The Uneven Distribution of Mating Type Genes in Natural and Cultivated Truffle Orchards Contributes to the Fructification of Tuber indicum

Frequency of the two mating types in the soil under productive and non-productive trees in five French orchards of the Périgord black truffle (Tuber melanosporum Vittad.)

The Périgord black truffle (Tuber melanosporum Vittad.) is an ectomycorrhizal fungus forming edible fructifications. The production of T. melanosporum relies mainly on man-made plantations. T. melanosporum is a heterothallic species requiring the meeting of two partners of opposite mating types to fruit. It is common to have productive and non-productive trees in the same orchard. The aim of our study was to assess the distribution of T. melanosporum mating types in soil under productive and non-productive trees to test whether the presence or absence of one or two mating types could be an indicator of productivity. To achieve this aim, five orchards were selected in various French regions. Soils were harvested under productive and non-productive Quercus pubescens; soil characteristics and the distribution of the mating types in the soil were investigated. No significant differences between productive and non-productive soils according to soil parameters were detected. The total content of T. melanosporum DNA in the soil was significantly higher under productive trees compared with non-productive trees, and it was positively correlated only with soil available phosphorous. Under productive trees, it was more frequent to find both mating types than under non-productive trees. Soils with only one mating type were more frequent under non-productive trees than under productive ones. Moreover, no mating type was detected in the soil of 22% of the non-productive trees. These results suggest that the detection of T. melanosporum mating types in soil could be a tool to optimise the management of truffle orchards (e.g. by spore inoculation).

Effects of truffle inoculation on a nursery culture substrate environment and seedling of Carya illinoinensis

We inoculated Tuber aestivum and Tuber sinoaestivum on Carya illinoinensis to explore the effects of inoculation on host plant growth, enzyme activities, the physicochemical properties of rhizosphere soil, the denitrifying bacterial community in the rhizosphere, and the distribution of mating type genes in the rhizosphere. We found that the Tuber spp. inoculation increased the height of the host plant and that the stem circumference of the host was greater two months after inoculation. Six months after inoculation, the peroxidase activity of the seedlings inoculated with T. sinoaestivum was higher than that of the control. At four and six months after inoculation, the superoxidase dismutase activities of the seedlings inoculated with T. aestivum were higher than those of the seedlings inoculated with T. sinoaestivum. Six months after inoculation, nitrate nitrogen content was lowest in the control and highest in the T. sinoaestivum treatment. Among the nirS-type denitrifying bacteria community, the relative abundances of Proteobacteria were high. T. aestivum and T. sinoaestivum inoculation did not affect the diversity of denitrifying bacteria. The mating type genes MAT1-1-1 and MAT1-2-1 were detected in the rhizosphere of C. illinoinensis inoculated with T. sinoaestivum and T. aestivum, and MAT1-1-1 dominated over MAT1-2-1.