Ecological and evolutionary implications of spatial heterogeneity during the off-season for a wild plant pathogen.
Bottom Line: We combined large-scale surveys and detailed experiments to investigate the overwintering success of the specialist plant pathogen Podosphaera plantaginis on its patchily distributed host plant Plantago lanceolata in the Åland Islands.Twelve years of epidemiological data establish the off-season as a crucial stage in pathogen metapopulation dynamics, with c. 40% of the populations going extinct during the off-season.We conclude that environmentally mediated changes in the distribution and evolution of parasites during the off-season are crucial for our understanding of host-parasite dynamics, with applied implications for combating parasites and diseases in agriculture, wildlife and human disease systems.
Affiliation: Metapopulation Research Group, Department of Biosciences, University of Helsinki, PO Box 65 (Viikinkaari 1), FI-00014, Helsinki, Finland.Show MeSH
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Mentions: The powdery mildew Podosphaera plantaginis (Castagne; U. Braun & Takamatsu) is a fungal plant pathogen specific to Plantago lanceolata L. Like all members of the powdery mildews (Erysiphaceae), it is an obligate pathogen requiring living host tissue throughout its life cycle. During the growing season, P. plantaginis grows on the surface of the plant, with only its feeding roots (haustoria) penetrating the epidermis. Wind-dispersed spores (conidia) are produced on chains growing vertically on the leaf surface. Over the winter, P. plantaginis survives (see the Results section) through specialized resting structures (i.e. chasmothecia, formerly cleistothecia; Braun et al., 2002). The resting structures of P. plantaginis are produced on the leaf surface (Supporting Information Fig. S1), and are relatively difficult to dislodge from the leaf (cf. Gadoury et al., 2010). The number of resting structures on an infected leaf in autumn can vary strongly, ranging from no or few resting structures up to several thousand (e.g. x-axis in Fig. 5a). During development, the resting structures change from inconspicuous white, yellow and green to conspicuous brown and black (Fig. S1b). Each resting structure contains a single ascus, in which usually eight ascospores develop during successful maturation (Fig. S1c). Maturation takes place from late autumn to spring. During spring, the resting structures burst open and the ascospores can infect living plant material. Dormancy of resting structures for more than a single season, as equivalent to seed banks for plants, has not been reported and is regarded as unlikely for powdery mildews (Spencer, 1978; Bélanger et al., 2002). A recent study has revealed that resting structures can be produced through haploid selfing in P. plantaginis, in contrast to the heterothallic nature of the majority of powdery mildews (Tollenaere & Laine, 2013).
Affiliation: Metapopulation Research Group, Department of Biosciences, University of Helsinki, PO Box 65 (Viikinkaari 1), FI-00014, Helsinki, Finland.