The experiment was carried out at the Biochemistry Laboratory and Mushroom Culture House (MCH) of the Department of Biochemistry of Sher-e-Bangla Agricultural University, Dhaka, Bangladesh. Pleurotus mycelia colonized packets, weighing 500 g each, obtained from Namdec, were used. The cultivation substrate consisted of wheat bran' supplemented sawdust in a polypropylene bag sealed with cotton wool and sterilized at 121°C for 20 min. Mycelia culture of the four newly-introduced oyster mushroom strains, namely P. high-king (PHK), P. ostreatus (PO3), P. geesteranus (PG1), P. geesteranus (PG2), and P. ostreatus (PO2), was inoculated separately. Pleurotus ostreatus (PO2) was used as the control, since it is the most commercially cultivated edible strain in Bangladesh.
For each evaluated Pleurotus strain, three replicate bags were prepared and incubated at five different plots in the MCH, for full colonization of the substrate. Once fully colonized, induction of fruiting was done by cutting a "D" shape with a sterilized blade at the opposite end, in the upper position of the culture bags. The cut plastic sheet was then removed. The opened surface was scraped slightly to remove the thin, whitish mycelial layer. Then, the culture bags were soaked in water for 15 min and inverted to remove excess water for another 15 min. The packets of each mushroom species were placed separately, side?by?side, on the floor of the culture room and covered with newspaper. The moisture of the culture room was maintained at 80–85% relative humidity by spraying water three times per day. The room lighting was maintained at approximately 300–500 lx and ventilation was kept uniform. The temperature of the culture house was maintained between 22 and 25°C.
The number of primordia (pinhead' like appearance) was counted and recorded. Oyster mushrooms achieved maturity within two to three days after primordia initiation. The matured fruiting body was identified by the curve margin of the cap, as described by Amin et al. (2007b). Mushrooms were harvested by twisting to uproot from the base.
Fully developed fruiting bodies were counted to determine the number of effective ones; tiny and deformed fruiting bodies was discarded at the time of counting. To obtain the average weight of individual fruiting bodies, the weight of each flush was taken and divided by the number of fruiting bodies. Average length, breadth, and thickness of three randomly selected pili (cap) were measured (mm) using slide calipers. The length and diameter of the stipe were also measured (mm). Mean fresh weight of the three consequent flushes of each bag was calculated for total yield (g per 500 g per bag). Fruiting bodies were collected as cluster form from spawn bags. The whole cluster of fruiting bodies was considered for biological yield measurement, and the cleaned fruiting bodies (separated from cluster by removing lower tough and dirty portion) were weighted to obtain the economic yield (Sarker et al., 2007b). The conversion percentage (biological efficiency) was determined (Pathmashini et al., 2008) as follows: biological efficiency (BE) = (grams of fresh weight of mushroom/dry weight of substrate) × 100.
After harvesting the first flush, packets were scraped again in the position where the "D" shaped cut was made. The packets were soaked in a bucket for 15 min, inverted for another 15 min to remove excess water, and placed in the culture house. This practice was repeated after each flush. Water was sprayed regularly to maintain humidity (80–85%). Three flashes of each packet were harvested and recorded.
Fruiting bodies of all five oyster mushroom strains were analyzed for the nutritional composition according to the Association of Official Analytical Chemists (Cunnif, 1995). The contents of moisture, dry matter, protein, lipid, ash, carbohydrate, crude fiber, and minerals were determined. The evaluated minerals included nitrogen, calcium, magnesium, potassium, phosphorus, copper, zinc, manganese, and iron. Values for N were determined using the micro Kjeldahl apparatus; P values were calculated by a spectrophotometer; Ca, Mg, Cu, Mn, Fe, and Zn values were obtained using an atomic absorption spectrophotometer; and K values were determined by a flame photometer after standardizing against respective elements (Cuniff, 1995). The fractions (%) of protein, fat, crude fiber and ash were added together and subtracted from 100 to obtain the total carbohydrate percentage, whereas the dry weight of nitrogen and fat-free extract was calculated as the percentage of crude fiber.
The data were statistically analyzed using the MSTAT'C computer package program (Michigan State University, East Lansing, MI, USA). Analysis of variance was conducted and means were compared using the least significant difference (LSD) test, at 1 and 5% probability (Gomez & Gomez, 1984).