Optimization of King Oyster Mushroom (Pleurotus eryngii) Substrate Using Lignocellulosic Affordable Wastes

King oyster mushroom (Pleurotus eryngii) belongs to Basidiomycota division, Agaricomycetes class and Pleurotaceae family. This mushroom generally grows on wood wastes of Apiaceae family. The Pleurotus eryngii is found in pastures, meadows, gardens and seldom in grassy forest clearings and hilly areas. The Pleurotus of the Umbellifers occupy an area in the Northern hemisphere between the 30 and 50º N. These species are mainly found in the subtropical regions of the Mediterranean, Central Europe, Russia, Ukraine, Central Asia and Iran. The P. eryngii sensulato is the only taxon within the genus, which grows in association with plants. P. eryngii has distinguishable characteristics such as coherent texture, unique form, favorable taste and high durability. Mushroom cultivation represents the only current economically viable biotechnology process for the conversion of waste plant residues from forests and agriculture. The species of these genera show much diversity in their adaptation the varying agro-climatic condition which makes more cultivated species than other mushrooms. Special ability of Pleurotus family is growing in lingocellulosic plant or agricultural wastes without needing to prepared compost and casing soil. Pleurotus is an efficient lignin- degrading mushroom and can grow and yield well on different types of lignocellulolosic materials. Type of substrates for mushroom growing depends on available plant or agricultural wastes. In Europe, wheat straw is used for mushroom growing; whereas in Asian South-East countries sawdust is more popular. Different materials for cultivating of P. eryngii have been suggested in different regions of the world; but a few studies have been done on suitability of various lignocellulosic affordable wastes for P. eryngii production in Iran. Therefore, the current study aims to evaluate effects of various locally available agro wastes on the growth characteristics of King oyster mushroom (P. eryngii).
Sawdust was utilized as the main substrate obtained from beech and populous trees (1:1). After being rinsed off in water and supplemented with calcium sulfate (3%) and calcium carbonate (3%), the substrate was filled in 20 × 40 cm polyethylene bags weighted to 800 grams. Sterilization was performed at 121 °C under pressure of 1.5 bars for two hours. A cultivated P. eryngii strain was then inoculated in the cooled material at a rate of 3% of dry/fresh substrate. The experiments were conducted based on a completely randomized design with five treatments and four replications, measuring mycelial growth (MG), number of fruiting bodies (NFB), mushroom weight, and biological efficiency (BE). AMG was measured in both test tubes and in petri plates in different pH levels (5.5, 7, and 8.5). Data were analyzed by JAMP 4.0, while graphs were drawn by Microsoft Excel 2007 and SigmaPlot 12.0 software.
The pH of 7 was found to be the best for obtaining maximal MG under all treatments after seven days. The highest amount of MG was obtained with substrate No. 1, while the least was observed in the culture of substrate No. 5. The substrates No. 1 and No. 5 generated the highest and lowest NFBs (p≤0.05). However, there was no significant difference (p≥0.05) in NFB between substrates No. 1 and 3 or between substrates No. 2, 4 and 5. The BE percentages obtained from experimental treatments No. 1, 2, 3, 4, and 5 were 64.81, 49.74, 59.22, 28.72, and 19.8, respectively. The comparison of means of different growth characteristics revealed that there was no significant difference between substrates No. 1 and 3 or between substrates No. 4 and 5 (p≥0.05).
In this time, only two species (Agaricus bisporus and P. ostreatus) are producing in Iran, whereas at least 10 species of edible mushrooms are cultivating in the world. King oyster mushroom has low cost of production and distinguishable characteristics. Therefore, this mushroom can be use as alternative for button mushroom (A. bisporus). Many kind of agricultural wastes are in use for mushroom cultivation. Understanding the effects of substrate materials on mushroom production will be very valuable. The average number of fruits and biological efficiency of treatment No.1 showed significant difference with other treatments. Hence, the treatment No. 1 could be used for commercial production of King oyster mushrooms in Iran. Growth rate of P. eryngii was very diverse, in respect to the determinate values of the environmental factors. On the basis of the average growth rate of the strains, we could conclude what are the optimum ecological values of the species, though these conclusions did not always coincide with the optimum values of the certain strains. However, more research needs to be done to obtain regular and homogeneous supply of this mushroom.