Centre for Plant Biodiversity Research

Changed patterns of resistance in a population of Linum marginale attacked by the rust pathogen Melampsora lini

J.J. Burdon and John N. Thompson*

Centre for Plant Biodiversity Research, G.P.O. Box 1600, Canberra, A.C.T. 2601 Australia.

*Departments of Botany and Zoologv, Washington State University, Pullman, W.A. 99164-4238 USA.

Summary

1 Various resistance phenotypes of L. marginale can he identified according to their responses to nine distinct phenotypes of the rust fungus M. lini. The relative frequency of these phenotypes was monitored on an 8-m x 8-m permanent plot established at Kiandra in southern New South Wales, Australia.

2 Over the period 1986-92 there was a marked change in the resistence structure of this population. This change was particularly associated with a major epidemic of rust occurring in the stance of 1989. The dominance of the host population by three resistance phenotypes prior to the epidemic was subsequently lost.

3 A similar change in resistance structure was detected in random samples taken in 1981 and 1991 from a different part of the same population. The changes in resistance in both the random-sample and the permanent plots were of no obvious adaptive value.

4 The distribution of the commonest resistance phenotypes on the permanent plot originally showed distinct patterns of aggregation which disappeared after the 1989 epidemic.

5 It is possible that the changing frequencies of particular resistance phenotypes could be explained by linkage between resistance genes and other traits that are under more intense selection. Alternitively, the changing frequencies could result from the combined effects of the presence of a pathogen pathotype which is, at least at certain locations, virilent on all host phenotypes, recruitment patterns in the host population and low pathogen transmission efficiencies.

Keywords: disease resistance, epidemic, host pathogen interactions, nonadaptive evolution, phenotypes, resistance genes

Published in: Journal of Ecology (1995) 83, 199-206.

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Updated 15 November, 1999 by Andrew Lyne