ALBERT

Description: Background: Adaptation of pathogens to their hosts depends critically on factorsaffecting pathogenreproductive rate. While pathogen reproduction is the end result of an intricate interactionbetween host and pathogen, the relative contributions of host and pathogen genotype tovariation in pathogen life history within the hostare not well understood. Untangling thesecontributions allows us to identify traits withsufficient genetic variation for selection to actand to identify mechanisms of coevolution between pathogens and their hosts. Weinvestigated the effects of pathogen and host genotype on three life-history components ofpathogen fitness; infection efficiency, latent period, and sporulation capacity, in the oatcrown rust fungus, Puccinia coronata f.sp. avenae, as it infects oats (Avena sativa). Results: We show that both pathogen and host genotype significantly affect total spore productionbutdo so through their effects on different life-history stages. Pathogen genotype has thestrongest effect on the early stage of infection efficiency, while host genotype most stronglyaffects the later life-history stages of latent period and sporulation capacity.In addition, hostgenotype affected the relationship between pathogen density and the later life-history traitsoflatent period and sporulation capacity. We did not find evidence of pathogen-by-hostgenotypic (GxG) interactions. Conclusion: Our results illustrate mechanisms by which variation in host populationswill affect theevolution of pathogen lifehistory. Results show that differentpathogen life-history stages havethe potential to respond differently to selection by host or pathogen genotypeand suggestmechanisms of antagonistic coevolution. Pathogen populations may adapt tohost genotypethrough increased infection efficiency while their plant hosts may adapt by limiting the laterstages ofpathogen growthand spore production within the host.