How many samples do you need to assess mycorrhization in Tuber melanosporum orchards? A methodology for a reliable estimation

The cultivation of Tuber melanosporum Vittad., the black truffle, recently expanded all over the world. For successful truffle production, an important factor to consider is the mycorrhization level of the planted mycorrhized-seedlings. To assess the mycorrhization level of a truffle orchard it is necessary to develop a sampling strategy. Root sampling is time-consuming and a delicate operation because it is easy to disturb the ectomycorrhizal communities of the truffle-plants. A standardized and reproducible methodology for sampling mycorrhized roots in truffle orchards has not yet been developed. Consequently, we sampled five T. melanosporum truffle orchards located in Central Italy to determine: (1) the relationship between the number of sampled plants and the presence of T. melanosporum and other ectomycorrhizal Fungi; (2) the minimum number of trees (MNT) needed to achieve a reliable mycorrhization estimate and the minimum sampling ratio (MSR) as the percentage of MNT over the total number of trees present in the truffle orchard. Using a general linear model, we calculated MNT for T. melanosporum and other Fungi in two sampling campaigns in each truffle orchard. The mean values of the MNT ranged among 12–17 and 17–18, respectively, for T. melanosporum and for other Fungi. According to our findings we suggest that at least a MSR of 12% should be considered to have a fair estimate of the mycorrhization level of a truffle plantation.