White mulch and irrigation increase black truffle soil mycelium when competing with summer truffle in young truffle orchards

Effects of Black and White Mulch on Mycelial Growth of Tuber Species in Korean Field Environment

Truffles, belonging to the genus Tuber, are ectomycorrhizal (ECM) fungi that form underground ascocarps and primarily establish symbiosis with oaks and hazels. The cultivation of Tuber spp. involves transplanting inoculated seedlings that have formed ectomycorrhiza with Tuber species, with mulching being effective for truffle cultivation. In this study, we investigated the effects of mulching on the mycelial growth of four Tuber species (T. himalayense, T. koreanum, T. melanosporum, and T. borchii) in the Korean natural environment, highlighting the potential for Korea as a truffle cultivation site. We developed and tested species-specific primers for quantifying the soil mycelial biomass of Tuber spp. by qRT-PCR, determined the superior mulch color for mycelial growth, and identified the Tuber species exhibiting the highest growth rate in the Korean field environment. Our results demonstrated that white mulch significantly enhanced mycelial growth in Tuber species than black mulch, likely owing to its ability to maintain low soil temperatures, control weeds, and improve host plant growth. Among the Tuber species, T. himalayense showed the greatest growth potential in the Korean natural environment. Additionally, a significant and positive correlation was observed between the mycelial biomass of Tuber species and the growth of inoculated seedlings, as measured by the total stem length and the number of leaves, thereby indicating the importance of symbiosis between ECM fungi and host plants. This study provides valuable insights into truffle cultivation in Korea and highlights the potential of using white mulch to promote mycelial growth, thereby contributing essential data for understanding the appropriate environmental conditions for Tuber spp. cultivation in Korea. Further study is needed to assess the long-term impact of mulching and to explore the effectiveness of other mulching materials.

European Tuber melanosporum plantations: adaptation status in Hungary, mycorrhizal level, and first ascocarp detection in two truffle orchards

Tuber melanosporum is one of the most economically important truffle species. Besides harvesting from its natural habitats, this truffle can also be extensively grown through artificial cultivation. However, the natural habitat of T. melanosporum has drastically declined, and the demand for the truffle in society is rapidly increasing. Therefore, enhancing production in truffle orchards by seeking new places for the establishment and regularly monitoring its adaptability might be an effective method for ensuring the sustainable productivity of the species. As a truffle science, recent information is important to further success in the growth of this truffle species. This study reports mycorrhization level and ascocarp production in two truffle plantations in Hungary. The estimated mycorrhization levels of the host plants were 43.36% in Biatorbágy and 42.93% in Jászszentandrás plantations. In March 2020, the 6-year-old and 18-year-old T. melanosporum plantations yielded around 100 g and 980 g of ascocarps, respectively. In general, adaptation of mycorrhizal seedlings in Hungary may become more effective as present management practices improve.

The fall of the summer truffle: Recurring hot, dry summers result in declining fruitbody production of Tuber aestivum in Central Europe

Global warming is pushing populations outside their range of physiological tolerance. According to the environmental envelope framework, the most vulnerable populations occur near the climatic edge of their species' distributions. In contrast, populations from the climatic center of the species range should be relatively buffered against climate warming. We tested this latter prediction using a combination of linear mixed effects and machine learning algorithms on an extensive, citizen-scientist generated dataset on the fruitbody productivity of the Burgundy (aka summer) truffle (Tuber aestivum Vittad.), a keystone, ectomycorrhizal tree-symbiont occurring on a wide range of temperate climates. T. aestivum's fruitbody productivity was monitored at 3-week resolution over up to 8 continuous years at 20 sites distributed in the climatic center of its European distribution in southwest Germany and Switzerland. We found that T. aestivum fruitbody production is more sensitive to summer drought than would be expected from the breadth of its species' climatic niche. The monitored populations occurring nearly 5°C colder than the edge of their species' climatic distribution. However, interannual fruitbody productivity (truffle mass year^-1 ) fell by a median loss of 22% for every 1°C increase in summer temperature over a site's 30-year mean. Among the most productive monitored populations, the temperature sensitivity was even higher, with single summer temperature anomalies of 3°C sufficient to stop fruitbody production altogether. Interannual truffle productivity was also related to the phenology of host trees, with ~22 g less truffle mass for each 1-day reduction in the length of the tree growing season. Increasing summer drought extremes are therefore likely to reduce fruiting among summer truffle populations throughout Central Europe. Our results suggest that European T. aestivum may be a mosaic of vulnerable populations, sensitive to climate-driven declines at lower thresholds than implied by its species distribution model.

