Characterization and domestication of indigenous Pleurotus mushroom species in Kenya

Abstract

Mushrooms are traditionally consumed In Western, Nyanza and Coast regions In Kenya. They have been utilized by local communities for a long time and form an integral part of a long standing cultural and traditional practice. However, collection of wild mushrooms has been decreasing with time due to changes in agricultural practices and degradation of indigenous forests. Until now, there has been no report on the diversity, distribution and abundance of indigenous Pleurotus mushrooms in Kenya. On the other hand, mushroom growers in Kenya are constantly searching for new strains of Pleurotus mushroom. The strain with a high ability to colonize substrate and fruit quickly is the most preferred. Currently all cultures of mushrooms multiplied in Kenya are imported from Belgium, China, France, Japan and South Africa. This study was formulated to characterize and develop protocols to domesticate indigenous Pleurotus mushrooms. The project sought to determine the diversity, distribution and abundance of indigenous species of Pleurotus mushrooms from the Kakamega and Arabuko Sokoke forests, their cultivation requirements and nutritional composition. Data on Pleurotus diversity and distribution patterns was obtained by opportunistic sampling. The samples were characterized and identified using morphological and molecular markers. Their growth and yield performance on selected locally available substrates was determined and the elite species selected for domestication studies based on their ability to develop basidiomata under the experimental conditions. Elite species of Pleurotus mushroom-was analyzed to determine its proximate composition, mineral, amino acid and vitamin contents. Crude protein, crude fat, moisture content, dry matter, ash, crude fiber, and carbohydrate content and amino acids were determined according to the Association of Official Analytical Chemists (AOAC, 1995 and 2006) methods. Mineral element analyses were determined using flame technique of Atomic Absorption Spectrophotometer (Model-Shimadzu AA-6300). Phosphorus content was estimated by Ultra Violet spectrophotometer (Model: Spectrophotometer) Ammonium molybdovanadate method (AOAC, 2006). Vitamins were determined using the methods described by British standards and AOAC official methods of Analysis and protein through the Kjeldahl method. The calorific value was determined using a calibrated Adiabatic Bomb Calorimeter (Ika-Kalorimeter C400 Adiabatic) under controlled conditions. The collections were grouped under five species. Four Pleurotus species were collected from Kakamega forest while one from Arabuko Sokoke forest. Combination of morphological and genetic markers revealed the diversity in the Pleurotus isolates. Pleurotus citrinopileatus mushroom was the most abundant and widely distributed species in Kakamega forest. The occurrence of Pleurotus citrinopileatus on new hosts was reported for the first time in Kenya. Only one isolate, Pleurotus citrinopileatus developed fruiting bodies under experimental conditions and was considered for production and nutritional analysis experiments. Bean straw emerged as the most suitable substrate for cultivation of this mushroom. Bean straw showed the shortest colonization period and the highest biological efficiencies and yields with maximum yield (397.71 g/kg wet substrate) and biological efficiency of 148%. Proximate analysis of P. citrinopileatus revealed that it contained 22.10% protein, 1.32% crude fat and 20.78% fibre. The mushroom was also fourid to contain minerals in variable amounts with the most predominant being Potassium (2.28%). Eight essential amino acids were detected namely Leucine, Valine, Threonine, Lysine, Phenylalanine, Isoleucine, Methionine, and Tryptophan. Leucine was the most abundant. Glutamic acid though non- essential was present in high proportion (3.07%). Vitamin 83 (Nicotinic acid) was the most abundant vitamin. Tropical rain forest conditions in Kakamega favored Pleurotus mushrooms occurrence and diversity more than the coastal dry forest. This study recommends bean straw as a new substrate for cultivation of Pleurotus citrinopileatus which is an excellent source of protein and micro-nutrients. Key words: Diversity, cultivation, nutrients, forest, hosts