Lack of Linkages among Fruiting Depth, Weight, and Maturity in Irrigated Truffle Fungi Marks the Complexity of Relationships among Morphogenetic Stages

The highly prized black truffle (Tuber melanosporum) has become a model species for ectomycorrhizal fungi biology. However, several questions concerning its reproductive phase remain unanswered. To provide new hypotheses on the fruitbody formation process, we have explored the causal links among development characters of black truffle fruitbodies that are primarily linked to either the mating process, fruitbody growing stage, or maturation. Path analysis was applied to test causal models outlining the relationships among fruitbody development characters such as fruiting depth, weight, shape, and spore maturity. These characters were investigated over a two-season survey and three soil typologies (plus peat-based substrate) under irrigated conditions. We found a clear and generalized relationship between fruitbody weight and shape. Among clusters of fruitbodies we found a positive relationship between the weight of the largest fruitbody and the weight of the remaining fruitbodies. However, no generalized relationships among characters linked to different development stages appeared. Our results were noticeably consistent across soil typologies, both for fruitbodies growing singly and in clusters, indicating that early-developing fruitbody characters did not influence characters linked to subsequent morphogenetic stages. The lack of links among stages opens new perspectives for pre-harvest quality management with stage-specific cultivation practices.

Tuber melanoexcavatum sp. nov., an edible black truffle from China

A new black truffle species with a basal cavity, Tuber melanoexcavatum, is identified and described. The new species is morphologically similar to T. pseudobrumale, T. pseudoexcavatum, and T. mesentericum in having a basal cavity. However, T. melanoexcavatum differs from T. pseudobrumale and T. pseudoexcavatum in having black pyramidal warts and 5 to 8 spored asci, and differs from T. mesentericum by having spiny ascospores and 1 to 5 spored (rarely 6 spored) asci. Phylogenetic analysis indicates that T. melanoexcavatum is most closely related to T. pseudobrumale, but the two still clearly differentiate. Tuber melanoexcavatum grows as a mycorrhizal association with Cyclobalanopsis glaucoides. Tuber melanoexcavatum is considered an edible black truffle species and is indigenous to China.