Aflatoxins are carcinogenic mycotoxins formed by a number of fungi in the genus Aspergillus. The major fungi responsible for aflatoxin formation in crop seeds in the field and in storage are Aspergillus flavus and A. parasiticus. This review emphasizes developmental, environmental, biological, and chemical factors that influence aflatoxin formation by A. flavus and A. parasiticus.

Based on the result of morphological and the phylogenetic analyses, three Bionectria (Bionectriaceae: Hypocreales) species are added to the mycobiota of Japan. Among them, one found in Okinawa and Kagoshima Prefectures is described as a new species, Bionectria pseudostriatopsis (anamorph: Clonostachys pseudostriatopsis). The other two, B. grammicospora and B. sporodochialis, are new records from Japan. Additional distribution records are given for Bionectria species hitherto known in Japan.

Five new species of the Boletaceae (Agaricales) from Japan are described and illustrated: (1) Boletus bannaensis sp. nov. (section Luridi), forming a grayish-brown pileus and rufescent flesh, found in subtropical evergreen broad-leaved forests; (2) Leccinum rhodoporosum sp. nov., forming discolorous red pores, a whitish stipe covered overall with violet-brown to blackish-brown furfuraceous scales and fusoid-cylindrical brown basidiospores, found in subtropical evergreen broad-leaved forests or warm-temperate Quercus-Pinus forests; (3) Pulveroboletus brunneoscabrosus sp. nov., forming a lemon-yellow pulverulent basidiomata covered overall with orange to brownish-orange appressed scales, found in subtropical to warm temperate evergreen broad-leaved forests; (4) Rubinoboletus monstrosus sp. nov., forming a brownish-orange to yellowish-brown pileus and a very short, nonreticulate, hollow stipe, found in subtropical evergreen broad-leaved forests; and (5) Tylopilus fuligineoviolaceus sp. nov., having a deep violet to blackish-brown pileus and brunnescent hymenophore, found in warm temperate Quercus-Castanopsis forests.

Two species of Leptographium were isolated from blue-stained sapwood of Pinus khasya and bark beetle galleries in pine trees near Chiang Mai, Thailand. Based on morphological observations, these two species were identified as L. pini-densiflorae and L. yunnanense. This is the first record of these fungi in Thailand. Leptographium yunnanense appeared to be associated with Polygraphus major.

Three edible mycorrhizal mushrooms, Tricholoma portentosum, T. saponaceum, and T. terreum, that had formed ectomycorrhizas with Pinus densiflora seedlings in vitro, were maintained in open pot culture for 3 years under laboratory conditions. Tricholoma portentosum and T. saponaceum produced fruit bodies several times. For T. terreum, which produced a single fruit body in the third year, this is the first report of mushroom production under controlled conditions. Morphological observation of fruit bodies indicated that they were mature, i.e., well-organized cap, stem, and gills, and basidiospores. These results suggest that cultivation of these three edible Tricholoma mushrooms is feasible.

We isolated and characterized the genomic and complementary DNAs encoding a chitin synthase from an edible basidiomycetous mushroom, Lentinula edodes. The gene (which we designated Lechs1) contains a large open reading frame encoding a polypeptide of 1937 amino acid residues. The open reading frame is interrupted by 14 small introns (49–116 bp). The gene product (LeChs1) consists of a myosin motor-like domain in its N-terminal half and a chitin synthase domain in its C-terminal half, analogous to the class V and VI chitin synthases of other filamentous fungi. Phylogenetic analysis demonstrated that LeChs1 is classified into class VI chitin synthases. Southern blot analysis indicated that Lechs1 is a single-copy gene per haploid genome and that L. edodes has no other highly homologous chitin synthase genes. Northern blot analysis revealed that Lechs1 is expressed throughout the whole stages of fruitbody formation of L. edodes, but its expression level gradually declines in a fruit body-maturation-dependent manner with highest expression in vegetative mycelia and fruit body at the early stage of maturation (immature fruit body). This is the first report on the isolation and characterization of the gene encoding a chitin synthase with a myosin motorlike domain from basidiomycetes.

To obtain a homothallic mutant in Lentinula edodes, basidiospores derived from the common Bmut dikaryon (A1B1mut × A2B1mut) were treated with UV irradiation. Of a total of approximately 5000 monosporous cultures recovered, a single basidiospore isolate was found to produce the hyphae bearing clamp connections without mating. This mutant strain could form fruit bodies, and all its single basidiospore isolates developed into colonies with clamp connections. Such homothallic behaviors were transmitted from the mutant strain to the next generation. During the germination and following hyphal elongation in a single basidiospore of mutant strain, clamp connections were clearly detected in multicellular hyphae, which contained two nuclei in each cell. Their clamp connections were morphologically variable, viz., pseudo, abnormal, and true clamps. Amplified fragment length polymorphism (AFLP) profiles among the basidiospore isolates of mutant strain were identical, indicating that the mutant strain produced isogenic basidiospore progeny.

Cortinarius breviradicatus sp. nov., found in deciduous forests, is described and illustrated from Niigata, Japan. It is characterized by its medium-sized to large dark brown basidiocarp, acutely conical pileus, and rooting stipe, and by subglobose to broadly ellipsoid basidiospores. In addition, the extracting solution from its basidiocarps exhibits a strong fluorescence around 400–430 nm in ultraviolet radiation (250 nm), which was observed in a species of Cortinarius sect. Orellani. The new species belongs to the section Orellani. The differences between the new taxon and similar species are briefly discussed.

A genomic DNA sequence and cDNA encoding a putative manganese peroxidase were isolated from the white-rot basidiomycete Lentinula edodes. The gene, called lemnp1, consists of a 1985-bp open reading frame interrupted by 16 introns and was flanked by an upstream region having putative CAAT, TATA, and heat shock elements and by a downstream region having polyadenylation signals. The lemnp1 gene encodes a protein of 364 amino acids that shows high sequence homology to manganese peroxidases of other basidiomycetes. The deduced N-terminal amino acid sequence is different from the L. edodes manganese peroxidase reported previously.

Tricholoma fulvocastaneum is recorded from Thailand for the first time. This edible ectomycorrhizal fungus is associated with Castanopsis tribuloides (Fagaceae) in mixed evergreen forest in northern Thailand. Conventional and molecular methods were carried out to confirm its identity.