Ecology and nutraceutical value of edible indigenous mushrooms. A case study of Kyebe Subcounty in Rakai District, Uganda

Abstract

The present study was conducted in two parishes of Kyebe Sub County in Rakai District located in the Lake Victoria Basin, Southwest of Uganda and West of Lake Victoria. The objectives of the study were: 1) to document the edible mushroom species; 2) to document indigenous knowledge and cultural practices on utilization of mushroom species; to assess the relationship between mushroom species occurrence, environmental factors and different vegetation types; 4) to assess the nutritional value of the common edible indigenous mushroom species; 5) to assess the antibacterial activity of edible indigenous mushroom species. Structural interviews were administered to 99 randomly selected respondents in a social demographic survey. Ten 1000m2 plots were established in each of three vegetation types (grasslands – 20 x 50 m, garden – 20 x 50 m and forest – 5 x 200 m) from where mushroom and tree species were assessed. Physical and chemical soil properties as well as canopy cover were determined in the sample plots. Sampled mushrooms were analyzed to determine nutritional content of food values (protein, carbohydrates, lipids and fibre contents) and antibacterial properties (qualitative and quantitative). A total of 4,077 individual mushrooms belonging to 5 genera and 10 species was recorded. Three individuals that could not be indentified were assigned to morpho species. 675 individual trees were also assessed belonging to 28 families, 43 genera and 46 species. Results show that mushroom species had food, medicine and cultural attachments to the local communities. Females knew more mushroom species than the males while the older reported more knowledge of mushroom species compared to the young. Podabrella microcarpa and Volvariella speciosa were used by the indigenous people for medicine and food. The number of mushroom species reported differed with respect to different categories of parish, marital status, education, occupation and time of residence in the area. Up to 85% of the respondents noted that environmental changes had affected the present availability of mushroom species while 94 % of them agreed that this brought about less mushroom species and the remaining 6% reported more mushroom species today. Mushroom species diversity and evenness were highest in the grasslands while dominance of mushroom species was highest in the forest. Pluteus sp was found occurring only in the grasslands, Agaricus sp2 and K/K/04/N1 were found in the garden while three species (Termitomyces sp1, P. microcarpa and Agaricus sp 1) were found in all vegetation types. Termitomyces sp 1 and pluteus sp were significantly correlated with some of the measured environmental factors. The environmental factors are pH, phosphorous and canopy cover for Termitomyces sp 1 and organic matter, potassium, sodium, sand and magnesium for Pluteus sp. Analysis of seven indigenous mushroom species showed no statistically significant difference in nutritional values (p=0.05). The indigenous mushroom species had generally higher amounts of carbohydrates than crude proteins, crude lipids or crude fibre. The antibacterial assay evaluated using mushroom methanol extracts against three strains of bacteria (Escherichia coli, Pseudomonas and Staphylococcus aureus). Four mushroom species showed activity against all the bacteria. At 500 mg/ml Pluteus sp was the only mushroom with diameter of inhibition zone (DIZ) above 12 mm on P. aeroginosa. The lowest Microbial inhibitory Concentration (MIC) of 15.625 mg/ml was in V. speciosa. Termitomyces sp 1 showed no activity in the wet extract but the sun dried extract showed activity against Pseudomonas aeroginosa and staphylococcus aureus. Podabrella microcarpa wet extract showed activity against all the test bacteria. On the other hand the sun dried extract showed activity on Pseudomonas aeroginosa only. The most susceptible bacteria was P. aeroginosa while the most resistant bacteria was E. coli. In conclusion, indigenous edible mushrooms are an important aspect of culture and ecology, while they have a potential antibacterial capacity that requires to be further explored. The integrity of the grasslands should be protected to promote mushroom conservation and Pluteus sp. should be the focus of further research in antibacterial characterization. Field studies on mushroom species in this area in the future should target the rain season between September and December. For any activity related to domestication, three species of mushrooms (Pluteus sp, Podabrella microcarpa and Volvariella speciosa) are recommended as candidates of focus because of their inherent characteristics.