Taxonomy and Phylogeny
Terfezia boudieri is a kind of edible desert truffles. In La Truffle, A. Chatin first described Terfezia boudieri in 1892. There are several species sharing the same common name ‘desert truffle’ such as T. arenaria, T. canariensis, T. claveryi, T. fanfani, T. olbiensis, Tirmania ninea and Loculotuber gennadii. The name of Terfezia comes from the Arabic “terfez” in North Africa (Rodríguez, 2008).
T. boudieri belongs to kingdom Fungi, phylum Ascomycota, class Pezizomycetes, order Pezizales, family Pezizaceae, and genus Terfezia. In family level, the classification of Terfezia is still on debate. The desert truffles (include Terfezia) were traditionally grouped into Terfeziaceae family, within the order Tuberales, based on their morphological similarities. Molecular phylogenetic studies reflected that some truffles were closely related with family of Pezizales. Normal and Egger (1999) suggested that T. arenaria and T. terfezioides belong to Pezizaceae family by examining their ITS region, 18s and 28s rDNA genes. In the same year, Percudani et al., (1999) sequenced the 18S rDNA from nine species including three families: Tuberaceae, Terfeziaceae, and Balsamiaceae. The result showed that genus Terfezia were nested within Pezizaceae. Later, restriction fragment length polymorphism (RFLP) and ITS of the nuclear rDNA were studies for several Terfezia and Tirmania species. As a result, they both belonged to Pezizaceae family with a close genetic relationship between each other and are also monophyletic.
Morphology
T. boudieri are hypogeous fungi and have potato shape fruiting bodies with a size of 2-6 cm diameter (Ammarellou et al., 2007) (Fig.1-A). The shape of T. boudieri is described as subglobose, turbinate or obpyriform. At the beginning of its growth, the peridium is usually yellowish white with the thickness of 1-2 mm and accompanies with a solid, succulent gleba that displays colors from whitish to pale pink. When the fungus reaches its maturity, the thick peridium turn into black and the gleba become dark for its pinkish color, which will turn into yellowish-orange if exposed to air. Eventually, the fungus begins to crack the surface of the ground by forming a bump-like structure (Fig.1-B) (Ammarellou et al., 2007). In addition, no distinct odour, faint or mild taste is produced. To distinguish T. boudieri from the other species relies on its relatively large size (average sized potato big, as mentioned above), grayish brown color, and the habitat of high pH calcareous sandy soils (Fig.1-A) (Ammarellou et al., 2007). Another identification character is it always found that has an association with Helianthemum species plants.
The shape of its asci is subglobose, ovoid or pyriform with 60 to 110 µm in length and 50 to 80 µm in width. There are 4 – 8 spores in each asci(Fig.2). The ascospores are yellow to ochre in color, spherical in shape and 20 to 25 µm in diameter with the ornaments. At maturity, there are truncated warts on the skin of the ascospores that are generally 2 µm in length and are attached to hemispheric and conical shape-like spines (Fig.2). Those warts form to crests and irregular interconnected reticulum. In Melzer’s reagent, the spores display lightly orange to yellow- brown, and more angular of the ornaments than seen in potassium hydroxide (Rodríguez, 2008).
Ecology
Life cycle
Although the life cycles of Terfezia has not been completely elucidated (Bejerano et al., 2004), it is well known that truffle spores are spread by animals including: dogs, pigs and squirrels, etc. The spores dispersed by those animals’ excreta after eaten by them (Belliana-Agostinone et al., 1987). Terfezia species could be explained by the four stages: Firstly, primary homokaryotic mycelium is formed by the germination of ascospores. Secondly, the mycelium will infect host plants in soil if there is host plant available nearby. Otherwise, secondary mycelium will be formed by the plasmogamy. Thirdly, the continuous growth of fungus will lead to a fruit bodies constituted by heterokaryotic hyphae. Fourthly, ascospores will be formed by meiosis (Bejerano et al., 2004).
Distribution
Generally, desert truffles are grown in arid and semi arid areas of the Mediterranean Region, North Africa, and the Middle East with mycorrhizal association with Helianthemum species or plants like Cistus species, oak trees and pines etc. T. boudieri is distributed in Canary Islands, Morocco and North Africa, east to Iraq, Cyprus , Arabian Peninsula, and Bahrain Islands. It is mycorrhizal associated with plants listed as below: Cistus albidus; C. salviifolius;C. monspeliensis; Fumana procumbens;Halimium halimifolium; Helianthemum apenninum; H.canariensis; H. eremophilum; H. hirum car. Deserti; H. ledifolium;H. kahiricum; H. lippii; H. salicifolium;Tuberaria guttata;Plantago albicans; Artemisia monosperma; Schismus barbarous. In addition, there also are reports indicating that the mycorrhizal association exists between Terfezia and Stipagrostis spp. in southern Africa, where Cistaceae is absent (Kiraly & Bratek, 1992).
