Planning a truffière
Truffles are the ‘fruit’ of fungi that live in the soil in association with the roots of several tree species.
The Western Australian truffle industry is based predominately on the French black truffle or Périgord truffle (Tuber melanosporum), grown in association with oak and hazelnut trees. The trees must be inoculated with selected strains of the fungi before being planted out into orchards (or truffières). It takes four to six years after planting before the first truffles are likely to be harvested.
The first commercial plantings of truffle orchards in Western Australia occurred in 1997, with the first truffle harvested in 2001. Truffles are currently grown mostly in the South West region, particularly around Manjimup. It is not known if production will be successful in other areas, but inoculated oak and hazelnut trees have been planted in the Perth Hills and at Toodyay, north-east of Perth, as well as Margaret River, Walpole and Denmark.
The main production area is based around Manjimup and Pemberton, at latitude 34°S and an altitude of 200 to 280m. This is much closer to the equator than most truffle areas in the world.
Truffles grow best with mild summers with an average maximum temperature from 16.5 to 25°C, mid-winter average minimum temperatures between 0 and 10°C and when the soil temperature drops to 9°C. Manjimup-Pemberton has an average maximum summer temperature of 26.1°C and an average minimum winter temperature of 7.3°C. Rainfall area averages 1100mm, mainly from April to November.
Truffles grow best on well-drained alkaline soils with a good level of calcium. The acidic soils in the Manjimup-Pemberton area require liming to increase pH to greater than 7.5 (measured in water). Dolomite lime supplies magnesium as well as calcium.
Soils should be ripped before planting to disturb any hardpan or compacted layers and improve drainage. The soils in the Manjimup area contain a lot of gravel which provides good drainage but this can affect the shape of the truffles. Truffles obtained from soils with less gravel are rounder and have better shape.
Truffles are grown in association with a host crop, most commonly hazelnuts (Corylus avellana), or oaks such as:
- English - Quercus robur
- cork - Quercus suber
- holm/holly - Quercus ilex.
The Manjimup climate is not optimal for hazelnuts and as such they have low economic value as a nut tree. Mechanical harvesting of hazelnuts can damage the valuable truffles. Therefore, common named hazelnut varieties are not normally used for inoculations. It is possible to grow truffles on the roots of some common European woodland trees, but this is not done commercially.
Inoculated hazelnut and oak plants for commercial growers are available from specialised nurseries. If planting stock is being brought from interstate, Quarantine WA biosecurity requirements must be met.
The exact method of inoculation of truffles is a trade secret. To prevent bacterial contamination inoculation must be done on germinating seeds. Seeds are collected from hazelnuts and oaks in autumn and inoculated with spores. The growth of truffle mycorrhizae (fungal threads) is visible on the roots of inoculated trees in the nursery and plants are ready for planting after about 14 months.
Types of truffle
There are over 200 truffle species worldwide with about 70 edible species. Only a small number of these are cultivated or harvested from the wild for consumption. The French black truffle (Tuber melanosporum) is one of the most sought after and highly valued. The highest prices are received for the Italian white truffle (Tuber magnatum), but its cultivation has not yet been mastered.
Other truffles are marketed but generally for a much lower price. Other, less desirable truffles and some of their defining features include:
- Winter truffle (Tuber brumale): fragile skin that is easily removed by brushing, broader white veins compared to T. melanosporum and T. indicum.
- Burgundy truffle (Tuber aestivum): pyramid-shaped warts on the skin surface, brown to black internal colour.
- Chinese truffle (Tuber indicum): variable appearance, can be very similar to T. melanosporum, distinguishable spores under microscope.
It is possible to confuse different truffle species in the market. Testing to determine the type can be done using DNA analysis or microscopic inspection. Care must be taken when inoculating trees to ensure the correct truffle spores are used. Different species of truffle, and indeed other fungi, can compete in the soil resulting in reduced yield of the desired truffle.Tuber brumale, in particular, is very competitive. In Europe, native fungi have competed with truffles in cultivated areas.