Virulence characteristics of Bremia lactucae populations in Norway
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Use of resistant cultivars represent an efficient control measure for lettuce downy mildew (Bremia lactucae), although the durability of presently deployed resistance genes remains uncertain. Our objective was to document the pathogenic diversity of B. lactucae isolates in Norway. A total of 69 isolates of B. lactucae were collected between 2001 and 2006 from 65 commercial fields and four greenhouses in southeastern and southwestern Norway and tested for the presence of one or more of 19 virulence factors (v-factors). Phenotypic diversity was calculated based on presence or absence of v-factors, and as an overall comparison of v-phenotypes for each isolate. Disease severity varied over the years of the study, and epidemics were most consistently severe in southeastern Norway. The most commonly occurring v-factors, in order of frequency, were v5/8, v7, v2, v18, v4, v13, v6, v11, v12, v1 and v10. Virulence factor v17 was not found, while v36 was found in one isolate only. A total of 44 different v-phenotypes were identified within the population represented by the 69 isolates, yielding an incidence of unique virulence types of 63 %; a relatively high level of pathogen diversity. Four of the identified v-phenotypes were identical to races Bl:17, 18, 22 and 24, which have been previously reported in European populations of B. lactucae. The variability of the Norwegian B. lactucae populations verifies the genetic flexibility of this pathogen and its great ability to adapt to changes in host plants and surrounding conditions.
KeywordsEpidemiology Lactuca sativa Lettuce Lettuce downy mildew Race-specific resistance Virulence factors
We greatly appreciate the close cooperation with local advisors in the Norwegian Agricultural Extension Service who sampled the lettuce isolates. We also thank A. Hägnefelt, Swalöf Weibull, Sweden and I. Weber, Seminis Research, the Netherlands, and their colleagues for testing the B. lactucae isolates used in this study. Thanks also to T. Rafoss for statistical advice, and A. Stensvand for valuable comments on the manuscript. Figure 1 was kindly provided and adjusted by E. Fløistad. This study was part of a project funded by The Research Council of Norway, Innovation Norway and Norwegian lettuce growers.
- Andrivon, D. (1995). Comparison of race structure and diversity in populations of Phytophthora infestans, 1966–1993. In L. J. Dowley, E. Bannon, L. R. Cooke, T. Keane, & E. O’Sullivan (Eds.), Phytophthora infestans 150 (pp. 71–76). Dublin: Boole Press Ltd.Google Scholar
- Braz, L. T., Dalpian, T., & Pissardi, M. A. (2007). Identification of races of Bremia lactucae in São Paulo, Brazil. Acta Horticulturae, 760, 317–321.Google Scholar
- Crute, I. R., & Dixon, G. R. (1981). Downy mildew diseases caused by the genus Bremia Regel. In D. M. Spencer (Ed.), The downy mildews (pp. 423–460). London: Academic.Google Scholar
- Hermansen, A., & Myrstad, I. (1997). Salatbladskimmel (Bremia lactucae). Riktig sortsvalg er viktig for å unngå problemer. Gartneryrket, 95, 11–12 (In Norwegian).Google Scholar
- IBEB. (n.d.). The International Bremia Evaluation Board (IBEB). http://www.worldseed.org/isf/ibeb.html. Accessed 19 Nov 2013.
- Jönsson, B., Forsberg, A.-S., Hägnefelt, A., Paaske, K., & Svedelius, G. (2005). A co-operative project to create a strategy for controlling lettuce downy mildew (Bremia lactucae) in iceberg lettuce in Scandinavia. IOBC wprs Bulletin, 28(4), 145–152.Google Scholar
- Jørstad, I. (1964). The phygomycetous genera Albugo, Bremia, Plasmopara and Pseudoperonospora in Norway, with an appendix containing unpublished finds of Peronospora. Nytt Magasin for Botanikk, 11, 47–82.Google Scholar
- Lebeda, A., & Schwinn, F. J. (1994). The downy mildews—an overview of recent research progress. Journal of Plant Diseases and Protection, 101, 225–254.Google Scholar
- Lebeda, A., & Syrovátko, P. (1988). Specificity of Bremia lactucae isolates from Lactuca sativa and some Asteraceae plants. Acta Phytopathologica et Entomologica Hungarica, 23, 39–48.Google Scholar
- Lebeda, A., Pink, D. A. C., & Astley, D. (2002). Aspects of the interactions between wild Lactuca spp. and related genera and lettuce downy mildew (Bremia lactucae). In P. T. N. Spencer-Phillips, U. Gisi, & A. Lebeda (Eds.), Advances in downy mildew research (pp. 85–117). Dordrecht: Kluwer Academic Publishers.CrossRefGoogle Scholar
- Maisonneuve, B., Jeuniaux, S., Julliard, E., & Lovera, M. (2011). Virulence of Bremia lactucae populations in Southern France between 2006 and 2011. In S. van Heusden (Ed.), EUCARPIA leafy vegetables 2011. Book of abstracts of the Eucarpia leafy vegetables 2011 conference (p. 24). Villeneuve d’Ascq: Université Lille Nord de France.Google Scholar
- Nordskog, B. (2006). Studies on the epidemiology of lettuce downy mildew (Bremia lactucae Regel), including a survey of fungal pathogens in field lettuce (Lactuca sativa L.) in Norway. Norwegian University of Life Sciences. PhD Thesis 2006:24.Google Scholar
- Nordskog, B., & Hermansen, A. (2007). Virulence characteristics of Bremia lactucae populations present in Norway from 2001 to 2005. In A. Lebeda & P. T. N. Spencer-Phillips, (Eds.). Advances in downy mildew research, Vol. 3. Proceedings of The 2nd International Downy Mildews Symposium (pp.195–1998). v.o.s., Kostelec na Hané (Czech Republic): Palacký University in Olomouc and JOLA (ISBN 80-86636-19-4).Google Scholar
- Nordskog, B., Gadoury, D. M., Brurberg, M. B., Sivertsen, T. H., Kennedy, R., & Hermansen, A. (2008b). Investigating the inoculum source for downy mildews in onion, lettuce and cucumber in Norway. Journal of Plant Pathology, 90, S2.167.Google Scholar
- Reinink, K. (1999). Lettuce resistance breeding. In A. Lebeda & E. Kristkova (Eds). Eucarpia Leafy Vegetables ’99. Proceedings of the Eucarpia meeting on leafy vegetables genetics and breeding (pp. 139–147). European Association for Research on Plant Breeding. Olomouc (Czech Republic), Palacky University.Google Scholar
- Van Ettekoven, K., & van der Arend, A. J. M. (1999). Identification and denomination of “new” races of Bremia lactucae. In A. Lebeda & E. Kristkova (Eds.). Eucarpia Leafy Vegetables ’99. Proceedings of the Eucarpia meeting on leafy vegetables genetics and breeding (pp. 171–176). European Association for Research on Plant Breeding. Olomouc (Chez Republic), Palacky University.Google Scholar