Absence of isolation by distance patterns at the regional scale in the fungal plant pathogen Leptosphaeria maculans

Renaud Travadon (1) , Ivan Sache (2) , Christian Cyril Dutech (3) , Anna Stachowiak (2, 4) , Bruno Marquer (1) , Lydia Bousset (1)

1 BIO3P - Biologie des organismes et des populations appliquées à la protection des plantes
2 BIOGER - BIOlogie et GEstion des Risques en agriculture
3 BioGeCo - Biodiversité, Gènes & Communautés
4 Inst Plant Genet

Outcomes of host-pathogen coevolution are influenced by migration rates of the interacting species. Reduced gene flow with increasing spatial distance between populations leads to spatial genetic structure, as predicted by the isolation by distance (IBD) model. In wind-dispersed plant-pathogenic fungi, a significant spatial genetic structure is theoretically expected if local spore dispersal is more frequent than long-distance dispersal, but this remains to be documented by empirical data. For 29 populations of the oilseed rape fungus Leptosphaeria maculans sampled from two French regions, genetic structure was determined using eight minisatellite markers. Gene diversity (H = 0.62-0.70) and haplotypic richness (R = 0.96-1) were high in all populations. No linkage disequilibrium was detected between loci, suggesting the prevalence of panmictic sexual reproduction. Analysis of molecular variance showed that >97 % of genetic diversity was observed within populations. Genetic differentiation was low among populations (F(st) < 0.05). Although direct methods previously revealed short-distance dispersal for L. maculans, our findings of no correlation between genetic and geographic distances among populations illustrate that the IBD model does not account for dispersal of the fungus at the spatial scale we examined. These results indicate high gene flow among French populations of L. maculans, suggesting high dispersal rates and/or large effective population sizes, two characteristics giving the pathogen high evolutionary potential against the deployment of resistant oilseed rape cultivars.

Mots clés: gene flow; indirect measures; minisatellites; spatial genetic structure; spore dispersal; allele frequency data; in field populations; phoma stem canker; oilseed rape; genetic-structure; computer-program; demographic parameters; local adaptation; aerial dispersal; flux de gène; mesures indirectes; structure génétique; donnée de fréquence; population de fonds de terre; canola brassica napus

Domaines: Sciences du Vivant [q-bio]

Renaud Travadon, Ivan Sache, Christian Cyril Dutech, Anna Stachowiak, Bruno Marquer, et al.. Absence of isolation by distance patterns at the regional scale in the fungal plant pathogen Leptosphaeria maculans. Fungal Biology, 2011, 115 (7), pp.649-659. ⟨10.1016/j.funbio.2011.03.009⟩. ⟨hal-01189592⟩