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To study the dispersal process of the pine sawyer Monochamus alternatus (Hope) in frontier populations, a microsatellite marker-based genetic analysis was performed on expanding populations at the northern limit of its range in Japan. In Asian countries, M. alternatus is the main vector of pine wilt disease, the most serious forest disease in Japan. Sawyers were collected from nine sites near the frontier of the pine wilt disease damage area. A mountain range divides the population into western and eastern sides. Five microsatellite loci were examined and a total of 188 individuals was genotyped from each locus with the number of alleles ranged from two to nine. The mean observed heterozygosity for all loci varied from 0.282 to 0.480 in the nine sites, with an overall mean of 0.364. None of the populations have experienced a significant bottleneck. Significant differentiation was found across the mountain range, but the genetic composition was similar amongst populations of each side. It is believed that the mountain range acts as a geographical barrier to dispersal and that gene flow without a geographical barrier is high. On the west side of the mountain range, a pattern of isolation by distance was detected. This was likely to be caused by secondary contact of different colonizing routes on a small spatial scale. Based on these data, a process linking genetic structure at local (kilometres) and regional spatial scales (hundreds of kilometres) was proposed.

Summary The distribution of genets of a root and butt rot pathogen Heterobasidion parviporum was studied in a 68-year-old Abies sachalinensis plantation in Japan. A total of 33 pure cultures of H. parviporum were isolated from diseased Todo fir stumps after clear-felling. Individual genets of the fungus were identified by three different methods: somatic incompatibility test, random amplified polymorphic DNA, and DNA microsatellite analyses. The combined results of the three analyses identified at least eight genets within a 60 × 100 m plot. One genet, consisting of only one isolate, was genetically differentiated from the other genets by all three methods; the other 32 isolates, however, were grouped with minor discrepancies, into seven genetically close genets. The genetic differentiation was lower than that recorded previously in Europe. A single genet infected 1-15 trees in the plot. The longest distance of the two most isolated trees of a single genet was 51 m. The close genetic relationship between genets and their large sizes suggest that basidiospores from restricted sources (just a few fruiting bodies) infected the site before establishment of the present Todo fir stand and that the disease has spread mainly by vegetative growth of the mycelia through root contact. Absence of fruiting bodies of the fungus in the study plot also suggests the greater importance of vegetative growth than spore dispersal for the spread of this fungus. [ABSTRACT FROM AUTHOR]