Abstract: In truffle beds planted in environments not suitable for the truffle species chosen , mychorrhizal substitution usually takes place after a period of time . The present work was aimed at verifying the capacity of mycorrhization of Tuber borchii Vittad . in the presence of other Tuber species in the soil . Some young plants of Quercus pubescens Willd . were inoculated in the same conditions using two different substrates (natural and artificial substrate ) and different species of Tuber as inoculum. In fall 2004 , spring 2005 and in spring 2006 , the percentage of mycorrhization for each of the species of fungi involved was assessed in 32% of the plants in each inoculation test . The most abundant mycorrhizae of T. borchii were detected in roots of plants grown in natural soil . But T. brumale Vittad . shows remarkable percentages of mycorrhization ( up to 50%) and seems to substitute T. borchii in some cases . The results indicate that truffle beds of T. melanosporum Vittad . and
T. aestivum Vittad . planted in soils containing propagation elements of T. borchii do not give the desired production .

Key words: Mycorrhization