Propagation of edible Pecan Truffle (Tuber lyonii) in pecan nurseries

View the project final report

• 2014 annual report

Commodities

• Nuts: pecans

Practices

• Crop Production: biological inoculants, double cropping, multiple cropping
• Production Systems: general crop production
• Soil Management: soil microbiology

Introduction

The pecan (Carya illinoinensis) is an economically important, native tree that is prevalent throughout the Southern USA. The USA produces >80% of the world’s pecans (worth $674 million in 2010) and the vast majority of pecans come from Southeastern states (Giesler, 2011). Although the pecan business has been extremely successful in recent years, the problems of alternate bearing trees, price fluctuations, and disease pressure remain problematic for growers (Anderson et al. 2012; Anderson & Cocker, 2012)

Pecan trees bear an exceptional nut crop in the canopy, but they also have an underutilized potential to yield a lucrative supplementary crop from their roots. The native pecan truffle (Tuber lyonii) is an ectomycorrhizal (ECM) fungus that forms a mutualistic symbiosis with pecan trees. Truffles are subterranean fungal fruiting bodies and T. lyonii is a native species that is related to the prized European truffles (Bonito et al., 2011). Symbiotic ECM fungi enhance plant health by increasing nutrient absorption, mitigating drought stress, and limiting root disease (Smith & Read, 2009).

Given their high culinary and economic value, truffles are the ultimate specialty crop. Valued at $160–320 per pound, pecan truffles are candidates for commercial production but have been neglected due to a lack of information about overall biology and production practices (Smith et al., 2012). However, pecan truffles are common and widespread in pecan-growing regions of the Southeast and some orchards can produce two or more pounds of truffles per acre per year (Smith & Brenneman, personal observation). This truffle fruits August to November on a variety of soil types. Unfortunately, like other symbiotic ECM fungi, pecan truffles cannot reproduce in the lab - they can only be cultivated with a living host tree.

Studies on the pecan truffle are timely because European truffle harvests have dwindled while global demand has grown. In the Pacific Northwest, interest in locally produced foods has driven a boom in the new truffle economy with >$300,000 of truffle income per year and additional revenues from associated businesses (Pilz et al., 2009). The pecan-truffle agro-ecosystem has the potential for even greater success due to the simultaneous harvest of pecans and truffles.

Like many other truffles, pecan truffles proliferate in habitats with soil disturbance, limited litter, and high soil pH so pecan orchards are an excellent truffle habitat (Bonito et al., 2011). Preliminary studies suggest that minor changes in nursery and orchard management could facilitate sustainable production of the pecan truffle with minimal costs to growers and positive impacts on trees. Production of this symbiotic, edible truffle will increase the sustainability of the pecan agro-ecosystem by providing important supplemental income. For nurseries, the production of truffle-inoculated pecan trees will ensure premium prices and allow the nurseries to sell to a wider audience that includes both pecan growers and homeowners. Lastly, the new truffle crop will generate regional economic benefits by spurring truffle-associated businesses such as truffle dog training, truffle marketing, and “food tourism” (Pilz et al., 2009).

The best approach to promote Tuber lyonii cultivation on pecans is to begin in the nursery. Data from European truffle production suggests that successful colonization of seedling roots with truffles is one of the most important factors in determining success of truffle orchards (Hall et al., 2007; Bonet et al., 2009). Accordingly, we are working with nurseries to:

1) identify the current distribution of the pecan truffle on seedlings in nurseries, and

2) develop protocols to inoculate pecan seedlings in nurseries with minimal changes in operating procedures.

Secondary objectives that developed over the course of the research project also included identify the main fungi that compete with Tuber lyonii in the nursery setting and determine whether Tuber lyonii is actually one species or actually part of a species complex.