Pathogenicity, vegetative compatibility, and genetic diversity of verticillium dahliae isolates from sugar beet

Authors: Strausbaugh, Carl; Eujayl, Imad; Martin, Frank

Submitted to: Canadian Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2016
Publication Date: 12/22/2016
Publication URL: http://handle.nal.usda.gov/10113/5608162
Citation: Strausbaugh, C.A., Eujayl, I.A., Martin, F.N. 2016. Pathogenicity, vegetative compatibility, and genetic diversity of verticillium dahliae isolates from sugar beet. Canadian Journal of Plant Pathology. 38(4):492-505.

Interpretive Summary: Verticillium wilt of sugar beet is a disease problem that has received very little attention in the literature, but has been reported to reduce sucrose production and purity. To improve our understanding of the disease, a survey of sugar beet plants with wilt symptoms in Idaho was conducted in 2007 and 2008. Verticillium (V.) dahliae was found in 95% of the Idaho sugar beet fields and isolated from all plants with wilt symptoms. Fusarium oxysporum was also isolated from 19 to 21% of the symptomatic plants, but was later determined to be non-pathogenic. The V. dahliae sugar beet isolates all had the MAT1-2 mating type and 95% of the V. dahliae isolates belonged to vegetative compatibility group (VCG) 4A. All the VCG 4A isolates had the same mitochondrial haplotype based on sequencing of the cox3 to nad6 and cox1 to rnl loci. In greenhouse pathogenicity tests on sugar beet cultivar ‘Monohikari', the VCG 4A isolates produced more foliar symptoms than VCG 1, 1A, 2A, 2B, 3, and 4B isolates, but none of the VCGs consistently reduced root and top weight. The V. dahliae VCG 4A strains appear to be the primary cause of sugar beet wilt symptoms in Idaho, which is also true for Verticillium wilt of potato in North America. Therefore, rotating sugar beet with potato could be a concern since inoculum could buildup in a field, but unlike potatoes, sugar beet plants do not seem to die from infection.

Technical Abstract: Verticillium wilt of sugar beet is a disease problem that has received very little attention in the literature, but has been reported to reduce sucrose production and purity. To improve our understanding of the disease, a survey of sugar beet plants with wilt symptoms in Idaho was conducted in 2007 (5 roots from each of 40 fields; 200 roots total) and 2008 (5 roots from each of 45 fields; 225 roots total). Verticillium dahliae was isolated from all plants, while Fusarium oxysporum was isolated from 19 and 21% of the plants in 2007 and 2008, respectively. From a collection of 106 V. dahliae sugar beet isolates, all isolates had the MAT1-2 mating type and 95% evaluated for vegetative compatibility group (VCG) were 4A, while 1, 1, and 3% were non-compatible, VCG 4B, and VCG 2B, respectively. All the 4A isolates had the same mitochondrial haplotype based on sequencing of the cox3 to nad6 and cox1 to rnl loci. In greenhouse pathogenicity tests on sugar beet cultivar ‘Monohikari', the VCG 4A isolates produced more foliar symptoms (P < 0.0001) than VCG 1, 1A, 2A, 2B, 3, and 4B isolates, but none of the VCGs consistently reduced root and top weight. Since V. dahliae VCG 4A strains have also been documented to be the primary cause of Verticillium wilt in potato in North America, rotating sugar beet with potato could be a concern, but unlike potatoes, sugar beet plants do not seem to die from infection.