Specialization and Local Adaptation of a Fungal Parasite on Two Host Plant Species as Revealed by Two Fitness Traits

Abstract

We investigate the geographic pattern of adaptation of a fungal parasite, Colletotrichum lindemuthianum, on two host species, Phaseolus vulgaris and P. coccineus for two parasite fitness traits: infectivity (ability to attack a host individual) and aggressivity (degree of sporulation and leaf surface damage). Using a cross-inoculation experiment, we show specialization of the fungus on its host species of origin for both traits even when fungi, which originated from hosts growing in sympatry, were tested on sympatric host populations. Within the two host species, we compared infectivity and aggressivity on local versus allopatric plant-fungus combinations. We found evidence for local adaptation for the two traits on P. vulgaris but not on P. coccineus. There was no significant correlation between the degrees of local adaptation for infectivity and aggressivity, indicating that the genetic basis and the effect of selection may differ between these two traits. For the two fitness traits, a positive correlation between the degree of specialization and the degree of local adaptation was found, suggesting that specialization can be reinforced by local adaptation.

Distance- and density-dependent seedling mortality caused by several diseases in eight tree species co-occurring in a temperate forest

“…Although little is known of the causal relationships between infectivity and host mortality in most of the individual fungal species, particularly for host tree species (but see Sahashi et al 1995;Packer and Clay 2000;Augspurger and Wilkinson 2007;Seiwa et al 2008), the observed distant-dependent attacks by the predominant diseases (including several fungi) may suggest that generalist pathogens with broad host ranges may cause seedling mortality in a host-specific manner in this forest community. Recently, Sicard et al (2007) found that both infectivity and the degree of leaf damage by the pathogen Colletotrichum lindemuthianum differed among individual host populations and among host plants, because the pathogens were adapted to the local genotypes of the host plant. Our results, together with evidence of local adaptation (Sicard et al 2007) and negative feedback (Packer and Clay 2004;Kotanen 2007), may suggest that some soilborne pathogens are ubiquitous, but infectiousness and virulence of the pathogens are frequently higher beneath conspecific adults, because generalist pathogens sometimes adapt specifically to their local host populations (Bever 1994;Bever et al 1997;Mills and Bever 1998;Lively and Dybdahl 2000).…”

“…Recently, Sicard et al (2007) found that both infectivity and the degree of leaf damage by the pathogen Colletotrichum lindemuthianum differed among individual host populations and among host plants, because the pathogens were adapted to the local genotypes of the host plant. Our results, together with evidence of local adaptation (Sicard et al 2007) and negative feedback (Packer and Clay 2004;Kotanen 2007), may suggest that some soilborne pathogens are ubiquitous, but infectiousness and virulence of the pathogens are frequently higher beneath conspecific adults, because generalist pathogens sometimes adapt specifically to their local host populations (Bever 1994;Bever et al 1997;Mills and Bever 1998;Lively and Dybdahl 2000). However, we compared pathogenicity between distances for predominant disease symptoms (including several fungi; Appendix 3), instead of individual fungi.…”

“…If herbivores or pathogens attack in a distance-or density-dependent manner without host specificity, all tree seedlings co-occurring with the focal species (even under heterospecific adults) would also be affected by generalist pathogens when total seedling density is high. Several studies have recently examined the virulence of pathogens beneath parents that more strongly affect seedlings through negative feedback mechanisms or local adaptation, not only in herbaceous and grassland communities (Bever 1994;Bever et al 1997;Mills and Bever 1998;Lively and Dybdahl 2000;Sicard et al 2007) but also in forest communities Clay 2000, 2004;Hood et al 2004;Reinhart et al 2005;Seiwa et al 2008). If locally adapted parasites infect a maximum number of local hosts depending on the host population density (Kirchner and Roy 2002;Dybdahl and Storfer 2003), disease infectivity and consequent seedling mortality will be higher beneath compared with far from conspecific adults.…”

Spatial variation in disease resistance: from molecules to metapopulations

“…2002; Laine 2005; Niemi et al . 2006; Sicard et al 2007; Springer 2007) (but see Kaltz et al . 1999 for an exception), and from classic boom-and-bust cycles, particularly in agricultural crops, where newly deployed resistance genes increase in frequency but then rapidly lose their effectiveness as pathogens adapt to that new variety (Browning & Frey 1969).…”

Pathogen and host genotype differently affect pathogen fitness through their effects on different life-history stages

“…Host and pathogen genotypic interaction effects (GxG interactions) can play a key role in pathogen adaptation to sympatric host genotypes [31-34] as well. Local adaptation is expected in pathogens with dispersal ranges greater than their hosts [18], and there, GxG interactions of pathogen and host genotype may account for a large portion of the variation in pathogen reproductive rate.…”