|Gulya Jr, Thomas|
|Gesch, Russell - Russ|
|Del Rio, Luis|
Submitted to: Disease Note
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/13/2006
Publication Date: 10/1/2006
Citation: Gulya Jr, T.J., Gesch, R.W., Bradley, C.A., del Rio, L.E., Johnson, B.L. 2006. First report of Sclerotinia sclerotiourum infection on Cuphea. Plant Disease Note. 90:1554. Available: http://www.apsnet.org/pd/searchnotes/2006/pd-90-1554a.asp Interpretive Summary: Cuphea is a genus of largely undomesticated species whose seed has recently been found to contain large quantities of fatty acids (oils) that may provide a domestic source of industrial lubricants, and thus minimize U.S. dependence upon foreign sources of these vegetable oils. Preliminary field trials have been planted in North Dakota and Minnesota to investigate potential yields and production practices. In 2004, several fields in western MN and eastern ND were observed to have patches of dead plants. The fungus killing these plants was identified as Sclerotinia sclerotiorum, a soilborne fungus with an extremely wide host range. Cuphea is the first genus in the family Lythraceae to be observed with this fungus. Since Sclerotinia is widely distributed in ND and MN, due to the frequent cropping of other susceptible hosts (beans, canola, soybeans, sunflower), soilborne sclerotia of this fungus will pose a threat to Cuphea production unless control measures can be found to minimize the disease.
Technical Abstract: Species of the genus Cuphea (family Lythraceae) are being developed as a potential domestic source of medium length fatty acids (lauric and capric) for use in industrial lubricants and detergents. Patches of dead plants were observed in test plots of Cuphea variety PSR-23 (1) (Cuphea viscosissima Jacq. x C. lanceolata W.T. Aiton) near Morris, Minnesota and Prosper, North Dakota, approximately 200 km apart, in September, 2004. Seed yield in the affected Morris field was 14 kg/ha compared to 85 kg/ha in nearby, unaffected fields, for an 85% yield reduction. Stems were split open to reveal long, cylindrical sclerotia up to 8 mm in length. Isolations from diseased stem tissue and from sclerotia both yielded Sclerotinia sclerotiorum, producing typical sized sclerotia (4-6 mm diameter) after seven days growth on potato dextrose agar. Cuphea PSR-23 plants were grown in the greenhouse in individual pots and inoculated when 5-wk old. Three inoculation methods were used. For the first method, ascospores of a sunflower isolate of S. sclerotiorum ascospores were sprayed onto blooming flowers and foliage at a rate of 5,000 spores/ml. The inoculated plants were kept in a dark, 18 C mist chamber for 48 hr and then returned to a greenhouse maintained at 24/20 C, day/night temperatures. All twenty inoculated plants were visibly colonized by Sclerotinia after 3 days, and all plants were dead by seven days. The second inoculation used the petiole inoculation technique employed by canola researchers (2). The blade from the third leaf was excised and a micropipette tip containing an agar disk of Sclerotinia mycelia (Cuphea isolate) was placed over the cut end of the petiole. Five days after inoculation all 30 inoculated plants were dead, while none of the 10 control plants (using sterile agar disks on the cut petiole were affected. Isolations were made from diseased plants inoculated with either mycelia or ascospores and S. sclerotiorum was reisolated. The third inoculation method tested root infection. S. sclerotiorum was grown on autoclaved millet [Pennisetum glaucum (L.) R. Br.] for 7 days, and 5 g of colonized millet was placed in a hole that was made 6 cm from the base of a Cuphea plant, with one plant per 3.7 liter pot. Sunflower (Helianthus annuus L.; oilseed hybrid Cargill 270) plants served as inoculated controls. None of the 20 Cuphea plants were infected via soil inoculations, compared to 70% of 30 sunflower plants which developed basal stalk rot and wilt within 2 wk after inoculation. This is the first report of S. sclerotiorum infection on Cuphea, and is believed to be the first report of infection on any genus within the Lythraceae.