The Leptosphaeria maculans – Leptosphaeria biglobosa species complex in the American continent |
| |
| Authors: | A Dilmaghani M H Balesdent J P Didier C Wu J Davey M J Barbetti Hua Li O Moreno-Rico D Phillips J P Despeghel L Vincenot L Gout T Rouxel |
| |
| Institution: | INRA-BIOGER, Av. Lucien Brétignières, BP 01, 78850 Thiverval-Grignon, France;;Cargill Inc., 2540 East Drake Road, Fort Collins, CO 80521, USA;;Monsanto Canada Inc., 3-75 Scurfield Blvd., Winnipeg, Manitoba R3Y 1P6, Canada;;School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley, W.A. 6009, Australia;;Microbiology Department, Universidad Autónoma de Aguascalientes, C.P. 20100, Aguascalientes, Ags., Mexico;;Department of Plant Pathology, UGA Griffin Campus, 1109 Experiment Street, Griffin, Georgia 30223, USA;;Monsanto S.A.S, Centre de Recherche de Boissay, 28310 Toury;;and AgroParisTech, Pathologie Végétale et Protection des Plantes, 75231 Paris Cedex 05, France |
| |
| Abstract: | Stem canker of oilseed rape (canola, Brassica napus ) is associated with a species complex of two closely related fungal species, Leptosphaeria maculans and L. biglobosa . Of these, L. maculans is the most damaging and develops gene-for-gene relationships with the host . Here, a wide scale analysis of the L. maculans - L. biglobosa species complex was performed throughout the American continent (23 locations from Chile to Canada) plus several locations in Western Australia for comparison purposes, based on a collection of 1132 isolates from infected tissues of a susceptible cultivar. Fungal species were discriminated on the basis of morphological, phytopathological and molecular criteria and showed that L. biglobosa was closely associated with L. maculans in most of the locations. Multiple gene phylogeny using sequences of ITS, actin and β-tubulin confirmed the prevalence of the L. biglobosa 'canadensis' sub-clade in Canada, whereas up to three different sub-clades of L. biglobosa were found in Georgia (USA). Race structure of L. maculans was investigated using a combination of pathogenicity tests and PCR amplification of avirulence alleles AvrLm1 , AvrLm4 and AvrLm6 . Three contrasting situations were observed: (i) race structure in Ontario, Chile and Georgia was related to that of European and Western Australian populations, with a low race diversity; (ii) only one race was found in Mexico, and not found outside of this country; (iii) a large diversity of races was observed in central Canada (Manitoba, Alberta and Saskatchewan) with very specific features including maintenance of avirulence alleles absent from Europe, absence of the AvrLm7 allele common in Europe (or eastern Canada) and wide location-to-location variability. |
| |
| Keywords: | avirulence Brassica napus molecular phylogeny population structure stem canker of oilseed rape |
|
|
