Back to December 2012

Pecan Truffle Research Underway in Texas


Figure 1. A whole truffle found in a Texas pecan orchard (a), above. Washing and cleaning the truffles reaveals an orange-brown color of the outer ‘skin’ (b), right Cross section through a pecan truffle shows the marbled pattern of cream and light brown internal tissue (c), bottom left.

Figure 1. A whole truffle found in a Texas pecan orchard (a), above. Washing and cleaning the truffles reaveals an orange-brown color of the outer ‘skin’ (b), right Cross section through a pecan truffle shows the marbled pattern of cream and light brown internal tissue (c), bottom left.

The word ‘truffle’ often evokes an image of elegant culinary items including the expensive garnish or flavoring of fine European cuisine. Although the aromatic, edible fungal fruiting structures that are known as truffles are more often associated with European countries, North America has several species that naturally grow in forests across the continent.

One such truffle is called Pecan Truffle (scientific name: Tuber lyonii, earlier known as Tuber texense) because it frequently grows in association with the roots of both native and cultivated pecan (Carya illinoinensis) trees. The fungus and healthy tree roots live in a symbiosis that provides benefits to both organisms as well as yielding edible fruits for various animals.

Figure 2. Roots of pecan trees form a mutually beneficial symbiosis with several fungi, including Tuber lyoinii. This relationship is known as ectomycorrhizal symbiosis. Ectomycorrhizal roots (i.e., roots in symbiosis with fungi) can be recognized as highly branched, healthy root tips that are thickened and are lighter in color. DNA analyses help us identify the suite of fungi that are present in ectomycorrhizal root tips. Even when truffles are not found in the ground, DNA sampling of pecan roots can help us locate T. lyonii fungus.

Figure 2. Roots of pecan trees form a mutually beneficial symbiosis with several fungi, including Tuber lyoinii. This relationship is known as ectomycorrhizal symbiosis. Ectomycorrhizal roots (i.e., roots in symbiosis with fungi) can be recognized as highly branched, healthy root tips that are thickened and are lighter in color. DNA analyses help us identify the suite of fungi that are present in ectomycorrhizal root tips. Even when truffles are not found in the ground, DNA sampling of pecan roots can help us locate T. lyonii fungus.

For centuries, humans have enjoyed truffles as rare delicacies with exquisite aromas. However, their rarity in nature and high price meant few could afford them. These characteristics of truffles have only added to the allure, mystery and the fascination for them. Indeed, most of us are content with the chocolate ‘truffles’ that are somewhat more easily available without realizing that the term truffle, which comes from the Latin word ‘tuber,’ originated because of the truffle fruiting body.

Pecan truffles (Figs. 1a, 1b, and 1c), like other truffles, are the reproductive fruiting portion of a fungus that grows in a mutually beneficial relationship with live tree roots (Fig. 2). The species has been documented growing naturally across eastern and southern North America, from northern Mexico to Quebec and along the Gulf Coast to Florida to as far west as the Rocky Mountains (Trappe et al. 1996). Tuber lyonii has been found in native oak-hickory (QuercusCarya) forests as well as under pecan or oak trees in home yards and lawns, cultivated orchards, and other areas where these trees grow. When ripe and ready for dispersing its spores, truffles release a strong aroma to attract mammals who eat them and subsequently spread the spores. It is for this reason that pigs and dogs are frequently used to locate the elusive, below-ground fruiting bodies. Although one must keep the animal from eating the truffle!

Figure 3. Pecan orchards can be an ideal location for finding pecan truffles although the truffles are also found in association with pecan and oak trees in other settings such as home gardens.

Figure 3. Pecan orchards can be an ideal location for finding pecan truffles although the truffles are also found in association with pecan and oak trees in other settings such as home gardens.

Pecan orchards (Fig. 3) can be an ideal habitat for pecan truffles, which can sell in local markets for approximately $150-200 per pound (1lb = 454g). However, none of the previous 6 records (spanning from 1958 to 1997) of truffle locations within Texas represented pecan orchards. Additionally, no vouchered collections of this truffle had been made in the state since 1997. Considering the hypogeous (i.e., below the soil surface) nature of the truffles, it is not surprising that they are not encountered more often. In other states, pecan growers sometimes notice them in pecan sorting areas, but the truffle has remained elusive in Texas pecan orchards until now.

