Federica Piattoni

Techniques for Host Plant Inoculation with Truffles and Other Edible Ectomycorrhizal Mushrooms

Large-scale production of high-quality mycorrhizal plants in the greenhouse is mainstay for the modern cultivation of edible ectomycorrhizal mushrooms (EEMMs). Success at this step not only depends on the reliability of the fungal inoculum used for plantlet mycorrhization but also on the environmental conditions attending symbiosis establishment. Methods developed 40–50 years ago for inoculating host plants with EEMMs are still largely used today, with slight modifications. Mycelial inoculations are used commercially only for some edible ectomycorrhizal (EEM) basidiomycetes, while inoculation with spores is the most common method for producing seedlings colonized with truffle mycorrhizas. However, pure cultures and ectomycorrhizas of Tuber have also been used to obtain mycorrhizal plants mainly for scientific purposes. Mycelium-based inoculum offers many advantages, such as lower contamination risks and more reliable root colonization and provides opportunities for genetic selection of EEMM strains. The long-time preservation of EEM cultures and the creation of germ plasm banks would be an important step to support mycelium-based technologies. To this aim, we demonstrate successful cryopreservation of strains of Tuber borchii and Tuber aestivum. Recent advances in genetics and biotechnology of EEMs and their hosts have the potential to transform the current EEMM nursery trade.

Hypogeous fungi in Mediterranean maquis, arid and semi-arid forests

Hypogeous fungi are common in arid and semi-arid areas of the Mediterranean basin and, in particular, they are found in Italy, Spain, northern African countries (especially in Morocco, Algeria, and Tunisia), and in the Middle East. These fungi and, in particular, some species belonging to the genus Tuber and the desert truffles (Terfezia spp. and Tirmania spp.) form ascomata of considerable economic value. In this review, a panorama of hypogeous fungal diversity and information on their ecology in Mediterranean arid and semi-arid ecosystems have been reported; their economical importance and cultivation potential are also underlined.

First evidence for truffle production from plants inoculated with mycelial pure cultures.

Truffle (Tuber spp.) cultivation is based on raising mycorrhizal trees in greenhouses that have been inoculated with suspensions of ascospores. The problem with this is that pests, pathogens, and other mycorrhizal fungi can contaminate the trees. Furthermore, because ascospores are produced sexually, each plant potentially has a different genetic mycorrhizal makeup from each other so tailoring the mycorrhizal component of plants to suit a particular set of soil and climatic conditions is out of the question. Here, we report on the production of Tuber borchii-mycorrhized plants using pure cultures, establishing a truffière with these and subsequent production of its fruiting bodies. This study opens up the possibility of producing commercial numbers of Tuber-mycorrhized trees for truffle cultivation using mycelial inoculation techniques. It also poses questions about the mechanism of fertilization between the different strains which were located in different parts of the experimental truffière.

Chinese Tuber aestivum sensu lato in Europe

Two specimens of Tuber aestivum sensu lato from China were found between T. aestivum ascomata for sale in Italy. The morphological features of these ascomata were intermediate between those of T. aestivum and Tuber mesentericum. The spores were roundish and smaller than those of T. mesentericum and T. aestivum. Phylogenetic analyses showed that the Chinese specimens are placed in a separate clade to T. aestivum and T. mesentericum. This, together with the supporting morphological differences, strongly suggests that the two Chinese truffles are a separate taxon.

Interrelationships Between Wild Boars ( Sus scrofa ) and Truffles

The European population of wild boars has increased considerably since the 1960s, leading to increased damage to agroecosystems. Their distribution coincides with the natural distribution of the most important commercial Tuber species. In this chapter, the truffle/wild boar interrelationships are discussed and include the importance of truffles in their diet, their role in spore dispersal, and their impact on cultivated truffieres. Wild boars eat a wide variety of foods: plant matter, animals, fungi, bulbs, tubers, and roots. Analyses of their feces and stomach contents suggest they can be considered casual or opportunistic mycophagists, with fungal consumption simply dependent on the availability of other foods. The ingestion of hypogeous fungi is more frequent than that of epigeous mushrooms. Their rooting behavior primarily reduces plant cover and diversity, affects the first 15–70 cm of the litter layer, and can damage up to 80 % of the forest soil surface. Excavation may cause great economic losses to cultivated truffieres, not only in terms of truffle predation but also through soil disturbance so that there can be significant increases in truffle production after fencing cultivated truffieres damaged by wild boars. Because wild boars can move as much as 15 km in a day, they efficiently contribute to long-distance dispersal of truffle spores. Moreover, the action of the degradation of the digestive enzymes on asci and spore wall improves germination and the ability to form ectomycorrhizas and results in wild boars playing a pivotal role in truffle colonization of new habitats.

Studies on the potential role of root exudates in the interaction between musk melon roots and Fusarium oxysporum f. sp. melonis

The interactions of resistant (Bingo, Giusto, Sweetness) and susceptible (Cantalupo di Charantais, Harper, Retato degli Ortolani) muskmelon cultivars with Fusarium oxysporum f. sp. melonis races 0, 1, 2 (FOM0, FOM1, FOM2) were studied through the effects of root exudates (REs), released by 14 and 21 days old hydroponic plantlets, on the percentage of germinated conidia. REs caused a moderate promotion or inhibition of conidial germination or did not cause any effect. The observed patterns mostly depended on pathogen race, plant cultivar and plant age: among the races, only FOM2 conidial germination was reduced by almost all REs but never totally; among the cultivars, none affected FOM0 conidial germination at any plant age. FOM1 conidial germination was either not affected or enhanced, depending on plant age. REs from Bingo and Retato degli Ortolani were also tested for their effects on FOM2 hyphal growth, number and length of germ hyphae and for root callose deposition after FOM2 challenge. Inhibitory effects of REs on the formation of germ hyphae by conidia of FOM2 were not noted. In case of the macroconidia the number increased. The length of germ hyphae was increased in both macro and microconidia and more pronounced with REs from cultivar Bingo. REs from Bingo and Retato degli Ortolani enhanced hyphal growth of FOM2. Fluorescence microscopy showed that FOM2 infection of roots caused callose deposition in root cortical cells in the resistant cultivar Bingo, but not in the susceptible Retato degli Ortolani. In conclusion, under our experimental conditions, REs appeared to be only partially involved in plant-pathogen interaction, whereas callose deposition in the roots of the resistant cultivar Bingo was elicited after inoculation with FOM2.