Does selection by resistant hosts trigger local adaptation in plant–pathogen systems?

Abstract

Understanding the consequences of selection by host resistance on pathogen population structure provides useful insights into the dynamics of host–parasite co‐evolution processes and is crucial for effective disease management through resistant cultivars. We tested general vs. local population adaptation to host cultivars, by characterizing a French collection of Phytophthora infestans (the causal organism of potato late blight) sampled during two consecutive years on cultivars exhibiting various levels of resistance. Local populations were structured by the host for virulence (qualitative pathogenicity) but also for aggressiveness (quantitative pathogenicity). All populations had a low genotypic diversity for amplified fragment length polymorphisms (AFLPs), and presumably consisted of a few closely related clonal lineages. No correlation was detected between pathogenicity traits and AFLP genotypes. The data support the hypothesis of general adaptation for aggressiveness, to which directional selection for virulence is superimposed when race‐specific resistance is introduced.

Periodic host absence can select for higher or lower parasite transmission rates

“…10 11 Published data suggests that the transmission-virulence trade-off relationship operates in 12 several aerially and vector dispersed plant pathogens (Montarry et al 2006, Sacristan and 13 Garcia-Arenal 2008, Pariaud et al 2009b). The mode of survival between crop growing 14 seasons of this group of pathogens also leads to the presence of a transmission-survival trade-15 off.…”

Presence of the Potato Late Blight Resistance Gene <i>RB</i> Does Not Promote Adaptive Parasitism of <i>Phytophthora infestans</i>

“…Previous studies of P. infestans adaptation have focused on local populations and their interaction with the foliage of specific potato cultivars in the field [13,15,16,23]. The results of these studies propose different possible outcomes for adaptation to partially resistant hosts.…”

“…Although a promising source of long-term resistance, the durability of partial late blight resistance remains to be seen. Several reports have shown pathogen isolate specificity for partially resistant cultivars indicating adaptation that may result in the eventual breakdown of partial resistance [10][11][12][13][14][15][16]. However, the environmental conditions supporting adaptation to partially resistant cultivars remains uncertain since evidence suggests that pathogen populations are most likely to adapt to the most readily available host, regardless of environment or their resistance characteristics [15].…”

“…However, RB only confers partial resistance and allows the growth and sporulation of P. infestans to a small degree [19,20,22]. The partial resistance phenotype of plants expressing RB should not be confused with polygenic, partial resistance that has been described in several potato cultivars [13,15,16,23,24]. In these cases, several genes are thought to act together to provide an increased level of resistance whereas resistance mediated by RB acts in a gene-forgene manner [25].…”

The effect of CO2 and temperature on Fusarium crown rot incidence, severity, pathogen colonisation, toxigenic potential and host resistance in a selection of wheat germplasm

“…Pathogens can rapidly evolve new races in response to new resistant crop varieties by using a range of sexual and asexual mechanisms that generate new genetic variation (Fisher et al, 2012), sometimes after only three to five asexual cycles (Kolmer & Leonard, 1986). Host resistance also influences pathogen evolution (Montarry et al, 2006), and with large-scale agriculture the pathogen can rapidly evolve under continuous cropping of genetically uniform varieties .…”