SIRDC MUSHROOM PROJECT

Mushrooms constitute a very important vegetable relish, which is passionately enjoyed by many rural and urban communities in Africa. They are increasingly becoming a vital component of the human diet throughout the world. Mushrooms are rich in vitamins and protein that are essential ingredients in the human diet. Although mushroom protein content is less than that of protein from animal sources, mushroom protein contains all the essential amino acids required in human diet, including leucine and lysine which are often lacking in most of Africa’s staple cereal crops such as maize and sorghum.

Mushrooms and mushroom products have a great potential for supplying food for domestic consumption, as well as for export, provided international quality standards and timely supply schedules are maintained. The Industrial Development Corporation of Zimbabwe Limited (IDC) reports that the price of mushroom currently in South Africa is R29/kg. At this price, mushroom is contributing over R7 million per annum if all production is exported at that price. IDC also reports that the annual production of mushrooms in Zimbabwe is 250 tonnes while the demand for mushroom is 700 tonnes. This leaves an unmet demand of 450 tonnes. With the expanding tourism industry, the demand for fresh mushroom is likely to increase. Locally, the price of fresh mushrooms ranges from Z$40 000 to Z$50 000 per kg in the supermarkets. Since fresh wild mushrooms are seasonal, mushroom cultivation avails the product during the off-season periods.

Many African economies, including Zimbabwe’s, are largely agriculturally based. Maize, sorghum, millet and rice are grown and the grain is harvested. What is harvested from these crop plants is only 30% to 50% of their total biomass. The rest is left in the field. These crop residues are a good substrate for growing mushrooms. In fact, considering the huge tonnage of agricultural crop residues which is generated every year, and other categories of biomass, such as wild grass in the extensive savannas, sawdust and other forestry residues, Africa has the potential of becoming a major mushroom producer in the world. Additionally, the residue that is left after harvesting the mushrooms can be used as a protein-enriched livestock feed supplement. It can also be used as a very effective organic fertilizer and thus the cycle continues. The cultivation of edible saprophytic mushrooms does not take away farmland designated for other crops, so mushroom cultivation is compatible with the established small holder agricultural system in Zimbabwe. Furthermore, mushrooms can be grown all year round, hence small holder farmers can occupy themselves and become more productive by engaging in mushroom production during wintertime when agricultural activity is low and get additional income.

Successful cultivation of mushrooms and their commercial production in a beneficial and sustainable manner requires a series of appropriate technologies, including the development of pure culture spawn, good crop management and the appropriate training.

Spawn consists of a substrate that has been fully colonized by mushroom mycelia which is used as ‘seed’ in mushroom production. The quality of spawn in mushroom farming is very important. Poor spawn cannot produce a high yielding, high quality crop, even if all other steps in mushroom cultivation are carried out. Very few farmers are able to produce their own mushroom spawn because of the high costs involved in setting up and running the facilities.

Successful cultivation of mushrooms also depends on isolating a mushroom species from the natural world and growing it in an environment that gives the mushroom an advantage over competing organisms, such as other fungi and bacteria. Mushroom culture draws heavily on what happens in nature at the different growth stages. A mushroom house therefore has to closely simulate the ideal climatic requirements it terms of temperature, relative humidity, light and air exchange.

The Biotechnology Research Institute (BRI) of the Scientific and Industrial Research and Development Centre (SIRDC) produces and supplies high quality mushroom spawn to meet the ever-increasing demand of mushroom cultivation in Zimbabwe. BRI also provides the supporting services for mushroom growing, e.g. training and consultancy. At the moment, oyster mushroom spawn (Pleurotus sajor-caju and P. ostreatus) is being produced. Other mushroom types such as white button will be introduced in the near future.

Pleurotus is one of the choice edible mushrooms, which has gained great importance during the past decade. There are about 40 species described under this genus from different parts of the world. Pleurotus sajor-caju has been identified as one of the most promising mushroom species for cultivation in tropical and subtropical countries due to several reasons such as its rapid mycelial growth rate, high protein content (about 30 % protein on a dry weight basis), low calorie content, high content of unsaturated fatty acids and richness in vitamins. It is relatively easy to grow and can be harvested from 4 to 6 months after planting.

Adequate supply of mushroom spawn, it is hoped, will result in increased cultivation of mushroom. This in turn will contribute towards sustained food security, improved nutritional level of the families and increased family income through the sale of mushrooms by small-scale growers. Increased mushroom production will also contribute towards meeting the local consumption demands as well as exporting the surplus to regional and international markets to generate the much needed foreign currency.