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ARS Home » Pacific West Area » Corvallis, Oregon » Horticultural Crops Research Unit » Research » Publications at this Location » Publication #225040
Title: Population Structure, Races, and Host Range of Aphanomyces euteiches from Alfalfa Production Fields in the Central U.S.A.

Author
item MALVICK, D - UNIVERSITY OF MINNESOTA
item Grunwald, Niklaus - Nik
item DYER, A - MONTANA STATE UNIVERSITY

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/7/2008
Publication Date: 2/2/2009
Citation: Malvick, D.K., Grunwald, N.J., Dyer, A.T. 2009. Population structure, races, and host range of Aphanomyces euteiches from alfalfa production fields in the central U.S.A. European Journal of Plant Pathology. 123(2):171-182.

Interpretive Summary: Aphanomyces euteiches is a plant pathogen causing root rot of alfalfa. The distribution and abundance of this pathogen is poorly understood in most areas of the United States, including Illinois where alfalfa is a major crop. This pathogen occurs in two races, race 1 and race 2, commonly found in alfalfa fields. Objectives of this study were to characterize the distribution and frequency of the races in alfalfa fields, determine host range on cultivated and native legumes, and describe populations of the pathogen in alfalfa fields. Both races were detected in 61% of Illinois counties, whereas only race 1 was detected in 22% and race 2 in 17%. Fourteen hosts for isolates from alfalfa fields were identified, and in addition to known hosts, eight new legume hosts were found to be susceptible to infection: kura clover, purple prairie clover, white prairie clover, ladino clover, hairy vetch, Canadian milk vetch, Illinois tick trefoil, and partridge pea. Populations of A. euteiches in alfalfa fields are diverse and often composed of both races 1 and 2.

Technical Abstract: Aphanomyces euteiches (races 1 and 2) cause root rot of alfalfa; however, its population biology and distribution were poorly understood in areas of the United States such as Illinois where alfalfa is a major crop. Objectives of this study were to (i) characterize the distribution and frequency of the races in alfalfa fields, (ii) determine host range on cultivated and native legumes, and (iii) describe genetic diversity and population genetic structure. To accomplish this, soil samples (n=103) were collected from 30 fields in 18 alfalfa producing counties of Illinois. Using the susceptible cultivar 'Saranac’, 148 isolates of A. euteiches were baited from the soil. The virulence phenotype of isolates representing all 18 counties was tested, and 54% were R1 and 46% were R2. Both races were detected in 61% of the counties, whereas only R1 was detected in 22% and R2 in 17%. Fourteen hosts for isolates from alfalfa fields were identified based on symptoms and/or production of oospores in roots. In addition to known hosts, eight legumes were susceptible to infection: kura clover, purple prairie clover, white prairie clover, ladino clover, hairy vetch, Canadian milk vetch, Illinois tick trefoil, and partridge pea. AFLP analysis revealed high levels of genetic diversity among the isolates from different fields and counties and a lack of genetic structuring of populations based on race or geographical origin. Populations of A. euteiches in alfalfa fields are diverse, often composed of races 1 and 2, and create risk for alfalfa with resistance to only one race and to multiple cultivated and native legume species.