Comparative bioconversion of gamma irradiated and steam sterilized ‘wawa’ sawdust (Triplochiton scleroxylon L.) by mycelia of oyster mushrooms (Pleurotus ostreatus Jacq. Ex.Fr. Kummer)

Abstract

Pleurotus ostreatus was cultivated on composted ‘wawa’ (Triplochiton scleroxylon) sawdust subjected to physical pretreatment techniques of moist heat sterilization and gamma irradiation to assess their comparative mycelial growth performance. Substrates were moist heat sterilized at either 95-100oC for 2.5 hours or gamma irradiated with a Cobalt 60 source at 0 kGy, 5 kGy, 10 kGy, 15 kGy, 20 kGy, 24 kGy and 32 kGy at a dose rate of 1.7 kGy/hour using the ethanol chlorobenzene (ECB) dosimetry. Sorghum grains for spawns were also irradiated at same doses (0 kGy, 5 kGy, 10 kGy, 15 kGy, 20 kGy, 24 kGy and 32 kGy) and steamed similarly and their interactive mycelia growth effects on pretreated sawdust measured. Final linear growth, colonizing time, rate of growth, primordial emergence time, density and percentage contamination were monitored for the four weeks at 28-32oC. The fastest time taken for full colonization was 22 days by irradiated (I+I) samples of the 15 kGy set up while the fastest rate of growth of 28.3 mm/day was recorded by irradiated sorghum and steamed compost bag (I +S) of the 15 kGy set up. There was no significant difference (P>0.05) in final linear growth range of 190.2- 248.8 mm recorded for all pretreated samples which also recorded very low (0- 20%) contamination. Gamma irradiation was shown to be a good substitute and more efficient for sterilizing composted sawdust for mushroom cultivation and yield in the Ghanaian tropic conditions