Edaphic and temporal patterns of Tuber melanosporum fruitbody traits and effect of localised peat-based amendment

Abstract

Tuber melanosporum cultivation, fruitbody traits are gaining relevance due to their increasing prominence on prices. We investigated the edaphic and temporal patterns of fruitbody traits and characterised the effect of truffle nests (localised peat-based amendment supplemented with T. melanosporum spores) on traits. We monitored fruitbody traits throughout two fruiting seasons in three blocks along a soil gradient. Each trait followed specific edaphic and temporal patterns. The number of fruitbodies per dig and spore maturity followed characteristic within-season trends, whereas fruitbody weight and infestation by truffle beetles were subject to complex interactions among edaphic and temporal variables, suggesting a relevant influence of annual environmental conditions. The application of truffle nests increased fruitbody depth, improved its shape and decreased infestation by truffle beetles. Nests increased the number of fruitbodies per dig, but only in two of the soils, suggesting a relevant role of the bulk soil/substrate interface in fruiting initiation. These results outline a complex scenario, with each trait being differently affected by environmental factors. In this scenario, nests proved to effectively modify several traits, although not always in the desired direction. The European black truffle (Tuber melanosporum) is an ectomycorrhizal fungus highly appreciated in "haute cuisine" due to its organoleptic properties. It grows wild in open oak forests of southern Europe, although nowadays most T. melanosporum production is harvested in orchards planted with seedlings previously inoculated in controlled conditions. Truffle cultivation has advanced greatly in recent decades and has expanded worldwide 1. This is leading to an increased and more stable supply of truffles to markets in recent years, thus encouraging price differentiation by quality 2. Commercial quality standards are defined by both pre-harvest fruitbody (FB) traits and post-harvest practices 3. The most important among the former are FB ripeness, gleba colour (associated to spore maturity), abiotic and biotic damages, fresh weight and shape 4. Despite recent advances, truffle cultivation is not completely domesticated yet, as the uncertainties around the mating process and the FB formation process remain 5,6. The environmental mechanisms triggering fruiting and influencing FB development and maturation are still poorly understood 6,7. Edaphic and climatic factors have a key role in ectomycorrhizal FB yields, phenology and morphology 8-10. This is particularly likely to apply to truffles, which grow below ground and require several months to develop and ripen 11,12. Information on the influence of environmental factors on FB traits could help to clarify the ecology of T. melanosporum and could be useful for improving productivity and sustainability in truffle cultivation. Unraveling the linkages between FB traits and edaphoclimatic conditions is difficult because: (1) the long period of formation of truffle FBs hinders the identification of ...

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

“…The study was conducted in a 15-ha truffle orchard established in 2001 with Quercus ilex subsp. ballota and Quercus faginea seedlings (arranged in rows 2:1) inoculated with T. melanosporum [ 21 ]. The experimental site is located in Gúdar-Javalambre county (Teruel province, eastern Spain, 1150 m a. s. l.).…”

“…Truffles are harvested by the owner once a week throughout the fruiting season (November to March). Each year, when the fruiting season is over, the soil shallowly tilled, and a peat-based substrate is applied in ten spots around each tree [ 21 ]. The orchard is irrigated with a sprinkling system from April to October during the dry periods with scarce rainfall.…”

“…Peat-based amendment is aimed at increasing fruiting depth and shape of FBs [ 21 ]. In the experimental site, the peat-based amendment is being applied by the grower following the most common procedure used in Spain.…”

“…In the experimental site, the peat-based amendment is being applied by the grower following the most common procedure used in Spain. The localized application of peat-based substrate around the host trees involves digging tronconical holes about 25 cm deep, filling them with about 1.5 L of a European Sphagnum peat-based substrate (Turbatruf ® from Projar, Quart de Poblet, Spain): A black peat—white peat—coir—perlite mix 11–5–3–1, with pH raised to 7.5) and re-covering the substrate with soil [ 21 ]. Grinded ripe truffle FBs are mixed with the substrate before being incorporated into the soil.…”

“…The causal models were built considering the linkages between the studied characters and the sequential morphogenetic stages of truffle FBs: fruiting depth linked to the mating process, weight and shape linked to the growing stage, and spore maturity linked to maturation [ 1 , 7 , 8 ] ( Table 1 ). We hypothesized that: (i) fruiting depth would have a positive effect on weight and maturity, because soil depth buffers extreme values in temperature and water content, which are particularly variable in Mediterranean climates [ 18 , 19 ]; (ii) no relationship between weight and maturity would appear, because dogs usually localize full-developed ripe FBs of sizes from less than 10 g to more than 100 g; (iii) shape of small FBs would we more rounded, because they need to make and occupy less soil volume and are less likely to face mechanical constraints during growth; (iv) in FB clusters, the weight of the largest FB would show a negative relationship with the weight of the remaining FBs, due to the local resource depletion or inhibition mechanisms hypothesized by Moore et al [ 20 ]; and (v) differences among soils and with substrate would affect relationships among FB development characters, since soil properties and localized substrate amendments are able to influence these characters [ 21 ].…”