Design and Validation of qPCR-Specific Primers for Quantification of the Marketed Terfezia claveryi and Terfezia crassiverrucosa in Soil

Desert truffle crop is a pioneer in southeastern Spain, a region where native edible hypogeous fungi are adapted to the semiarid areas with low annual rainfall. Terfezia claveryi Chatin was the first species of desert truffle to be cultivated, and has been increasing in recent years as an alternative rainfed crop in the Iberian Peninsula. However, its behaviour in the field has yet not been investigated. For this purpose, specific primers were designed for the soil DNA quantification of both T. claveryi and Terfezia crassiverrucosa and a real-time qPCR protocol was developed, using the ITS rDNA region as a target. Moreover, a young desert truffle orchard was sampled for environmental validation. The results showed the highest efficiency for the TerclaF3/TerclaR1 primers pair, 89%, and the minimal fungal biomass that could be reliable detected was set at 4.23 µg mycelium/g soil. The spatial distribution of fungal biomass was heterogeneous, and there was not a direct relationship between the quantity of winter soil mycelium and the location/productivity of desert truffles. This protocol could be applied to tracking these species in soil and understand their mycelial dynamics in plantations and wild areas.

Microbial communities of ascocarps and soils in a natural habitat of Tuber indicum

Truffles are the fruiting bodies of hypogeous fungi in the genus Tuber. Some truffle species usually grow in an area devoid of vegetation, called brûlé, but limited knowledge is available on the microbial composition and structure of them. Here, we investigated the bacterial and fungal communities of Tuber indicum ascocarps and soils inside and outside a characteristic brûlé from a poplar plantation with no truffle production history in northeastern China using a high-throughput sequencing approach. A predominance of members of the bacterial phylum Proteobacteria was observed in all samples. Members of Bacillus were the main genera in the ascocarps, while members of Lysobacter and unidentified Acidobacteria were more abundant in the soil. In addition, members of Gibberella, Fusarium, and Absidia were the dominant fungi in the ascocarps, while members of Tuber were enriched in the ascocarps and soils inside the brûlé. Some mycorrhization helper bacteria (Rhizobium) and ectomycorrhiza-associated bacteria (Lysobacter) were detected, indicating their potential roles in the complex development of underground fruiting bodies and brûlé formation. These findings may contribute to the protection and cultivation of truffles.

Truffle species strongly shape their surrounding soil mycobiota in a Pinus armandii forest

Truffles contribute to crucial soil systems dynamics, being involved in plentiful ecological functions important for ecosystems. Despite this, the interactions between truffles and their surrounding mycobiome remain unknown. Here, we investigate soil mycobiome differences between two truffle species, Tuber indicum (Ti) and Tuber pseudohimalayense (Tp), and their relative influence on surrounding soil mycobiota. Using traditional chemical analysis and ITS Illumina sequencing, we compared soil nutrients and the mycobiota, respectively, in soil, gleba, and peridium of the two truffle species inhabiting the same Pinus armandii forest in southwestern China. Tp soil was more acidic (pH 6.42) and had a higher nutrient content (total C, N content) than Ti soil (pH 6.62). Fungal richness and diversity of fruiting bodies (ascomata) and surrounding soils were significantly higher in Tp than in Ti. Truffle species recruited unique soil mycobiota around their ascomata: in Ti soil, fungal taxa, including Suillus, Alternaria, Phacidium, Mycosphaerella, Halokirschsteiniothelia, and Pseudogymnoascus, were abundant, while in Tp soil species of Melanophyllum, Inocybe, Rhizopogon, Rhacidium, and Lecanicillium showed higher abundances. Three dissimilarity tests, including adonis, anosim, and MRPP, showed that differences in fungal community structure between the two truffle species and their surrounding soils were stronger in Tp than in Ti, and these differences extended to truffle tissues (peridium and gleba). Redundancy analysis (RDA) further demonstrated that correlations between soil fungal taxa and soil properties changed from negative (Tp) to positive (Ti) and shifted from a moisture-driven (Tp) to a total N-driven (Ti) relationship. Overall, our results shed light on the influence that truffles have on their surrounding soil mycobiome. However, further studies are required on a broader range of truffle species in different soil conditions in order to determine causal relationships between truffles and their soil mycobiome.

Truffle Market Evolution: An Application of the Delphi Method

Background: The objective of this study was to analyze the current situation of the truffle sector in the main producing countries of the Mediterranean area. Additionally, we identified the challenges for the future and the priority actions to develop the truffle sector in the region. Methods: We used a Delphi process approach, and we selected a total of 17 expert panelists in different positions within the supply chain of the target countries (Spain, France, Italy, Croatia, and Greece). Results: The results obtained allowed us to have a complete description of the current truffle supply chain. We confirmed an evolution of the sector due to the cultivation success of several Tuber species. The maturity of the sector has produced shifts in the roles that form the traditional truffle supply chain operators. We confirmed the trend of a decrease of collectors that hunt truffles in the wild and sell to small travelling buyers, whilst truffle hunters that collect for farmers and specialty wholesalers are emerging. However, a trend of truffle price decrease in the last few years has alerted the sector. Conclusions: As production increases due to truffle cultivation, it will be necessary to promote truffle consumption. We identified actions to develop the truffle sector: (a) strengthen the link between truffles, tourism, and gastronomy; (b) increase the effort at European level for the recognition of truffle production, helping to develop truffle culture and marketing; (c) increase the awareness and consumption of truffles among consumers; and (d) develop tourism workshops for truffle farmers.