Figure 4. Map of Texas showing counties where pecan truffles (Tuber lyonii) have been located or searched-for recently. Green dots (Lamb, Wichita, Brown, Williamson, Bastrop, and Burleson Counties) indicate locations where truffles were found by us in November 2012. Five of these six sites were pecan orchards. Blue dots represent orchards that were searched at the same time but truffles were not found there. Red dots show counties from where truffles were reported by others from non-orchard sites between 1979 and 1997. Additionally, the first recorded truffle in Texas (Heimsch 1958) was found in Travis County (not marked on this map) in a planting bed.

Figure 4. Map of Texas showing counties where pecan truffles (Tuber lyonii) have been located or searched-for recently. Green dots (Lamb, Wichita, Brown, Williamson, Bastrop, and Burleson Counties) indicate locations where truffles were found by us in November 2012. Five of these six sites were pecan orchards. Blue dots represent orchards that were searched at the same time but truffles were not found there. Red dots show counties from where truffles were reported by others from non-orchard sites between 1979 and 1997. Additionally, the first recorded truffle in Texas (Heimsch 1958) was found in Travis County (not marked on this map) in a planting bed.

Recently, we surveyed several pecan orchards and other habitats to investigate the presence and distribution of pecan truffles in Texas. For this initial survey, we selected orchards representing various management practices and geographical locations within the state. Out of the 8 counties we visited (blue and green dots combined; Fig. 4) during the first week of November 2012, truffles were found in 6 counties (green dots). Five of the 6 locations where we found truffles were pecan orchards whereas 1 location represented a home lawn. Red dots on the map indicate counties from which truffles had been collected by others between 1979 and 1997, but no information on the exact location or the quantity and quality of their collections is available.

Figure 5. Truffle dogs can reduce search-time and maximize harvest of ripe truffles. Bailey, a selftrained truffle dog from Lamb County, Texas, digs to find truffles.

Figure 5. Truffle dogs can reduce search-time and maximize harvest of ripe truffles. Bailey, a selftrained truffle dog from Lamb County, Texas, digs to find truffles.

Our survey was conducted with the assistance of truffle dogs. While Ilsa, a pay-for-service dog from Oregon, was specially trained by her handler Kris Jacobson to find truffles, Bailey (from Lamb County, TX; Figs. 5, 6, 7, and 8) seems to have trained herself to find truffles in her backyard. She, however, loves to consume the truffles upon locating them! Since the discovery that these are pecan truffles, Aletha and Kenny Birkelbach (Bailey’s owners) have begun training Bailey to relinquish the truffles in exchange for dog-treats or other rewards. While it is possible to find truffles by raking in the areas where they are suspected or known to grow, the raking method is very time consuming, causes more disturbance to the soil, and results in a mixture of mature and immature truffles. On the other hand, dogs cue into ripe truffles and can reduce the harvest time considerably (Smith et al. 2012).

Figure 6. After a truffle dog locates the underground truffles, left, one can remove the top 3-5 cm of soil to find them as loose, potato-like structures. Truffles should be washed and cleaned before they are consumed fresh. Tests show that cleaned pecan truffles can be stored in a refrigerator for up to 2-3 weeks without a significant loss of aroma and texture.

Figure 6. After a truffle dog locates the underground truffles, left, one can remove the top 3-5 cm of soil to find them as loose, potato-like structures. Truffles should be washed and cleaned before they are consumed fresh. Tests show that cleaned pecan truffles can be stored in a refrigerator for up to 2-3 weeks without a significant loss of aroma and texture.

It is possible that the ongoing drought has affected truffle yields this year or perhaps early November is not the peak truffle season in Texas. It is also possible that orchard management practices influence truffle yields. We collected approximately 150g of truffles during our survey. The 5 previously reported collections mentioned above were made in April, June, August, September and November, but it is not known how many truffles were found during each of those collections. Regardless, it is encouraging to have located potential truffle grounds in several counties within the state.

We will continue orchard surveys in Texas over the next year to estimate natural yields across seasons and geographic locations. Simultaneously, we are conducting experiments with pecan seedlings inoculated with truffle spores for transplanting into orchards (Figs. 9, 10, and 11). It is to be noted that similar to pecan trees, pecan truffles may take up to 7-8 years to fruit after inoculation if they are transplanted in soils devoid of naturally occurring T. lyonii fungus. Additionally, like wine grapes, different truffle species display diverse organoleptic properties influenced by genetics and the local conditions in which the truffles are grown. Many European truffle species have been characterized by the content of their volatile compounds and aromas, however, no such characterizations have been reported for the pecan truffle. To improve their culinary reputation and value, we are conducting aromatic chemical and sensory analyses on pecan truffles to characterize them against the more familiar European truffle species/products.

