Truffles, mushrooms and mycorrhizas
© Truffles and Mushrooms (Consulting) Ltd                     
Edible mycorrhizal mushrooms
Most mushrooms that we encounter in our local supermarket or delicatessen, like the button mushroom, are grown on dead plant material.  However, more than 1000 species of edible mushrooms such as the truffles (below left), chanterelles (top right) and porcini (below right) are formed by ectomycorrhizal fungi and some of these have well established worldwide markets measured in billions of dollars.  
Most of these ectomycorrhizal mushrooms are not found south of the equator and only fruit for short periods during the year.  There is, therefore, a golden opportunity to introduce these species to the Southern Hemisphere and produce them for out-of-season Northern Hemisphere markets - an idea that was first floated in New Zealand in the late 1970s.

There has been a marked decline in the harvests of some edible mycorrhizal mushrooms over the past century which is illustrated by the official figures for the Périgord black truffle (Tuber melanosporum) harvests in France.  This makes the production of edible mycorrhizal mushrooms in the Southern Hemisphere all the more attractive.

Click for “A list of putative edible or medicinal ectomycorrhizal mushrooms” ectomycorrhizal mushrooms.
Combined French Périgord black truffle and winter truffle production (tonnes)  1903 - 2001 (from Michel Courvoisier).

Possible reasons for this decline include deforestation, the loss of host plants within forests due to pests or disease, changed forest management practices such as planting more densely than occurs in natural forests, the replacement of natural forests with plantations of species that are poor hosts for edible mycorrhizal mushrooms, global warming since the last ice age, soil compaction by hordes of pickers, acid rain and, for truffles, the loss of expertise during two World Wars as to where and how to find them.