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Friday, 25 July 2014

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Effect of substrate disinfection on the biological efficiency of Pleurotus sajor-caju (Fr.) Singer

Pleurotus sajor-caju, an edible mushroom belonging to order Agaricales of class Basidiomycetes is most promising mushroom, coming next to button mushroom in respect of its production at global level sharing 25 per cent of total world production. Although, it is not valid oyster species (Guzmán, 2000), even then it is as nutritious as other valid taxa which makes it an ideal food for human consumption.  In India, it is admired especially due to its excellent flavour, taste and above all, easy method of growing without any sophisticated infrastructure. For the growing of Pleurotus spp. paddy straw is found most common and efficient substrate (Ram, 1995; Dubey, 1999; Gupta et.al., 1999; Siddhant et. al., 2009) which is accompanying indigenous micro flora. The antagonistic interaction between these micro flora and desired fungus contributed the low productivity of mushroom (Bhandari and Singh, 1983; Sharma and Jandaik, 1980, 1981a, b and 1982; Shiddique et.al., 2004). Therefore, proper substrate disinfection is pre-requisite to eliminate weed and obtained good yield. It can be achieved by various methods (Arya and Arya, 2003; Bahukhandi, 1990; Champawat and Chitale, 2003; Kumar et. al., 1990; Ram and Thakur, 2005; Tewari and Pandey,1988).

In present communication, six months stored paddy straw was used for the cultivation of Pleurotus sajor-caju to evaluate the effect of following substrate preparation methods on the biological efficiency of this mushroom species.
1) Autoclaving (T1): This method included sterilization of substrate at 15 lbs pressure for 60 minutes (Tewari and Panday, 1988).
2) Hot water application (T2): In this method, paddy straw was boiled in the water for one hour at 100°C (Diana et. al., 2006).
3) Radiation treatment (T3): In this treatment, the straw substrate was exposed to U.V. light for 1 hour 30 minutes (Ram and Thakur, 2005).
4) Chemical treatment (T4): Paddy straw substrate was pasteurized in the solution of Formaldehyde (500ppm) and Bavistin (75ppm) for 18 hours as suggested by Vijay and Sohi (1987).  
5) Water (T5): Substrate was not pasteurized at all and it was only soaked in water for 24 hours. 

     The substrate disinfected by employed techniques, viz., T1,T2,T3 and T4 showed quick spawn run, primordial initiation and fruit body maturation than control [T5] (Table). The crop of P. sajor-caju was harvested in three flushes where yield and biological efficiency ranged 10-360 g and 02-72%, respectively. All the substrate preparation methods showed highly significant yield and biological efficiency over control (unpasteurized sets). It was recorded the maximum in chemical pasteurization (360 g, 72%), followed by autoclaving (340 g, 68%), hot water treatment (335 g, 67%) and radiation treatments (305 g, 61%). The unpasteurized sets gave negligible result (10g, 2%) in aforesaid manifestations (Fig). Among the treatments, chemical pasteurization was found most significant. The hot water treatment and autoclaving was considered as second best treatment which was pat par to each other.

During the course of study, two fungal species belonging to Ascomycetes (Peziza sp.) and Basidiomycetes (Coprinus spp.) were encountered on the mushroom beds. The unpasteurized beds, used in triplicate were severely infected by Coprinus spp. and Peziza spp. (Plate) which resulted in great loss in mushroom yield. The bed contaminated with Peziza spp. could not produced even a single fruit body. The higher decomposition of substrate was also noticed in unpasteurized beds.
The results revealed that disinfection techniques played a crucial role in minimizing the loss of production and biological efficiency (Fig) this also protects the beds from competitors.

The disinfection methods reduce the natural micro flora of substrate and improve substrate colonization and yield of mushroom. Due to this reason, pasteurized substrates showed quick mycelial run and higher sporophore formation. In respect of yield performance, chemical treatment gave significant response. This was because of the fact that chemical treatment permitted a minimum number of bacterial population which favoured the growth and production of more cellulase by Pleurotus spp. and thereby increased the yield (Krishnamoorthy et. al., 1991). Production of this enzyme is directly proportional to the yield of Pleurotus in vitro (Kochuthresiamma et al., 1991; Nallathambi and Marimuthu, 1994). Besides this, bacterial population actively corrodes the surface of the substrate providing more suitable site for the colonization of fungus. Pleurotus spp. are also reported to utilize the nitrogen fixed by N- fixing bacteria present in the substrate. In addition, chemical treatments slightly modified the nature of substrate and favoured the growth of fungal mycelium. As compared to chemical treatment, autoclaving and Hot water treatments gave insignificant response. This was due to higher temperature which eliminated all the beneficial microorganisms present in the substrate (Bano et al., 1979). Unpasteurized beds gave highly insignificant result in respect of reduction in yield and biological efficiency than pasteurized ones. It is well known that stored straw is an easy source of contaminants which competes with mushroom mycelium for the available nutrients. The loss in yield was either due to depletion of food material from the substrate required for growing mushroom mycelia or through the production of toxic substances by the microorganisms (Atkins, 1949). Although, Doshi and Singh (1991) stated that toxic metabolites produced by microorganisms are very mild and has little inhibitory effect on growth of Pleurotus sajor-caju and whatever effect is seen was because of depletion of nutrients from the medium due to contaminants. The higher decomposition of substrate was also visible in unpasteurized beds. It might be the combined action of contaminating microflora and cultivated fungus. 
During the cultivation of Pleurotus sajor-caju two types of competitor were encountered on mushroom beds. This result was supported by the conclusions given by different workers which revealed the presence of weeds associated with oyster mushroom cultivation (Vijay and Sohi, 1987, Siddique et al., 2004). No or lesser appearance of competitors in pasteurized substrate revealed the efficiency of treatments. Chemical treatment was effective against fungal competitors which is agreement with the finding of Champawat and Chitale (2003) and Pervez et. al., (2009) who reported formaldehyde and bavistin combination as a best pasteurization practice. The effectiveness of hot water and autoclaving methods was due to the high temperature that kills the foreign inoculums from the substrate while ultraviolet light in the range from 200 to 300nm affects the growth of the competitors. Direct exposure of UV radiation is lethal to their DNA.(PDF Copy)

Cite this as: Siddhant, Swapanil Yadav, Rupali Mishra and Ruchira Singh,  (2014): Effect of substrate disinfection on the biological efficiency of Pleurotus sajor-caju (Fr.) Singer Plant Archives 14(1):205-209. 


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