1 Introduction

Cultivation of Edible Ectomycorrhizal Fungiby in Vitro Mycorrhizal Synthesis 255
2.1
Sporal Inoculum
Spores are the preferred inoculum for the colonization of forest tree transplants
with Pisolithus tinctorius, Rhizopogon luteolus and Rhizopogon vinicolor
(Garbaye 1991). This method has also been the mainstay for producing
Tuber spp. colonized plants for the past 30 years in Italy, France
and New Zealand (Fontana 1967; Chevalier et al. 1973; Mannozzi Torini
1976; Bencivenga 1982; Tibiletti and Zambonelli 1999; Chevalier 2001; Hall
et al. 2003b). However, those details of this method ensuring success, such
as the amount and treatment of sporal inoculum, potting mix and greenhouse
conditions remain trade secrets (Hall et al. 2003b). This inoculation
method can be applied to most of the prized Tuber species, such
as T. melanosporum, T. aestivum and T. borchii,butnottoT. magnatum
because of difficulties with the germination of its spores (Gregori 2002).
Although sporal inocula have also been used for T. matsutake and some
other edible ectomycorrhizal mushrooms, they have not proved successful.
Sporal inoculation techniques are unlikely to be used for mycorrhizal synthesis
in vitro because the inoculum invariably contains other fungi and
bacteria which may inhibit the development of the ectomycorrhizal fungal
mycelia in vitro (Bedini et al. 1999; Barbieri et al. 2004, unpubl. data).
2.2
Mother-Plant Technique
This inoculation technique exploits the mycelium’s capacity to propagate
from an already colonized root to another root, thus spreading the mycorrhizal
colonization. A mother plant, already colonized, is planted in the
middle of a large container and then surrounded by other plantlets, obtained
by seed germination, scion or in vitro micropropagation (Zuccherelli
1990). Alternatively, parts of the mycorrhized roots of the mother plant are
collected and placed in contact with the roots of sterile plants (Chevalier
and Grente 1973). This method is widely used for the production of plants
colonized with Tuber spp.
This technique is cheaper than the sporal inoculation method since
fruiting bodies do not need to be purchased. Moreover, it has been used
extensively in the production of T. magnatum colonized plants, which
are difficult to obtain using the sporal inoculation method. However, this
method carries a high risk of spreading contaminating and possibly very
competitive ectomycorrhizal fungi. Even though growers usually control
the mother plants or the root sections to be used as inocula, some contaminated
roots may escape detection. Indeed, some contaminating fungi,