The fungus Tricholoma matsutake forms an ectomycorrhizal relationship with pine trees. Its sporocarps often develop in a circle, which is commonly known as a fairy ring. The fungus produces a solid, compact, white aggregate of mycelia and mycorrhizae beneath the fairy ring, which in Japanese is called a 'shiro'. In the present study, we used soil dilution plating and molecular techniques to analyze the bacterial communities within, beneath, and outside the T. matsutake fairy ring. Soil dilution plating confirmed previous reports that bacteria and actinomycetes are seldom present in the soil of the active mycorrhizal zone of the T. matsutake shiro. In addition, the results showed that the absence of bacteria was strongly correlated with the presence of T. matsutake mycorrhizae. The results demonstrate that bacteria, especially aerobic and heterotrophic forms, and actinomycetes, are strongly inhibited by T. matsutake. Indeed, neither bacteria nor actinomycetes were detected in 11.3% of 213 soil samples from the entire shiro area by culture-dependent methods. However, molecular techniques demonstrated that some bacteria, such as individual genera of Sphingomonas and Acidobacterium, were present in the active mycorrhizal zone, even though they were not detected in soil assays using the dilution plating technique.

BackgroundThe ambrosia beetle, Platypus quercivorus, is the vector of oak wilt, one of the most serious forest diseases in Japan. Population genetics approaches have made great progress toward studying the population dynamics of pests, especially for estimating dispersal. Knowledge of the genetic structuring of the beetle populations should reveal their population history. Using five highly polymorphic microsatellite loci, 605 individuals from 14 sampling sites were assessed to infer the ongoing gene flow among populations as well as the processes of expansion of damaged areas.ResultsPopulation differentiation (FST = 0.047, G'ST = 0.167) was moderate and two major clusters were detected by several methods, dividing the samples into north-eastern and south-western populations, a similar genetic divergence was reported in host oak trees. Within the north-eastern populations, the subgroups mostly corresponded to differences in the collection period. The genetic characteristics of the population might have changed after 2 years due to the mixing of individuals between populations with enhanced migration related to population outbreaks. Because isolation by distance was detected for whole populations and also within the north-eastern populations, migration was considered to be limited between neighbouring populations, and most populations were suggested to be in genetic equilibrium of genetic drift and gene flow. Recent bottlenecks were found in some populations with no geographical bias; however, they were all from newly emerged oak wilt forests. The emergence of oak wilt should have induced intense fluctuations in the beetle population size.ConclusionsBecause the genetic boundaries coincide, we suggest that the geographical structuring of the beetle was formed by co-evolution with the host species. Our findings indicate the oak wilt expansion process.

Abstract:To demonstrate influence of water content of host tees on attacking behavior of Platypus quercivorus and on symbiotic fungi (yeasts and Raffaelea quercivora), the number of beetles landing on bait logs with their water content artificially changed and the number of entry holes bored by the beetles into the bait logs were counted, and the ratio of galleries with eggs or larvae and the ratio of wood pieces with the symbiotic fungi were investigated. A multiple regression analysis of the number of beetles captured and the number of entry holes bored by the beetles was performed with the length and water content of bait logs as explanatory variables. The result suggest that males land on bait logs by judging the length of bait logs or something related to their length, and that males bore into bait logs by judging both the length of the bait logs and water content of the bait logs at the time of breeding or by judging something related to both these factors. At a part with the low water content at the time of breeding, the number of entry holes per m 2 , the ratio of galleries with eggs or larvae, and the ratio of wood pieces containing symbiotic fungi were low, suggesting that P. quercivorus fails to reproduce in a part with low water content, because symbiotic fungi fail to propagate in this part. From the above, it is hypothesized that male P. quercivorus chooses host trees with large breeding capacity by a certain method, resulting in them tending to choose host trees where the symbiotic fungi grows easily because the water content is maintained for a long time.

Myctolaimus platypi sp. n. is described and figured. The third-stage dauer juveniles of M. platypi sp. n. were isolated from the underside of the elytra of the oak borer, Platypus quercivorus, and were reared on an Asparagine-Mannitol (A-M) agar. Specimens of adult nematodes for description and measurements were collected from a 2-week-old culture on A-M agar. The new species is characterised by having the stoma shorter than the pro-metacorpus, shape of the rounded-cylindroid pro-metacorpus, the obvious longitudinal striations on the cuticle, and thick cuticle. The male and female of the new species have a body length of ca 700-1000 µm, a value of ca 20, b value of ca 6, and c value of ca 10. Males of the new species have strongly arcuate, C-shaped spicules 71 (62-80) µm long, 29 (25-35) µm long gubernaculum with pointed distal end, and nine pairs of caudal papillae. There is no bursa. Ceratosolenus is proposed as a junior synonym of Myctolaimus and the following new combinations are also proposed: M. anoplophorae comb. n.; M. inevectus comb. n.; and M. racemosa comb. n.

The effects of the incubation period upon the antigenicity of trichophytin were studied. Trichophytin antigens were prepared from a culture filtrate of Trichophyton mentagrophytes var. mentagrophytes incubated in Sabouraud's broth for 1, 3, 5, 7, 9, 11 weeks, 6 and 12 months. With those antigens precipitin tests were performed in sera of experimental Trichophyton mentagrophytes var. mentagrophytes infected rabbits. The trichophytin antigens derived from 9 and 11 week-culture media were found to be highly reactive.