Edible Fungi Trials

There is potential for New Zealand to supply the Northern Hemisphere gourmet market with out-of-season edible fungi such as truffles and mushrooms. Plant & Food Research has an ongoing programme aimed at identifying which species can be grown here and how crops can be successfully established. Black truffles, Italian white truffles and saffron milk cap mushrooms are just three of the most promising species but they are all tricky to grow and just what triggers them to establish well and begin to fruit is not well understood.

Plant & Food Research (formerly Crop & Food Research) has for some time had a programme aimed at developing an industry exporting high-value edible mycorrhizal fungi (EMF) to Northern Hemisphere markets out-of-season. Mycorrhizal fungi that grow on most plant roots share a symbiotic relationship with their hosts. While the plants benefit from access to minerals in the soil, they provide a place for the fungi to live and a source of energy for them.

Some of these fungi produce truffles and edible mushrooms including some of the worlds most expensive foods. Prigord black truffles are possibly the best known and the most sought after.

Together these truffles and mushrooms have an international market worth billions of dollars. Most are collected from the wild mainly in the Northern Hemisphere autumn or winter and are best eaten fresh, so out-of-season there are no fresh truffles or mushrooms and chefs have to use very inferior, preserved material.

Crop & Food Research began in the 1980s to develop systems for inoculating plants with specific mycorrhizal fungi and the first Prigord black truffles were harvested in 1993 five years after planting at a truffire, near Gisborne.

Today Plant & Food Research (PFR) has laboratory techniques for inoculating plants with:

Prigord black truffle (Tuber melanosporum)

Bianchetto white truffle (Tuber borchii)

shoro (Rhizopogon rubescens)

saffron milk cap (Lactarius deliciosus)

porcini (Boletus edulis)

matsutake (Tricholoma matsutake)

burgundy truffle (Tuber uncinatum).

PFR is also exploring the potential of high value, gourmet fungi species new to New Zealand.

PFR pioneered and led the establishment of truffires all around the country, ranging in size from 20 trees to over 4000 trees. However, since 2007, PFR stopped the commercial production of truffle trees to focus on research. The role was taken over by a few private companies (Oakland Truffire, Canterbury Truffles, Strong Trees, Southern Cross Truffles Ltd.). Oaks and hazels are recommended for black truffles because hazels may produce earlier and oaks may produce for longer. Truffles prefer areas with warmer summers and cooler winters, and require alkaline soils(above pH 7.5 with an optimum of 7.9 for the Prigord black truffle) that are be well-aerated and well-drained, rich in calcium carbonate and with a carbon-nitrogen ratio of about 10:1. The presence of other trees that may have competing mycorrhizal fungi on their roots may also hamper production.

The results of inoculation with several mycorrhizal fungal species (truffles, saffron milk cap, shoro) are in most cases extremely good as long as care is taken to ensure good quality inoculum and appropriate substrate conditions. However, it is still challenging nowadays to maintain the same quality while producing a very high number of plants. The quality control of the trees produced is crucial but unfortunately not developed enough today due to high testing costs. After planting, again the situation varies with fungal species but the reasons why fruiting may not happen or may be inconsistent (with the Prigord black truffle for example) are not well understood yet. For all species it happens in nature why not through laboratory inoculation?

Two inoculation methods are used mycelial (vegetative) and spore inoculation. In theory spore inoculation is the most convenient and the cheapest way to establish mycorrhizae on large numbers of trees and is the recognised technique for some truffle species. However, the majority of EMF species have specialised germination triggering systems that are poorly understood. Their spores are dormant or relatively short-lived and the role of spores in the natural spread of many EMF is still under debate. There is some evidence suggesting that late-stage EMF (those that fruit on mature trees only) slowly expand and establish mycorrhizae through existing mycelial structures and only occasionally disperse through spores.

Alexis Guerrin, Team Leader of Edible Mysorrhizal Fungi at Plant & Food Research, believes that the potential for the industry is excellent. For black truffles, the main crop is the truffle itself and it is very valuable, so the value of the trees is small by comparison.

