Cultivation of exotic and local mushroom species for commercial production.

Abstract

The project was undertaken primarily to determine the potential of growing Stropharia rugoso-annulata and Volvariella volvacea at a commercial level under South African conditions. Termitomyces umkowaani, an indigenous mushroom, was also investigated. Mushroom culturing, spawn production and optimizing fruiting substrates were determined. The feasibility of commercial and subsistence production in KwaZulu-Natal was investigated. Of the seven strains of S. rugoso-annulata purchased from CBS (Baarn, the Netherlands) that were tested, Strain 289.85 was the most vigorous. The best agar medium for culturing of S. rugoso-annulata was potato dextrose agar (PDA) followed by malt extract agar (MEA) and vegetable juice agar (V8). Maximum growth of the mushroom mycelium occurred from Day 7 to Day 14, as expected. The best spawn substrate tested was sorghum, and the best fruiting substrates tested were banana leaves and maize stover. As S. rugoso-annulata is a white-rot fungus capable of degrading lignin, this result was expected. S. rugoso-annulata grows best on substrates with a low C:N ratio. Strain 1665 of V. volvacea was the best of the three strains obtained from CBS. The best culture medium for V. volvariella was PDA amended with 1 % straw. V8 agar alone supported poor growth. In trials for suitable spawn and fruiting substrates for V. volvacea, banana leaves supported the best mycelial growth. Mycelium grown on V8 amended with 1% maize stover showed the greatest expansion on the substrates tested. A strain of T. umkowaani was isolated from a fresh basidiocarp collected in Pietermaritzburg, KwaZulu-Natal. Growth of T. umkowaani was most rapid on a Basal Medium but mycelial vigour was inferior to that of mycelium grown on Basal Medium amended with rabbit faeces, especially at the level of 2.5%. High levels of contamination occurred when more rabbit faeces was added to the Basal Medium. Microbial contamination was a major limiting factor to the productivity of this project. The primary sources of culture contamination were due to mites, inadequate sterile technique and a high level of Trichoderma spores in the Department due to an ongoing Trichoderma biocontrol project. Placing the bags of cultures on trays with the edges smeared with petroleum jelly effectively kept the mites away from the cultures. The contamination of a stock culture with Penicillium was solved with the use of Benomyl-amended agar media. Contamination problems in spawn production were the result of the inoculation process (especially when conducted by one person), the initial leaking of cotton wool caps, polypropylene bag seams and micropores and cracks in the walls of polypropylene bags. Treating the cotton wool in the caps with Busan 30A prevented the entry of contaminant bacteria and fungi through the caps. The problem of leaking seams of the bags was solved by using a longer heating period on the bag-sealer machine. SEM studies confirmed the presence of micropores and stress fractures in the walls of the bags used in this project. This problem can be solved by using high quality polypropylene with a reduced content of plasticiser. A systems analysis of exotic mushroom production, the process of mushroom production, steps in the process, sales and constraints in the South African context, and possible solutions are discussed. Spawn production by small growers is not economically feasible due to the capital required. Access to capital is a constraint of production in controlled environments but should not limit outdoor production. However, outdoor production is constrained by climatic requirements of the fungi. Based on optimum temperatures, GIS maps of KwaZulu-Natal were generated to display the potential areas for outdoor production. Overlap of suitable regions for production of S. rugoso-annulata and V. volvacea is limited. Outdoor production of V. volvacea will be limited to Northern coastal regions for only four months of the year. A computerized decision support system was developed to answer questions of feasibility of production to the mushroom growers, based on the requirements of the mushrooms. A current lack of marketing of speciality mushrooms is considered to be a major constraint to sales and therefore potential production, particularly for subsistence farmers.