Ten million mushroom farmers can’t be wrong. Can they?Siu Wai Chiu and David Moore

Department of Biology, The Chinese University of Hong Kong, Shatin, Hong Kong S.A.R., China, and School of Biological Sciences, University of Manchester, Manchester, U. K.

Conservation issue 2Traditional usage of natural wood logs has been pursued to the extent that as availability of mature trees has declined attention has turned to younger trees and other tree species. China now faces the problem that the rate of deforestation is much greater than the rate of reforestation! There are regulations about planting and prohibitions on felling young trees, but these are difficult to monitor, and ‘conservation awareness’ is low among mainland Chinese.

Our analysis of strains of Lentinula edodes which are used for spawn production for farms throughout mainland China revealed remarkable genetic homogeneity. This probably results from the concentrated artificial breeding work that has been done using a limited range of imported Japanese cultivars.

Wherever you go in China, you can find large amounts of dried shiang-gu on sale.

An outdoor shiang-gu farm using natural wood logs in Hubei Province, China.

Technology - and the profit motive - can help.The ‘artificial wood log’ is a way to relieve the problem of deforestation. Solid wastes like sawdust (from furniture and timber industries), cotton seed hulls (from agriculture), straw (from agriculture) can be recycled. In addition, strains which produce fruit bodies without opening the plastic bag can be selected. This may help lower the spread of the cultivar genome. As would disposal by sterilizing the plastic bag

cultures after mushroom harvesting.

Somehow we must raise awareness of the need for conservation.The concept of sustainable management is too novel for the mushroom farmers of a third world country. An essential step is to educate the public and introduce these ideas. Education is the key.

We thank The University Grants Committee of Hong Kong, the Croucher Foundation of Hong Kong, the Huazhong Agricultural University, Sen Yuan Spawn Company, the Leverhulme Trust, The Royal Society, The British Council and the British Mycological Society for grants which supported this research.

In Lentinula edodes basidiospores are the only means of dispersal. The standard practice of harvesting the cultivated crop close to maturity creates the problem of mass spread of spores from the farms. Since cultivated strains have such a narrow gene pool they could contaminate the wild germ-plasm. Such a manner of dispersal also creates the problem known as ‘strain degeneration' which is a decreased crop yield after the first one or two years of production in the wood log system. This ‘disease’ actually results from competition and recombination between the original cultivar used to inoculate the wood log and invading basidiospores from the local environment.

Conservation issue 1Wider use of wild strains in cultivation would lessen the problem of an introduced cultivar genome invading the natural germ-plasm.

Our sampling areas (= asterisks) cover approximately 1700 km North to South, 700 km East to West

Although a very narrow gene pool is used in cultivated strains, our survey of diversity of rDNA sequences indicates that China harbours the greatest germ-plasm resource of the shiang-gu mushroom Lentinula edodes. Thus, protection of the natural environment is still the best strategy for conserving the biodiversity of this natural resource.

References:Chiu, S. W., Ma, A. M., Lin, F. C. & Moore, D. (1996). Genetic homogeneity of cultivated strains of shiitake (Lentinula edodes) used in China as revealed by the polymerase chain reaction. Mycological Research 100, 1393-1399.Chiu, S. W., Wang, Z. M., Chiu, W. T., Lin, F. C. & Moore, D. (1999). An integrated study of individualism in Lentinula edodes in nature and its implication for cultivation strategy. Mycological Research 103, 651-660.

Commercial use of artificial logs in central China

Lentinula mushrooms fruited on an artificial log in the Department of Biology of the Chinese University of Hong Kong.