previously thought.  Symptoms of oedema appear as bumps or blisters initially on the undersides of lower or older leaves on a plant. They may then turn brownish or tan and become corky. Severely affected leaves will often turn yellow and fall off the plant. The corky spots sometimes resemble spider mite or thrips damage. To rule out pest damage, growers are advised to use a handlens and check carefully on the undersides of leaves along midveins for spider mites and in growing points for thrips. Mildly affected plants often recover from oedema, putting out symptomless new growth in late spring and early summer. Some plants however are severely affected, have dropped significant numbers of leaves and have badly distorted remaining leaves. These plants are probably not worth saving as they will not recover in time for sale.

Research Results

Growers have been advised to fertilize ivy geraniums once every three feedings with calcium and potassium nitrate to thicken the cell walls to make plants more resistant to oedema. The research by Kansas State University reported that supplemental calcium did not have any effect on oedema on ivy geraniums in any of their experiments. Even more surprising, their studies showed that a range of root medium water contents did not have a marked effect on differences in oedema occurrence or severity. This is contrary to previous research reports about the cause of this disorder. Different transpiration rates resulting from dry versus optimal to saturated root medium water contents also had no affect on oedema occurrence on ivy geraniums in their study.

While many other researchers have suggested that water uptake that exceeds plant transpiration may contribute to causing oedema, this one study does not support this theory.

Previous Cultural Recommendations for Management

Previous studies reported that oedema on ivy geraniums occurred when the growing media remained warm and moist and the greenhouse air was cool and moist. The plant roots absorbed water at a faster rate than was transpired through leaf cells causing the leaf cells to rupture. This rupturing of the leaf epidermis and the inner cells caused the raised, crusty appearance on the underside of the leaf.

For many years, suggestions for managing oedema included: 

  • Using a well drained growing media
  • Increasing light intensity through spacing plants
  • Avoiding over-fertilizing, especially slow-growing plants, maintain a growing media pH of 5.5
  • Avoiding over- watering and growing on the "dry side" during extended periods of low light and cool temperature.
  • Reducing humidity by venting the greenhouse first thing in the morning, even if that means turning up the heat. Anything a grower could do to improve drainage and air circulation around plants was to help prevent edema.  See the article "Reducing Humidity in the Greenhouse" in the Nov./Dec.2003 issue of Floral Notes or on our website listed below.
  • When using containers that have snap-on saucers, delaying putting the saucer on until the crop is nearly finished.
  • Placing varieties with similar growth vigor on each irrigation line or section, again to eliminate over watering.

While these are good cultural recommendations, perhaps selecting ivy geranium cultivars that are resistant to oedema offers the best option at this time for growers to manage it!

Table 1. Ivy geranium varieties categorized by susceptibility to edema as published in 1993 in Geraniums IV .

Table 1. Susceptibility to edema
Most susceptible Intermediate Most resistant
Amethyst Madeline Crozy Sugar Baby
Yale Cornell Double Lilac White
Balcon Princess Spain Salmon Queen
King of Balcon Pascal Sybil Holmes
Balcon Imperial Rigi Galilee
Balcon Royale Rouletta  
Beauty of Eastborne    

Table 2. Observations of susceptibility of ivy geranium varieties to oedema, grown in the Rutgers University greenhouses in 1995. The plants were visually rated on a scale of 1-10 with 1 being highly susceptible and 10 indicating few symptoms. * These plants were grown and evaluated in a glass greenhouse.

Table 2. Susceptibility to edema *
Most susceptible Intermediate Most Resistant
Flare (3) Nicole (8) Vinco (9)
Charade (5) Blanche Roche (8) Van Gogh (9.5)
Lambada (6) Nico (8)  
Baroch (6) Pico (8)  
Bernardo (6) Amethyst (8)  

 

Intumescence Susceptibiltiy of Ornamental Sweet Potato Cultivars

In recent research by Kansas State University, ornamental sweet potato cultivars were screened for susceptibility to intumescences. Out of 36 cultivars tested, 19 did not show any symptoms of intumescence development. According to the research, susceptible cultivars included 'Blackie', 'Black Heart', 'Desana Bronze', 'South of the border chipotle', 'Sweet Caroline Bronze', 'Sweet Caroline Sweetheart Red' and 'Tricolor'. For information see the article: Intumescences: Further Investigations into an Elusive Physiological Disorder in the September 2014 issue of Greenhouse Product News Magazine.

References:

 

Compiled 11/04, Revised 2013, 2014
Topics: 
Commercial Horticulture
Commercial Horticulture topics: 
Crops
Diseases
Greenhouse Management