Genotypic diversity of the Asiatic black truffle, Tuber himalayense , collected in spontaneous and highly productive truffle grounds

Tuber himalayense is a species of edible Asiatic black truffle which is sister to Tuber indicum. Local populations contribute significantly to the reproduction of truffles, but fundamental data of fine-scale genetic structure is lacking in Asiatic truffle species. In this study, we provide the first report on the genotypic diversity and spatial fruiting pattern of an Asiatic truffle T. himalayense, in two spontaneous productive truffle grounds 140 m apart from one another in Yamanashi, Japan. Ascocarps were collected from 2004 to 2009 and in 2011. The spatial distribution of samples was recorded and genotypic diversity of the fungal individuals was examined using 15 newly developed and 4 existing simple sequence repeat (SSR) markers. The spatial distribution analyses suggested non-random, year-specific aggregation patterns of ascocarps in both plots. However, no consistent tendency was observed across the entire sampling period, with fruiting positions showing neither an obvious expansion nor a steady displacement. Although only a single SSR genotype, representing one gleba-forming maternal individual, was detected, the genotype was further divided into two different mating types, suggesting multiple, closely related individuals that were indistinguishable using the SSR analysis. The results indicated strong founding effects along with high inbreeding within populations, likely due to the limited dispersal opportunities into these sites. Despite low genetic diversity in the truffle grounds, the plots remained productive over the sampling years, indicating that low genetic diversity does not necessarily have an adverse effect on truffle production, at least not during a period of several years.