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Genetic Dissection of Resistance to Anthracnose and Powdery Mildew in Medicago truncatula

¹UMR 5546 CNRS-UPS, Pôle de Biotechnologie Végétale 24 Chemin Borde Rouge, 34326 Castanet-Tolosan, France; ²Department of Plant Pathology, University of Minnesota, 495 Borlaug Hall, St. Paul 55108, U.S.A.; ³INRA, Unité de nutrition azotée des plantes, Versailles, 78026 France; ⁴United States Department of Agriculture--Agricultural Research Service, Plant Science Research, St. Paul, MN 55108, U.S.A.; ⁵Laboratoire Symbiose et Pathologie des Plantes (SP2) Pôle de Biotechnologie Végétale, 31326 Castanet-Tolosan, France

Medicago truncatula was used to characterize resistance to anthracnose and powdery mildew caused by Colletotrichum trifolii and Erysiphe pisi, respectively. Two isolates of E. pisi (Ep-p from pea and Ep-a from alfalfa) and two races of C. trifolii (races 1 and 2) were used in this study. The A17 genotype was resistant and displayed a hypersensitive response after inoculation with either pathogen, while lines F83005.5 and DZA315.16 were susceptible to anthracnose and powdery mildew, respectively. To identify the genetic determinants underlying resistance in A17, two F7 recombinant inbred line (RIL) populations, LR4 (A17 × DZA315.16) and LR5 (A17 × F83005.5), were phenotyped with E. pisi isolates and C. trifolii races, respectively. Genetic analyses showed that i) resistance to anthracnose is governed mainly by a single major locus to both races, named Ct1 and located on the upper part of chromosome 4; and ii) resistance to powdery mildew involves three distinct loci, Epp1 on chromosome 4 and Epa1 and Epa2 on chromosome 5. The use of a consensus genetic map for the two RIL populations revealed that Ct1 and Epp1, although located in the same genome region, were clearly distinct. In silico analysis in this region identified the presence of several clusters of nucleotide binding site leucine-rich repeat genes. Many of these genes have atypical resistance gene analog structures and display differential expression patterns in distinct stress-related cDNA libraries.

Additional keywords:biotrophic pathogen, disease, fungi, legumes.