Persistence of some Australian Pisolithus species introduced into eucalypt plantations in China

Abstract

Some eucalypt plantations in south China grow poorly because of soil infertility and low diversity of compatible ectomycorrhizal fungi. One option to improve productivity of plantations is to introduce beneficial fungi. In order to evaluate persistence of introduced symbiotic fungi, there is a need to discriminate them from any indigenous related species. Eucalypt mycorrhizal trial sites, established for nutrition and survival studies, were used for this purpose. Seedlings of Eucalyptus camaldulensis and Eucalyptus urophylla had been inoculated with pure cultures of selected Australian ectomycorrhizal fungi, including three isolates of Pisolithus albus and one isolate each of two unnamed Pisolithus spp., and ectomycorrhizal seedlings had been out-planted at two sites in Guangzhou Province, People’s Republic of China. Sequences of the internal transcribed spacers (ITSs) of ribosomal DNA (rDNA) from inoculant fungi and fungi re-isolated from sporocarps in the field were compared. Sequencing confirmed that an Australian isolate (H4111) of one unnamed Pisolithus spp. had persisted in competition with an indigenous Pisolithus spp. Selected isolates of Australian Pisolithus formed macro- and micro-morphologically typical ectomycorrhizas in pure culture syntheses and in the field. In comparison, the indigenous Chinese Pisolithus formed an incomplete association with a poorly developed mantle. Comparisons between ITS sequences from Pisolithus isolates associated with Eucalyptus spp. from elsewhere in the world and ITS sequences of Australian Pisolithus spp. indicate that the same unnamed Pisolithus spp. has also become established in Portugal, Brazil and South Africa. Because Pisolithus isolate H4111 produced sporocarps in south China under eucalypts and promoted tree growth, this fungus would be useful in spore orchards to provide spore inoculum for eucalypt nurseries. The local Chinese Pisolithus is not recommended for inoculation programs because it is ineffective in forming mycorrhizas with eucalypts. The isolate H4111 is from a Pisolithus that occurs naturally along the east coast of Australia. Although this Pisolithus has been widely dispersed with eucalypts in other parts of the world, it is not present in eucalypt plantations in east Asia.