Population structure, races, and host range of Aphanomyces euteiches from alfalfa production fields in the central USA

Abstract

Aphanomyces euteiches (races 1 and 2) causes root rot of alfalfa; however, its population biology and distribution are poorly understood where alfalfa is a major crop. The objectives of this study were to (1) characterise the distribution and frequency of races of A. euteiches in Illinois alfalfa fields, (2) determine host range of A. euteiches on cultivated and native legumes, and (iii) to describe genetic diversity and population genetic structure of A. euteiches in alfalfa fields. To accomplish this, soil samples (n= 103) were collected from 30 alfalfa fields in 18 Illinois counties. Using the susceptible cv. '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%. Thirteen legume hosts for isolates from alfalfa fields were identified based on symptoms and/ or production of oospores in roots. In addition to six previously known hosts, seven species were susceptible to infection: kura clover, purple prairie clover, white prairie clover, ladino clover, hairy vetch, Canadian milk vetch, and Illinois tick trefoil. 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. The results suggest that populations of A. euteiches in alfalfa fields are diverse, often composed of races 1 and 2, and create risk for alfalfa and to multiple cultivated and native legume species.

Genetic and Pathogenicity Diversity of Aphanomyces euteiches Populations From Pea-Growing Regions in France

“…A. euteiches is reported to attack other legume species including common bean, broad bean, faba bean, clover, and alfalfa (Pfender and Hagedorn, 1982 ; Lamari and Bernier, 1985 ; Tivoli et al, 2006 ; Moussart et al, 2008 ). In some regions of the United States, where pea and alfalfa crops were frequently included in cropping systems, populations of pea-infecting A. euteiches showed differentiation into sub-populations with differences in genotypes and virulence toward pea and alfalfa (Holub et al, 1991 ; Malvick et al, 1998 , 2009 ; Malvick and Grau, 2001 ). To investigate the presence of such distinct isolate genotypes, influenced by their host of origin in France, it would thus be necessary to increase the number of isolates sampled from the Bourgogne fields studied and from other fields with various legumes in their crop histories.…”

A local score approach improves GWAS resolution and detects minor QTL: application to Medicago truncatula quantitative disease resistance to multiple Aphanomyces euteiches isolates

“…On the other hand, the genetic architecture of QDR of M. truncatula seems to be governed by small-effect QDR loci in response to isolates Ae109, MF-1, and NC-1, which were reported to be pathogenic to a narrower host range, i.e., alfalfa and/or pea (Malvick et al 1998). The isolates Ae109, MF-1, and NC-1, originating from alfalfa production fields in the central United States (Malvick et al 2009), showed to be more adapted to M. truncatula, which is closely related to alfalfa, than the ATCC 201684 and RB84 isolates originating from pea growing areas in Europe.…”

Successive legumes tested in a greenhouse crop rotation experiment modify the inoculum potential of soils naturally infested by Aphanomyces euteiches

“…As suggested by Salt & Delanay (1985), the microflora or other biotic or abiotic soil factors may play an important role in root rot expression, and consequently could explain the lack of symptoms observed on alfalfa with naturally infested French soils. In contrast, aphanomyces root rot was reported in North American alfalfa fields, but the disease is due to specific isolates (Malvick et al. , 2009).…”