Mycoparasitic interaction is a basic indicator to assess the antagonistic properties of microorganisms (Rahman et al. 2009). There are several methods that can be used to assess this interaction and the most common one is the dual culture method. In this study, four mushroom isolates which have been identified as Cop. disseminates (12b), M. palmivorus (42b), T. maxima (56e) and L. sajor-caju (60a) show a various degree of inhibition toward test fungi based on the dual culture analysis. M. palmivorus gave the highest PIRG value compared to the other isolates. A similar observation was reported by Lallawmsanga et al. (2016), M. palmivorus, L. sajor-caju, and T. hirsute show antifungal activity towards Fusarium oxysporum, Candida albicans, and Fusarium proliferatum. Abdullah et al. (2005) also showed Malaysian tropical mushrooms such as Marasmiellus sp. and L. squarrosulus have the ability to produce secondary metabolites that have an antibacterial and antifungal effect.
One of the possible inhibition mechanisms exert by this mycoparasitic interaction are mycelium interaction. Different mycelium density and inhibition pattern on the agar plates were observed. Boddy (2016) reported mycelium interaction could be observed by naked eye including the growth rate of the mycelium, changes in mycelium morphology, pigmentation and the presence of lysis zones. Other mechanisms are through the ability of mushroom isolates to grow faster than the test fungi.
These mushroom isolates also suppress the growth of the test fungi through the production of various secondary metabolites including volatile and non-volatile metabolites. Based on the in vitro analysis, we able to observe the growth inhibition of test fungi when exposed to the volatile compounds produced by the mushroom isolates. However, none of the mushroom isolates had done above 45% PIMG value. This shows that their volatile compound does not give a strong inhibitory effect. Some volatile compounds were capable to suppress other fungal or microorganisms generally. Gary et al. (2001) identified five classes of volatile compounds such as esters, lipids, alcohols, acids and ketones. A volatile compound such as junipal from Daedalea juniperina has been reported to possessed fungistatic and fungicidal effects (Fries 1973). Furthermore, Osaki-Oka et al. (2019) identified Isovelleral, a volatile compound from fruiting bodies of Russula spp., able to inhibit mycelial growth and conidial germination of a phytopathogenic fungus, Alternaria brassicicola.
Mushroom isolates are also capable of producing a diffusible toxic substance which non-volatile. In general, microorganisms will generate waste products which also known as metabolites during the growing phase. Some of these metabolites have properties that can inhibit other microorganisms. In this study, L. sajor-caju shows highest PIMG value indicating that their non-volatile compound has inhibitory properties and B. panici-miliacei was effectively inhibited compared to another test fungus. A similar study was done on basidiomycete Earliella scabrosa that capable to produce active metabolites such as 2(3H)-furanone, 5-heptyldihydro-, 4H-pyran-4-one, 2,3-dihydro-3,5-dihydroxy-6-methyl- and triacetin to inhibit the growth of fungi on rubberwood (Peng and Mat Don, 2013). This finding also proves that basidiomycete has the ability to produce usable metabolites. Study on Trichoderma viride shows positive inhibition through the production of diffusible metabolites on Pythium sp. (Patil et al. 2012). Similar study on Trichoderma spp shows positive inhibition through production of antifungal non-volatile metabolites on soil borne diseases of chickpea (Nagamani et al. 2017). According to Naher et al. (2014), secondary metabolites can exist in the form of the volatile and non-volatile compound. 6-pentyl-alpha-pyrone (6PAP) is an example of a well-known volatile antifungal compound which has been characterised as a secondary metabolite (Siddiquee et al. 2009). Some of these volatile compounds are common to many fungi, and some are unique to certain species.
From all the tests performed, metabolites produced by mushroom isolates were effective inhibitors for the growth of B. panici-miliacei and Nigrospora sp. meanwhile, the opposite result was showed for C. lunata. This is because C. lunata is well adapted to the environmental changes and able to produce their own defence compound. A study by Jagtap and Suryawanshi (2015) used C. lunata as biocontrol agent candidate in controlling Fusarium oxysporum which causes basal rot of onion in their studies. In another study of Avinash et al. (2015) the crude extract of C. lunata showed antimicrobial activity towards bacteria and fungi.