Mycorrhizal association growth habit
As symbiont fungi, T. boudieri has been demonstrated to get their nutrition from annual and perenial Helianthemum spp. and other Cistaceae spp., which are distributed throughout the Mediterranean Basin, northern Africa, Saudi Arabia and the United Arab Emirates. There is research studying on the mycorrhizal association between the T. boudieri and Helianthemum sessiliflorum. The research indicated that H. sessiliflorum mycorrhizal plants exhibited a higher photosynthetic activity rate than non-mycorrhizal plants. Another research indicated that the mycorrhizal association supported the host to survive and establish in unfavorable conditions (Amaranthus and Perry, 1989). Later, the research conducted by Turgeman (2011) indicated that mycorrhizal plants make more biomass than those not mycorrhizal ones under harsh environment because of their low energy requirement for photosynthesis activation.
T. boudieri have a very similar habitat as T. canariensis and T. claveryi in the desert truffle group. They are all spring species and grow in basic soils. Another kind of desert truffle T. arenaria is also a spring species but grows in acid, sandy and moist soil. T. fanfani is also a spring species that can grows in acid, sandy or more compact soils. It can be grown earlier than T. arenaria that can be found even in January. These desert truffles and their associated host are very important to the Mediterranean ecology. Their symbiotic relationship has been described in Pak’s paper as that the host plant sedges occur at the same time when the truffles appear, otherwise they won’t exist. They play an essential role in the maintenance of shrub lands and grasslands to prevent desertification and erosion (Honrubia et al., 1992).
Another part of growth habit worth to mention is that although they grow in semi-arid regions, desert truffles still need a certain amount of water to grow up. Rains in August, September, January and February are particularly helpful to their development.
Overall Biology and Relevance for Humans
Generally, people cherish truffles because their pleasant flavor, delicious taste, and health benefits. Desert Truffles are not he same precious truffles used sparingly in French dish, they are food. In Arab countries, desert truffles are very appreciated and can be found in local market with common name of Terfass, Terfess or Terfez. Terfezia are known and traded by ancient Greeks and Romans.
Nutrition value
Especially, in Tunisian, T. boudieri has been appreciated as an edible and important food. There was a research on biochemical properties of T. boudieri, which indicated that the fruiting body of this species contains 15.4% total sugars, 2.02% soluble sugars, and 10.5% protein on a dry weight basis. It is rich in potassium, calcium, phosphorus and magnesium. According to this study, T. boudieri present a high nutritional for humans (Slama et al., 2009). Unlike the other truffles, there is not a lot of researches reveals its aroma property and therapeutic functions beside its nutritional importance. However, there is one paper that indicates that T. boudieri is not only a great source of some essential minerals and fatty acids, but also this species is rich in antioxidant and antibacterial compounds which affect humans health positively (Hamza et al., 2013).
Cultivation
In ancient time, these hypogeous fungi were considered as God-given food because of the difficulties in cultivation. Recently, these desert truffles, their botany ecology, physiology, and utilization have received more attention. The potential for using the vast desert lands to produce commercial truffles encouraged several countries to initiate research programs. In 1970s, the first truffles cultivation was made in France (Chevalier and Grente, 1979). After that, more cultivation tests were conducted (Chevalier and Frochot, 1997). Truffle farms are established in Europe, Australia, North America, China and New Zeland (Hall et al., 2007; Morte et al., 2008). Researches on truffles cultivation are very important to support truffles farm development. Generally, it cost 12 months to produce marketable desert truffles if management is proper conducted. Helianthemum species plants are used for host plant mycorrihized with different kind Terfezia ruffles. Slama (2010) used Helianthemum sessiliflorum as the host plants to grow T. boudieri in two soil types ：gypsy and sandy loamy. Two cultivation methods were used which were transplantation of inoculated plants maintained in greenhouse and seedling of inoculated H. sessiliflorum maintained directed in field, respectively. The result reflected that direct inoculation ofof seeds in field performed better than transplantation.
In addition, rainfall plays an important role in truffles production. Rainfall dependence of desert truffle fruiting is one of the most influential factors that need to be considered for a successful cultivation. The best season for planting is spring because it has the moderate temperatures, the abundance of precipitation and long photoperiod. In the region of Mucria, with a rainfall of between 350 to 400 mm, the irrigation system is not necessary for the production of desert truffle (Honrubia et al., 2003). However, in arid and semiarid climates, irrigation system is necessary for the dry years when the rain is less than 150 mm. Weeds could be another problem that needs to be considered about. Generally, Weeding work is conducted after third year of plantation, which could avoid intense competition that will limit desert truffle production. Nevertheless, the production of desert ruffles is very sensitive to environment conditions, which always display a production fluctuation among years.
