Specialization of a fungal pathogen on host tree species in a cross‐inoculation experiment

Abstract

1. In forest communities, the Janzen-Connell (J-C) model proposes that species diversity is maintained by noncompetitive distance-or density-dependent seedling mortality caused by host-specific natural enemies. Host specificity, however, has not been fully elucidated. 2. We conducted a cross-inoculation experiment to evaluate the host specificity of a pathogenic fungus, Colletotrichum anthrisci. The fungus was isolated from seedlings of four tree species (Prunus grayana, Fraxinus lanuginosa, Cornus controversa and Magnolia obovata), all of which were killed by damping-off disease beneath conspecific adults. Each fungal isolate was then inoculated into seedlings of P. grayana and F. lanuginosa. Molecular identification [internal transcribed spacer (ITS) sequences] also confirmed that all isolates (strains) showed 99-100% similarity with C. anthrisci, irrespective of their origin. 3. In both P. grayana and F. lanuginosa seedlings, all isolates of the pathogen caused damage, irrespective of origin, but the damage was more severe with the isolate from conspecifics rather than from any of the three heterospecifics. 4. In response to infection, callose papillae were deposited on the inner side of the leaf cell wall of seedlings in P. grayana; then, circular abscission layers formed between two layers of leaf cells surrounding the locus of infection. The central area of the infection was completely cut off from the rest of the leaf. In F. lanuginosa, infected leaves of seedlings were shed immediately after inoculation. This defensive behaviour, which may prevent further pathogen invasion, was more frequent in seedlings inoculated with isolates from conspecifics than from heterospecifics in both species. 5. Synthesis. Although the pathogenic fungus C. anthrisci is ubiquitous and attacks a wide range of host species, virulence was much stronger for strains derived from conspecifics rather than from heterospecifics, suggesting local adaptation and development of host specificity. If host specificity is common for several pathogens within a microbial community in a given area occupied by an adult, and the trait is also common for multiple tree species co-occurring within a forest community, the J-C model would be applicable to explain tree species diversity.

Evolution of host range inColeosporium ipomoeae, a plant pathogen with multiple hosts

“…With very few exceptions (11,12), the evolution of pathogen host range has been examined, both theoretically and empirically, for a single pathogen species interacting with a single host species. Many pathogens, however, are capable of infecting multiple host species.…”

Roles of thinning intensity in hardwood recruitment and diversity in a conifer, Criptomeria japonica plantation: A 5-year demographic study

“…Furthermore, compared to abiotic factors, biotic interactions facilitate the coexistence of tree species at much smaller scales within forest communities (e.g. Packer and Clay, 2000;Seiwa et al, 2008;Konno et al, 2011). An increasing body of evidence strongly suggests that the recovery of diversity via a fine-scale mixture of species is necessary for forest managers to more sustainably maintain forest production and to effectively increase ecosystem services.…”

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“…Bell, Freckleton & Lewis ; Bagchi, Press & Scholes ; Bagchi et al . ; Gallery, Moore & Dalling ; Lewis ; Konno, Iwamoto & Seiwa ; Mordecai ; Liu et al . ,b; Fricke, Tewksbury & Rogers ; Gripenberg et al .…”