March 10, 2005
Source: American Phytopathological Society, Plant Disease Notes [edited]

First report of Fusarium oxysporum causing yellows on sugar beet in the Red River Valley of Minnesota and North Dakota
C. E. Windels and J. R. Brantner, University of Minnesota, NW Research and Outreach Center, Crookston 56716; and C. A. Bradley, Department of Plant Pathology, and M. F. R. Khan, Department of Soil Science, North Dakota State University, Fargo 58105. Plant Dis. 89:341, 2005; published on-line as DOI: 10.1094/PD-89-0341B. Accepted for publication 8 Dec 2004.

In 2002, some sugar beet (_Beta vulgaris_ L.) fields in the Red River Valley (RRV) of Minnesota and North Dakota had symptoms characteristic of Fusarium yellows (4). In 2004, approximately 5 percent of fields in the RRV had symptomatic plants. Interveinal yellowing of older leaves typically began in mid-July and as the disease progressed, younger leaves turned yellow. Sometimes, one side of the leaf was yellow or necrotic while the other side remained green. As leaves died, they remained attached to the crown.

Transverse sections of roots revealed a light gray-brown discoloration of the vascular tissue but no external rotting of roots. Isolations from 35 symptomatic roots collected in 8 fields yielded 25 isolates identified as _F. oxysporum_ (from single conidia grown on homemade potato dextrose agar and carnation leaf agar) (3).

Pathogenicity was determined by dipping roots of 5-week-old sugar beet plants (cv. ACH 9363) in a suspension of 10 000 conidia per ml for 8 min (12 isolates, 10 to 12 plants per isolate). Plants were planted in Cone-tainers (3.8 cm diameter x 21 cm; Stuewe and Sons, Inc. Corvallis, OR) containing sterile soil. 3 known cultures of _F. oxysporum_ Schlecht. emend. Snyd. & Hans. f. sp. _betae_ Stewart (= _F. conglutinans_ var. _betae_ Stewart [4]) also were included (13 and 216c from L. Hanson, USDA-ARS, Fort Collins, CO; 0-1122 from The Pennsylvania State University Fusarium Research Center). The control was sterile water. Plants were placed in a greenhouse at 24 to 27 deg C with natural light supplemented with illumination from high-pressure sodium-vapor lamps for 16 h daily and lightly fertilized biweekly to avoid chlorosis from nutrient deficiency.

After 6 to 7 weeks, plants were rated for disease on a 0 to 4 scale: 0 = no disease; 1 = slight to extreme plant stunting, leaves may be wilted; 2 = chlorotic leaves, some with necrosis at margins; 3 = tap root dried and brown to black in color, leaves dying; and 4 = plant dead (1). The experiment was repeated. Disease severity differed between trials, but all isolates of _F. oxysporum_ and _F. oxysporum_ f. sp. _betae_ resulted in disease ratings statistically (P < 0.05) greater than that of the water control.

In Trial 1, isolates of _F. oxysporum_ averaged a rating of 2.1 (range of 1.8 to 3.3) and _F. oxysporum_ f. sp. _betae_ averaged 2.1 (range of 2.0 to 2.2) compared with 0.1 for the water control. One isolate of _F. oxysporum_ had a statistically higher rating than did the cultures of _F. oxysporum_ f. sp. _betae_. In Trial 2, isolates of _F. oxysporum_ averaged a rating of 3.3 (range of 2.7 to 3.7) and _F. oxysporum_ f. sp. _betae_
averaged 3.1 (range of 2.7 to 3.4) compared with 0.2 for the water control.

Cultures of _F. oxysporum_ (8 of 12) resulted in ratings statistically higher than that of the least pathogenic culture of _F. oxysporum_ f. sp. _betae_. Cultures of _F. oxysporum_ and _F. oxysporum_ f. sp. _betae_ recovered from inoculated plants were identical to those used to inoculate plants.

To our knowledge, this is the 1st report of _F. oxysporum_ f. sp. _betae_ on sugar beet in the Red River Valley of Minnesota and North Dakota. The disease has been reported in California, Colorado, Montana, Nebraska, Oregon, Texas, and Wyoming (1,2).

References:

(1) R. A. Cramer et al. J. Phytopathol. 151:352, 2003.
(2) G. A. Fisher and J. S. Gerik. Phytopathology 84:1098, 1994.
(3) P. E. Nelson et al. Fusarium Species: An illustrated Manual for Identification. The Pennsylvania State University Press. University Park, 1983.
(4) D. Stewart. Phytopathology 21:59, 1931.

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[The fact that Fusarium yellows (FY), also known as Fusarium wilt, has been reported from the Red River Valley of Minnesota and North Dakota is not surprising, given the opportunity for propagules of the fungus to be distributed on windborne soil aggregates and by physical movement of soil on farm equipment. _F. oxysporum_ f. sp. _betae_ is the pathogen that causes FY. Disease management utilizes certified seed of Fusarium wilt-tolerant or resistant varieties, if available, treatment of seed or furrow with recommended fungicides to delay initial infection of seedlings by _Fusarium_ spp. and other soil-borne pathogens, manage irrigation to eliminate moisture stress to the developing plant, avoid excess water which may deprive roots of oxygen, and dispose of sugar beet tare soil to avoid introduction of FY propagules (or new races) into the field.

Link: <http://www.findarticles.com/p/articles/mi_qa4066/is_200311/ai_n9330576>
<http://www.ext.colostate.edu/pubs/crops/02950.html>
-Mod.DH]