Genetic structure of a population of the fungus Leptosphaeria maculans in a disease nursery of Brassica napus in Australia
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Microsatellite, minisatellite and mating type markers were used to determine the genetic structure of the fungus Leptosphaeria maculans within a disease nursery, where Brassica napus lines were screened for resistance to blackleg disease under high inoculum pressure. Fungal isolates were collected from pseudothecia in infected stubble and pycnidia within cotyledon lesions on seedlings within the nursery. Genetic diversity was high with gene diversity at H=0.700 across four polymorphic loci, and genotypic diversity at D=0.993. Among the 159 isolates analysed, 102 multilocus genotypes were identified. The even distribution of mating type idiomorphs MAT1-1 and MAT1-2 and gametic equilibrium within the population provided further evidence of random mating. Genetic diversity was distributed on a very fine scale in the disease nursery. The majority of genetic diversity (67%) was distributed among conidia within a lesion or among ascospores from a piece of stubble, while the remainder (33%) was distributed within lesions on seedlings or different stubble pieces. There were no among-group differences between samples from stubble and seedlings. This is consistent with the low level of genetic differentiation between the ascospore and conidia samples (FST=0.017) indicating that all isolates of L. maculans from the disease nursery most likely belong to one population, and that ascospores form the primary inoculum in the disease nursery.
KeywordsPhoma leaf spot Phoma lingam Microsatellite Population genetics Brassica napus
We thank Eugene Crozier and Athol Whitten for technical assistance, Dr Stephen Marcroft and Susan Sprague for assistance with the collection of infected plant material and anonymous reviewers for their comments. This research was supported by the Grains Research and Development Corporation.
- Armour JAL, Alegre SA, Miles S, Williams LJ, Badge RM (1999) Minisatellites and mutation processes in tandemly repetitive DNA. In: Goldstein DB, Schlötterer C (eds) Microsatellites: evolution and applications. Oxford University Press, Oxford, pp 24–33Google Scholar
- Bokor A, Barbetti MJ, Brown AG, McNish GC, Wood PM (1975) Blackleg of rapeseed. J Agric West Aust 16:7–10Google Scholar
- Goudet J (1995) FSTAT (Version 1.2): a computer program to calculate F-statistics. J Hered 86:485–486Google Scholar
- Holm S (1979) A simple sequentially rejective multiple test procedure. Scand J Stat 6:65–70Google Scholar
- Howlett BJ (2004) Current knowledge of the interaction between Brassica napus and Leptosphaeria maculans. Can J Bot 26:245–252Google Scholar
- van Kan JAL, van den Ackerveken GFJM, de Wit PJGM (1991) Cloning and characterization of cDNA of avirulence gene avr9 of the fungal pathogen Cladosporium fulvum, causal agent of tomato leaf mould. Mol Plant Micro Interact 4:52–59Google Scholar
- Koch E, Song K, Osborn TC, Williams PH (1991) Relationship between pathogenicity and phylogeny based on Restriction Fragment Length Polymorphism in Leptosphaeria maculans. Mol Plant Micro Interact 4:341–349Google Scholar
- Pielou EC (1969) An introduction to mathematical ecology. Wiley, New YorkGoogle Scholar
- Raymond M, Rousset F (1995a) GENEPOP (Version 1.2): a population genetics software for exact tests and ecumenicism. J Hered 86:248–249Google Scholar
- Wright S (1951) The genetical structure of populations. Ann Eugen 15:323–354Google Scholar