While many research questions remain to be answered, methodically documenting the naturally growing truffles in Texas pecan orchards is a significant step.

Thus far, pecan growers and other plant and food lovers have shown great enthusiasm for pecan truffles by graciously assisting us with this exciting project. Looking ahead, our goals are to increase awareness about pecan truffle as a specialty crop, develop methods for producing inoculated seedlings to maximize the symbiosis between pecan roots and pecan truffle, test management methods to increase natural truffle yields, and continue truffle surveys to assess the potential for dual cropping of pecans and truffles.

Research has shown that pecan trees can also support other species of truffles besides pecan truffles (Benucci et al. 2011) indicating that it might be possible to use pecan trees as hosts for European truffle species as well. At the same time, some truffle look-alikes (Figs. 12a and 12b) also grow in association with pecan trees. The fruiting bodies of these fungi often are somewhat softer, have a tapered base that attaches the fruiting structure to the fungal mycelium (i.e., the collective body of a fungus), and have dark purple to black interiors (Fig. 12b) as opposed to the cream and light brown marbled interior of pecan truffle (Fig. 1c). False truffles are not suitable for human use, however.

Figure 10. Other below-ground fungal fruiting structures can superficially resemble pecan truffles. These ‘false-truffles’ are generally softer, have a tapered base (left), and have dark purple to black interiors (right).

Figure 10. Other below-ground fungal fruiting structures can superficially resemble pecan truffles. These ‘false-truffles’ are generally softer, have a tapered base (left), and have dark purple to black interiors (right).

If you locate pecan truffles around your trees, please contact us to help confirm the identity. We would like to add the information to our database of location, time of year, and size of harvest. If you enjoy these delicacies in your meals (by washing, cleaning, and slicing the truffles thinly to use as fresh garnish on hot pasta, eggs, potatoes, or squash), please share your culinary and sensory experience with us!

Acknowledgments

We are grateful to the Specialty Crop Block Grant Program as administered by the Texas Department of Agriculture for providing the funding for this work. Additionally, we sincerely thank Cindy Wise, Dr. Tim Brenneman, Dr. LJ Grauke, Keith Kubenka, Gerald and Geri Kline, Aletha and Kenny Birkelbach, Bailey (Cocker Spaniel and a natural truffler belonging to the Birkelbachs), Eileen and Gene Niswander, Andy Sherrod, Mike Adams, Jake Montz, Hal Berdoll, Buzz White, Gary Lehmann, Kris Jacobson and her dog Ilsa, Charles Lefevre, Mike Berry, and Lynn Johnson for their wonderful help. Many other colleagues and collaborators also continue to assist us.


Literature Cited
Benucci, G.M.N., Bonito, G., Baciarelli-Falini, L., and Bencivenga, M. 2011. Mycorrhization of pecan trees Carya illinoinensis. with commercial truffle species: Tuber aestivum Vittad. and Tuber borchii Vittad. Mycorrhiza . DOI 10.1007/s00572-011-0413-z.
Heimsch, C. 1958. The first recorded truffle from Texas. Mycologia 50: 657-660.
Smith, M., Bonito, G., Sharma, J., Long, J., Davis-Long, B., and T. Brenneman. 2012. Pecan truffles (Tuber lyonii): what we know and what we need to know. Georgia Pecan Magazine 2012 Spring: 52-59.
Trappe, J.M., Jumpponen, A.M.J., and Cazares, E. 1996. Nats truffle and truffle-like fungi. 5. Tuber lyonii (= T. texense), with a key to the spiny-spored tuber species groups. Mycotaxon 60: 365-372.
Author Photo

Jyotsna Sharma, Brent Trela, Shi Wang, Matthew Smith and Gregory Bonito

Sharma, Trela and Wang are with the Department of Plant and Soil Science, Texas Tech University, Lubbock, TX. Smith is with the Department of Plant Pathology, University of Florida, Gainesville, FL. Bonito is with the Department of Biology, Duke University, Durham, NC.