Resistance and Virulence Structure in Two Linum marginale-Melampsora lini Host-Pathogen Metapopulations with Different Mating Systems

Abstract

Different patterns of resistance to six pathotypes of Melampsora lini were detected in 11 populations of Linum marginale distributed across two metapopulations. The two metapopulations (mountains and plains of New South Wales, Australia) differed in the annual cycle of disease development, which barely overlapped, and in the growth cycle and mating system of the host. Host populations in the mountains metapopulation were highly inbred, whereas those on the plains showed appreciable levels of outcrossing. Within each metapopulation there was significant variation among component populations in (1) levels of host resistance to individual pathogen isolates; (2) mean levels of resistance to all six isolates; (3) the number of resistance phenotypes present and the evenness of their distribution within the population; and (4) the average number of pathogen lines to which individual hosts were resistant. A more limited comparison of pathogen populations from the two metapopulations (two from each) found greater similarities in the structure of populations and particular virulence frequencies within, rather than among, the two metapopulations. Differences in host outcrossing rates between the two metapopulations are reflected in marked differences in the overall level of resistance, its partitioning within and among populations, the number and distribution of resistance phenotypes in the two areas, and the level of polymorphism for specific virulence factors in the pathogen, with the plains meta population showing consistently higher values. However, these differences were not significant. In general, variation for all parameters was just as great among populations within a metapopulation as between the two metapopulations.

The arms race is ancient history in Arabidopsis, the wildflower

“…It will be interesting to determine whether genetic variation in R genes is predominantly maintained by combining many R genes in the same genotype, or by assorting functional genes into simple genotypes and maintaining them in heterogeneous populations. The latter has been suggested by two studies of wild groundsel (Senecio vulgaris) and flax 55,56 . Detailed molecular genetic analyses have yet to be pursued in these pathosystems; however, functional NB-LRR genes already characterized in flax provide exciting examples for future studies of wild flax populations.…”

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

“…Such among-population processes might promote loss of genetic diversity within parasite populations and generate among-population genetic differences (e.g. through genetic drift), as has been observed for the biotrophic rust pathogen Melampsora lini infecting wild Australian flax Linum marginale , which is typified by ‘boom-and-bust’ epidemic dynamics [23,24]. By contrast, pathogens able to infect multiple hosts or survive in the absence of a host are unlikely to regularly experience such extreme levels of population stochasticity, and thus should maintain comparatively higher levels of within-population genetic variation.…”

Spatial variation in disease resistance: from molecules to metapopulations

“…In the interaction between L. marginale and M. lini , populations of Linum located in the mountains and plains regions of New South Wales of Australia are separated by several hundred kilometres. Detailed studies of host resistance structure within and between these regions showed large differences in average resistance, both among populations within the mountains and plains areas, as well as between regions (Burdon et al 1999). Levels of within-family heterogeneity in disease resistance in the mountain populations were low while heterogeneity within family lines was much more frequent in the plains.…”