The cultivation of edible mushrooms such as Pleurotus ostreatus commonly known as oyster mushroom has been undertaken by both commercial and cottage industry entrepreneurs in Ghana with appreciable success. However, the presence of competitors and potential pathogens in the substrate militate against increased yield and quality of fruiting bodies. The most prevalent pathogen Trichoderma harzianum in the compost for cultivating P. ostreatus is responsible for the green mould disease. In this study, in vitro pathological effects of spiking Triplochiton scleroxylon sawdust substrate with T. harzianum on pinhead emergence, percentage formation of fruiting bodies, weight of fruit body, yield, Biological Efficiency as well as morphometric data of stipe length, stipe diameter, cap diameter as criteria for reduced growth performance of P. ostreatus were investigated. The effect of the pathogen on the nutritional and elemental composition of the oyster mushroom were determined with the view of assessing the quantitative changes of nutritional and elemental composition of the mushroom using standard methods. Growth substrates inoculated with T. harzianum reduced pinhead formation; number of fruiting bodies formed, percentage conversion of pinheads, weight of fruiting bodies, and reduced morphometric measurements of stipe length, stipe diameter, cap diameter with all three flushes of the mushroom. Total yield of fruiting bodies in all three flushes in the T. harzianum-inoculated bags decreased by 67.4%, 68.5% and 83.3% respectively with the concomitant reduction of total yield by 52.3% and Biological Efficiency by 52.8%. Some of the control bags (uninoculated bags) also performed poorly as a result of contamination by T. harzianum, indicative of inadequate sterilization. Fruiting bodies of P. ostreatus grown in uninoculated compost contained Ca, Cu, Fe, K, Mg, Na, P, and Zn in contrast with the absence of Na, and Zn in the infected bags. There was a reduction in fat, crude fibre, crude protein, and carbohydrates of the fruiting bodies grown in the contaminated bags. On the other hand, total ash content was doubled in the carpophore from the T. harzianum spiked contaminated bags. The pathogen therefore has adverse effect on the production and marketing quality as well as the nutritional value of the fruiting bodies.
Keywords: Trichoderma harzianum, Pleurotus ostreatus, Fruiting bodies, Nutritional and Elemental Composition; Total Yield, Biological Efficiency, Morphometric Measurement.