Australasian Science: Australia's authority on science since 1938

The Truffle Hunter

Club-like roots indicate mycorrhizal infection.

Club-like roots indicate mycorrhizal infection.

By Stephen Luntz

Colin Carter is putting the production of French black truffles onto a scientific footing.

French black truffles are one of the most expensive legal items on the planet, selling for upwards of $1800 per kilogram at the farm gate. The fungi are so fragrant that small quantities can give flavour to an entire meal, but the original supply of the truffles has collapsed. Australians are racing to fill the gap, and science is proving essential.

In 1900 the forests of France produced 1000 tonnes of truffles per year. “Now, the total harvest is down to about 50 tonnes a year,” says Colin Carter. “We went to an annual truffle auction, where hunters arrive with their truffles in little bamboo baskets, and at that auction last year there was only about 50 kilograms of truffles for sale. The year before at the same event there was 200 kilograms.”

Spain has been filling some of the gap, but there is plenty of demand for Australian product if we can ramp up production. Currently we’re at 2 tonnes per year, a drop in the ocean compared with the potential.

Carter teaches horticultural science at Swinburne TAFE. Initially his interest was in using a variety of symbiotic fungi to bolster crops, but 6 years ago he met another teacher with an enthusiasm for truffles. “We got talking and I did some reading and research and got hooked.”

Australian native truffle species are not poisonous, but they’re also not very tasty. Attempts to inoculate native species of trees with imported truffles have proven fruitless, so the Australian industry involves imported Tuber melanosporum fungi on oak trees. The truffles are good for the trees, taking phosphorus that would be insoluble to the tree and converting it to a form that trees can absorb. In Australia’s low phosphate soils this can be invaluable. In return, the tree provides the fungus with sugars and other carbohydrates.

There are some advantages to the fact that the truffles are non-native species. Where European truffle farmers have to worry about a range of similar, but less tasty, species competing with the most valuable truffles, Australian farmers are almost guaranteed to produce the prized French black truffles.

That’s if they manage to produce truffles at all. In Europe, truffle farmers claim that 30–60% of infected trees produce truffles, but in Australia the average rate is 8%. Carter is helping to solve the mystery of why Australian truffle rates are so poor, noting that “the industry is still young”..

Truffles like well-drained soils with a pH of 8. In Europe, truffière plantations avoid acidic soils. However, in Australia this luxury is almost unachievable, so Australian farmers have demonstrated that the application of lime can make farming viable.

Carter has found that there is more to truffle cultivation than making soils alkaline. “We have to look at what techniques we are using – particularly pruning, cultivation and irrigation,” Carter says.

In France, truffles grow largely in areas where rainfall is low but relatively consistent through the year. Big summer storms make the summers wet by southern Australian standards, and farmers don’t use irrigation. Australian farmers irrigate, but Carter thinks they have gone about it the wrong way.

“I think they need to let the soil dry out for a while, say 20 days, and then give it a really big soaking, rather than regular smaller watering,” Carter says. “In Europe they initially cultivate the soil by deep ripping, letting in oxygen and water down to 60 cm below the surface. This breaks some of the roots, which I used to think was a bad thing, but it seems that just like pruning above the ground it causes a burst of growth in the root, and they can self-inoculate.”

Finding the best way to raise truffles is hard, as experiments take so long to bear fruit. It takes at least 4 years before the first truffles appear, and several years after that before crops become substantial. Partly as a result, truffle science is new, and mainly focused in Spain. The French have stuck with traditional methods, old myths and secrets while their production has collapsed.

Carter says that “no one really knows” why French production is down so much. Urbanisation of truffle farming regions has been a factor, and acid rain perhaps another one. Truffle spores have a waxy coating that allows them to remain dormant in the soil, but they need to pass through the digestive system of an animal to remove this coating and germinate. Hunting and exclusion of animals has helped farmers get to the truffles before animals, but at the price of future fungi generations.

Carter has experimented with chemical processing that mimics the effects of animal consumption, and believes he has found a way to improve inoculation success rates.

Another discovery is that sunlight is important for truffle growth. After 10 years, oak trees start to develop a canopy that keeps out too much light, and production can drop off just as it is hitting its stride. Early shaping of the boughs, so that the tree allows more light to reach the ground, can be crucial.

Carter had plans to become a vet after school, but a friend persuaded him to attend an open day at Burnley School of Horticultural Science (now part of Melbourne University), then Australia’s leading horticultural school. “I thought it was a girls’ school and didn’t want to go,” Carter says. However, as soon as he visited the campus he was hooked.

“I’d grown up where everything was recycled with a vegie garden and chooks, and I was always involved in that,” says Carter. “As soon as I saw Burnley I loved it, and applied straight away.” After a 3-year diploma he founded his own business, but eventually felt the urge to teach and started at Swinburne.

Carter’s initial area of interest was vesicular arbuscular mycorrhiza (VAM), a form of fungi that colonises the roots of 80% of plants. Their microscopic tubes or hyphae grow further out into the soils than plant roots, and bring nutrients back to the plant while being fed carbohydrates in return. They are particularly valuable for plants in nutrient-poor soils. “I compared organic farming techniques with mineral fertilisers and found VAM do much better with organic farming,” Carter says.

Carter continues to promote the benefits of organic farming techniques for crops that rely on mycorrhiza to access nutrients in the soils, but truffles are now his main area of research. His family owns a truffle nursery in outer Melbourne’s Dandenong Ranges, selling infected seedlings and providing advice to potential truffle farmers.

An International Specialised Skills Institute grant allowed Carter and his son (who is also studying truffles as part of his agricultural science qualifications) to travel to Italy, France and Spain and study the truffle’s ancient home. “We were taken right back to the foundations of the industry. At times we could hardly believe that we were right at the heart of the truffle world – something we are striving to emulate in Australia,” says Carter.

One of the things Carter noticed was that the truffles seem to grow best in what he calls “hungry” soils at the base of trees that “never look luxuriant”. Only through scientific explanations of puzzles like this will the collapse in global truffle production be reversed.