Keisuke Obase

Mycorrhizal associations in woody plant species at the Mt. Usu volcano, Japan

We investigated the association between ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi and pioneer woody plant species in areas devastated by the eruption of Mt. Usu, Japan, in 2000. We observed eight woody plant species at the research site, most of which were associated with ECM and/or AM fungi. In particular, dominant woody plant species Populusmaximowiczii, Salixhultenii var. angustifolia and Salixsachalinensis were consistently associated with ECM fungi and erratically associated with AM fungi. We found one to six morphotypes in the roots of each ECM host and, on average, two in the roots of each seedling, indicating low ECM fungal diversity. ECM colonization ranged from 17 to 42% of root tips. Using morphotyping and molecular analyses, 15 ECM fungi were identified. ECM fungi differed greatly between hosts. However, Laccaria amethystea, Hebelomamesophaeum, Thelephoraterrestris and other Thelephoraceae had high relative colonization, constituting the majority of the ECM colonization in the roots of each plant species. These ECM fungi may be important for the establishment of pioneer woody plant species and further revegetation at Mt. Usu volcano.

Mycorrhizal colonization status of plant species established in an exposed area following the 2000 eruption of Mt. Usu, Hokkaido, Japan

We investigated the ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) colonization status of plant seedlings that established in areas devastated by the eruption in March 2000 of Mt. Usu, Hokkaido, Japan. In 2005, we estimated the mycorrhizal colonization ratios and frequencies in seedlings of twelve herbaceous and seven woody plant species. Although arbuscular mycorrhizas were found to colonize Equisetum arvense and Polygonum sachalinense, they were presented at very low frequencies and colonization ratios. Other herbaceous plants exhibited higher frequencies of AM associations and either AM and/or ECM fungal associations were observed in all of the woody plant seedlings investigated. The dominant woody plant species (Populus maximowiczii, Salix sachalinensis and Salix hultenii var. angustifolia) associated mainly with ECM fungi and exhibited variable associations with AM fungi. Mycorrhizal associations were common and significant events for plant establishment, even in the early stages of the revegetation process.

Progress and Challenges in Understanding the Biology, Diversity, and Biogeography of Cenococcum geophilum

Cenococcum geophilum (Dothideomycetes, Ascomycota) is one of the most common ectomycorrhizal fungi in boreal and temperate regions. Although C. geophilum was originally considered as a single species, accumulating evidence suggests that C. geophilum is actually a diverse species complex. Here we provide an overview of the current data on global host range, distribution and biogeography of C. geophilum and discuss what is known about the spatial genetic structure at scales from soil cores to biomes to continents. Recent molecular data indicate that the genetic diversity within C. geophilum can be incredibly high, even at the scale of a single soil core. This highlights the need to characterize Cenococcum samples phylogenetically prior to population studies so that cryptic, reproductively isolated species are not admixed together in the analyses. Also sampling design and effort are critical for understanding population and phylogenetic diversity of C. geophilum. A recent population study targeted one Cenococcum lineage in Japanese pine forests and found no spatial autocorrelation at the forest stand level but did find evidence for a pattern of isolation by distance at larger spatial scales. These observations are consistent with the possibility of cryptic recombination. Another recent phylogenetic study found that several Cenococcum lineages are widely distributed across multiple regions and continents. This indicates that some lineages within C. geophilum may be ancient or that cryptic long-distance dispersal is ongoing. Overall, our assessment and review of the recent literature suggests that additional research is needed to understand the population structure and biology of C. geophilum.

Ectomycorrhizae formed by three Japanese truffle species (Tuber japonicum, T. longispinosum, and T. himalayense) on indigenous oak and pine species

Modern truffle cultivation systems started in Europe in the early 1970s and are now successfully used for several European truffles throughout the world. However, systems for indigenous novel truffle species need to be developed in several regions, especially where truffle cultivation has not been attempted so far, such as in Japan. Recently, two new and one known truffle species that are expected to be edible were reported from Japan: Tuber japonicum, T. longispinosum, and T. himalayense. Here, we conducted mycorrhization trials between these three truffle species and four native tree species in Japan (Quercus acutissima, Q. phillyraeoides, Q. serrata, and Pinus densiflora) using spore suspension and trap-plant seedling techniques under axenic pot culture conditions to understand their potential host ranges and mycorrhizal morphologies and to determine whether these inoculation methods are applicable for mycorrhization of Japanese truffles with native host plants. Of the 12 combinations, nine were successful for mycorrhization, including both oak and pine trees. The T. japonicum mycorrhiza was characterized by short, needle-shaped cystidia without septa, whereas the two black truffles, T. longispinosum and T. himalayense, were indistinguishable from each other because they shared the same morphological and anatomical characters such as brownish, long cystidia with right angle ramification. These features were similar to related black truffle species. The results of the present study indicate that the inoculation method used for European truffles can also be applied for mycorrhization between Japanese truffle species and compatible native pine and/or oak hosts in Japan.

Inocybe nitidiuscula, new to Japan

A species of the genus Inocybe, which has not been recorded previously in Japan, is described and illustrated as a new record. Inocybe nitidiuscula (Britzelm.) Sacc. belongs to the subgenus Inocibium (Earle) Singer.