Possible antibiosis effect of the metabolites of three fungal species resident in rice straw and husk compost on the in vitro radial and vegetative growth by Pleurotus ostreatus strain EM-1and P. eous strain P-31

Abstract

The inhibition of one microorganism by another through chemical means (antibiosis) or by competition for nutrient in a micro-ecological environment is a well-known phenomenon in mushroom composts during preparation of substrate for bioconversion into fruiting bodies. The effect of culture metabolites of three resident fungi (Aspergillus flavus, Penicillium citrinum and Trichoderma harzianum) in rice straw and husk on growth of mycelium of Pleurotus ostreatus and P. eous was studied in vitro using the radial growth and dry weight accumulation method in solid and liquid media respectively. Estimation of radial growth and dry weight of the mycelium was carried out in Potato Dextrose medium amended with 1:1 - 1:10v/v dilutions of the cultural filtrates. The antibiosis test showed that the cultural filtrates of the three respective test fungi variably depressed radial and vegetative growth of P. ostreatus and P. eous on agar and liquid medium respectively. The antibiosis effect was severer on P. ostreatus than P. eous. T. harzianum culture metabolite was the most potent completely preventing radial growth of both oyster mushrooms at all concentrations tested (1:1 -1:10v/v). The antibiosis effect of the metabolites of the test fungi on growth of P. ostreatus and P. eous can be ranked as follows (in decreasing order)T. harzianum>A. flavus>P. citrinum. The estimation of dry matter accumulation by the oyster mushrooms in the presence of the culture metabolites gave the same trend except that increasing dilution of the cultural filtrates permitted feeble growth of the mycelium of both Pleurotus species but never approximated the dry weight obtained in the control. The highest concentration of culture filtrates of the three test fungi (1:1v/v dilution) depressed vegetative growth by 5-6 times. Thus the test fungi A. flavus, P. citrinum and particularly T. harzianum may adversely affect economic productivity of the mushrooms if found in high population in the compost. The practical implications of the findings are discussed