Host-Pathogen Interactions in Natural Populations of Linum marginale and Melampsora lini: II. Local and Regional Variation in Patterns of Resistance and Racial Structure

Abstract

Spatial variation in the resistance structure of Linum marginale (wild flax) populations to the rust fungus Melampsora lini, and in the racial structure of this pathogen, was investigated by sampling 10 populations distributed throughout the Kosciusko National Park, New South Wales, Australia. Considerable differences were found among populations in the structure of both host and pathogen. Host populations were divided into three broad categories: (1) populations susceptible to all testing races; (2) populations containing a strictly limited number ofresistant phenotypes; and (3) populations with a considerable diversity ofresistant phenotypes. The pathogen populations also showed a range ofdiversity. The major differences between these populations were determined by the occurrence and frequency of four common races of pathogen (races A, E, K., and N). These differences were apparent both at a regional spatial scale (over the 100 km separation of the most distant populations) and at a local scale where major differences were detected between two populations only 300 m apart. The distribution of the four common races of M. lint was consistent with the hypothesis that a fitness cost was associated with unnecessary virulence. In general, however, differences in the structure of pathogen populations from genetically very similar host populations implied that, in addition to host resistance genes, other evolutionary forces are also important in determining the genetic structure of individual pathogen populations.

Coevolution of a Plant Host–Pathogen Gene-for-gene System in a Metapopulation Model without Cost of Resistance or Cost of Virulence

“…When the virulence allele is close to "xation, there is almost no selection operating on the resistance locus (Leonard, 1977), and consequently, we expect, the frequency of the resistance allele to be mainly controlled by genetic drift. But contrary to theoretical predictions, observations from natural populations of host} pathogen systems often show a high level of variation in both resistance and virulence loci (Parker, 1985;Burdon, 1987;Clarke et al, 1993;Jarosz & Burdon, 1991).…”

“…Natural plant populations have a patchy distribution, depending on where the environment is suitable for the host, and host}pathogen systems can be viewed as metapopulations comprising distinct subpopulations (Parker, 1985;Jarosz & Burdon, 1991;Burdon, 1993;Antonovics et al, 1994;Burdon et al, 1995). Host pollen or seeds and pathogen spores will migrate among the subpopulations, but the allele frequencies between neighboring subpopulations will not necessarily be equal if the migration rate is su$ciently low (Parker, 1985;Jarosz & Burdon, 1991).…”

Life history determines genetic structure and evolutionary potential of host–parasite interactions

“…[46,52]) and empirically. For example, high levels of virulence diversity within and between populations [53], local adaptation of pathogen and host populations [54], correlations between levels of host resistance and pathogen virulence in local populations, and tradeoffs between spore production and virulence [17] all implicate selection by L. marginale as an important source of variation in populations of M. lini . By contrast, genetically homogeneous crops grown over large areas impose strong directional selection on local pathogen populations, resulting in selective sweeps favouring particular genotypes and lower overall virulence diversity in pathogen populations [55].…”

Spatial variation in disease resistance: from molecules to metapopulations

“…Despite indications that R gene diversity may generally be high, for many wild plant-pathogen associations, some populations are found in which variation for disease resistance does not occur or is limited (Jarosz & Burdon 1991; de Meaux et al . 2003; Kniskern & Rausher 2006); while in others considerable intra-population diversity for resistance has been detected (Espiau et al .…”