January 11, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of Fusarium graminearum causing dry rot of potato in North Dakota
S Ali, VV Rivera, GA Secor, Department of Plant Pathology, North Dakota State University, Fargo 58105. Plant Dis 2005; 89: 105, published online as DOI: 10.1094/PD-89-0105B. Accepted for publication 2 Oct 2004.

Fusarium dry rot of potato can be caused by several species of _Fusarium_, but _F. sambucinum_ is considered the primary cause in stored potatoes in North America and Europe (1).

Potato tubers of cvs. Shepody and Russet Burbank with severe dry rot were collected from a commercial processing storage facility in central North Dakota during 2003-2004. Pathogen isolations were made from infected tubers on one-half strength acidified potato dextrose agar (APDA). Only _F. graminearum_ was isolated from all rotted tubers used.

Identification was based on colony morphology and conidial and perithecial characteristics, which included a carmine coloration of the underside of the agar and white fluffy mycelium on APDA, the presence of black
perithecia on carnation leaf agar, and large distinctive macroconidia (2). The identity was confirmed by the Fusarium Research Institute at Pennsylvania State University. Pathogenicity was tested in potato tubers and greenhouse-grown potato plants cv. Atlantic.

9 tubers were wounded by removal of a plug of tissue with a cork borer, 3 mm in diameter and 5 mm deep, and inoculated by placing either 100 ul of a conidial suspension (50 000 conidia per ml) from a 7 day old culture or a
mycelial plug, 3 mm in diameter, from a 7 day old culture in the wound. 9 tubers wounded and treated with either sterile distilled water or one-half strength APDA served as controls.

Plant inoculations were performed by cutting a slit in the lower stem with a sterile scalpel and placing a cotton collar saturated with a conidial suspension (50 000 conidia per ml) around the wound and held in place with a clothespin. 4 plants were inoculated with a conidial suspension, and 4 plants were treated with sterile distilled water.

All tubers inoculated with either Fusarium treatment developed typical potato dry rot symptoms consisting of a brown dry decay with mycelium lined cavities, and _F. graminearum_ was reisolated from all symptomatic tubers.
The control tubers did not develop symptoms. No symptoms developed in any of the greenhouse inoculated plants.

15 isolates were tested for sensitivity to thiabendazole, and all were sensitive with EC(50) (50 per cent effective concentration) values ranging from 0.8 to 3.7 microliters/ml.

The results indicate that _F. graminearum_ can cause dry rot of potato, and, to our knowledge, this is the 1st report of _F. graminearum_ as a cause of potato dry rot.

These results have epidemiological implications in the persistence, spread, and management of _F. graminearum_ in cereals and potatoes, since potato is often used in rotation with other hosts of _F. graminearum_, including wheat, barley, and corn.

References:
1. GA Secor B Salas. Fusarium dry rot and fusarium wilt. In: WR Stevenson, R Loria, GD Franc, DP Weingartner (editors). Compendium of potato diseases.
2nd edition. St Paul, MN: American Phytopathological Society, 2001: pp 23-5. 2. PE Nelson, et al. Fusarium Species: An Illustrated Manual for Identification. University Park and London: Pennsylvania State University, 1983: pp 118-9.

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[In addition to _F. graminearum_, 2 other species (_F. avenaceum_ and _F. coeruleum_) have been reported to cause potato dry rot [DR]. DR usually causes extensive tissue decay and collapse, and large holes are common in tubers. The amount of DR due to decay in storage depends upon the amount of fungus in the soil, the extent of mechanical damage to tubers during digging and harvesting, and on the susceptibility of the potato variety.
Growers are advised to treat seed pieces with a recommended fungicide prior to planting, to make certain that tubers go into clean and disinfected storage bins, to handle treated seed with clean, disinfected equipment, to
harvest tubers during cool dry weather, and to prevent bruising during harvesting, handling and grading operations. Note that _F. graminearum_ was reported on soybean in Brazil last year (2004).

Links:
<http://vegetablemdonline.ppath.cornell.edu/factsheets/Potato_Fusarium.htm>
<http://www.ext.nodak.edu/extpubs/plantsci/rowcrops/pp1039w.htm>
<http://www.gov.mb.ca/agriculture/crops/diseases/fac44s00.html> - Mod.DH]