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Genetic structure of populations of Alternaria brassicicola suggests the occurrence of sexual recombination

Published online by Cambridge University Press:  28 February 2005

Clive H. BOCK
Affiliation:
CSIRO-Plant Industry, Centre for Plant Biodiversity Research, GPO 1600, Canberra, ACT 2601, Australia. E-mail: cbock@ushrl.ars.usda.gov Present address: Subtropical Plant Pathology Research Unit, USDA-ARS, USHRL, 2001 South Rock Road, Fort Pierce, Florida 34945, USA.
Peter H. THRALL
Affiliation:
CSIRO-Plant Industry, Centre for Plant Biodiversity Research, GPO 1600, Canberra, ACT 2601, Australia. E-mail: cbock@ushrl.ars.usda.gov
Jeremy J. BURDON
Affiliation:
CSIRO-Plant Industry, Centre for Plant Biodiversity Research, GPO 1600, Canberra, ACT 2601, Australia. E-mail: cbock@ushrl.ars.usda.gov
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Abstract

Substantial polymorphism was detected between isolates from five populations of Alternaria brassicicola attacking Cakile maritima along the New South Wales coast of Australia, with a maximum of two genotypes being shared between population pairs. Of ten pair-wise population comparisons, six had no pathogen genotypes in common; only one genotype occurred five times, and most (93%) were found only once. Although an UPGMA based on Nei's measure of genetic distance separated the five populations, a cluster analysis using individual isolates failed to group them according to population, indicating significant gene flow. An analysis of molecular variance indicated ca 14% of the variation occurred between populations, representing moderate population differentiation over the spatial scale of the study. Tests of the relative contribution of clonality and sexual recombination indicated low, albeit significant levels of linkage disequilibrium in all populations. The level of linkage disequilibrium, and the high genotype diversity, provides support for the contention that a hitherto unidentified sexual stage might be a significant factor in the life-cycle of A. brassicicola.

Type
Research Article
Copyright
© The British Mycological Society 2005

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