For other fungi like saffron milk cap they are a secondary product under a timber plantation, but because they fruit every year they provide a valuable income stream. All are symbiotic fungi that often help trees to grow. In some cases they may be demanding on the tree but they are not a disease and even if they do restrict growth they still confer drought or disease resistance to the trees, a crucial benefit at planting.

The procedure is that foresters plant mycorrhized seedlings. In the case of the saffron milk cap mushroom NZ has the biggest plantings worldwide. Porcini and saffron milk cap are soil tolerant species, so many NZ soils are suitable as long as they are reasonably free-draining. However, some truffles require high pH soil that is also free-draining and friable. Some truffle and mushroom species can be demanding in terms of tree species while others have a broad host range (porcini for example).

Saffron milk cap is the most commercially advanced mushroom species so far and some will soon be exported, but Alexis says that it is still unknown how to manage the crop so yield can be optimised and so we know how long the production can be maintained in the longer term. Also there are post-harvest issues to resolve mushrooms are fragile.

Obviously there would be great advantages in being able to establish new edible fungi under pines, and PFR research is working on aspects of this. One of the problems is being able to determine what species of fungi are present, and they have developed molecular tools for that purpose. They are currently looking at ways of establishing a new species that has ERMA approval to be grown under containment, and at factors that affect the persistence and development of several important species after planting eg. competition from other fungi, how well the mycorrhizae develop on seedlings, the impact of irrigation etc.

PFR has also had some success at establishing the Japanese fungus shoro in a pine plantation at Lincoln. A fruiting body was found in 2009 under a P. radiata tree that was out-planted in the field late 2007. There is also a New Zealand shoros, and PFR has established that it is genetically different from the Japanese variety and probably came from the USA with the introduction of Pinus radiata Using morphological and molecular diagnostic techniques they were able to confirm this as the first fruiting of Japanese shoro cultivated on P. radiata in the Southern Hemisphere.

Jeff Waeston, owner of Harakeke Truffire, planted his truffire in 2002 because the idea of edible fungi appealed. The older trees are common oaks and hazel nuts, and more recently he has planted Pinus pinea (stone pine). The strategy is to have a variety of tree species in case some tree-based issue develops.

The main target species is Bianchetto (Tuber borchii), the Italian white truffle, chosen because it was a new opportunity, had potentially high value and was well suited to lifestyle block-scale horticulture. It was also a less risky investment option than black truffle because it is a more aggressive fungus and more likely to compete successfully with any fungi already growing on other trees nearby and beyond the property boundaries. Contaminating fungi eventually finding their way into and fruiting within the truffire are inevitable as their spores are wind-borne. Also, because Bianchetto has a wider ecological range than black truffle it was expected to be more tolerant of the slightly cooler Christchurch temperatures.

It took a little over 5 years from planting/inoculation to production of the first commercial crop of Bianchetto in the Southern Hemisphere in 2008. That was encouraging, but last years crop was disappointing although it was the same for all growers and the reason is unclear. This year production has started, says Jeff, but there have been few mature truffles so far because of the late arrival of winter temperatures.

We havent been willing to search too hard because once truffles are disturbed they have to be harvested and the immature truffle doesnt have as much value, he says.

We have had many export inquiries but currently we are selling to a small number of domestic restaurants and hotels. The domestic market is very keen on getting truffles but we dont know how big the market is or how many other growers are getting to the point where they are producing. Having more will be good for industry because it will help ensure continuity of supply to the market.

There are probably around 20 white truffle growers at present. The main fruiting months seem to be May to July, although Jeff is unsure because this is only their third season.

Jeff uses a dog he trained himself to sniff out truffles. He says that the dog needs to have a natural prey drive. His is a short-haired German pointer found for him by an animal behaviourist who also helped train the dog using a reward system hiding truffle scented baits and making a game of it.

I never cease to be amazed by his ability to find a truffle weighing less than a gram, he says.

The smallest one he found was just 0.1g and the size of a match head.