Ectomycorrhizae and ectomycorrhizal fungal fruit bodies in pine stands differentially damaged by pine wilt disease

Abstract

affected not only by abiotic environmental factors such as desiccation stress (Suzuki and Kiyohara 1978), but also by biotic factors such as ectomycorrhizal association (Kikuchi et al. 1991).Ectomycorrhizae are a symbiotic association in which the host tree is associated with fungi. The host tree provides carbohydrates to the fungi via ectomycorrhizae, and, inversely, the fungi enhance host tree absorption of soil minerals and water (Finlay and Read 1986), improve host resistance to root disease (Marx 1969;Buscot et al. 1992), and ameliorate soil desiccation stress (Mexal and Reid 1973).Regarding the relationship between ectomycorrhizal abundance and pine wilt damage, Akema and Futai (2005) found that pine wilt damage was lighter and the rate of ectomycorrhizal root tips was higher on upper slopes than lower slopes. Thus, ectomycorrhizal abundance is thought to be related to pine wilt damage, but the causal association is not clear. Kikuchi et al. (1991) reported that mortality caused by inoculation by the pathogenic nematode was lower in P. densifl ora seedlings with ectomycorrhizae than without ectomycorrhizae. After inoculation of pathogenic nematodes on P. thunbergii seedlings, ectomycorrhizae did not disappear; however, ectomycorrhizal development ceased (Ichihara et al. 2001). To clarify this relationship, more fi eld observations and experiments are needed.Previous studies have not considered two potentially important factors: soil conditions and the ectomycorrhizal community structure. Akema and Futai (2005) reported a difference in soil moisture between the upper and lower slopes. Soil conditions such as soil moisture can infl uence ectomycorrhizal association (Slankis 1974). Thus, the effects of soil conditions should be considered to understand the relationship between ectomycorrhizal association and pine wilt damage. Neither Akema and Futai (2005) nor Ichihara et al. ( 2001) reported the ectomycorrhizal community structure on pine roots. Kikuchi et al. (1991) compared the different effects of ectomycorrhizal species on pine resistance, but they observed only two fungal species. The symbiotic function of ectomycorrhizae differs among fungal species (Nara 2006). Thus, not only the amount of ectomycorrhizae,