Antagonistic activity of bacteria and fungi from horticultural compost against Fusarium oxysporum f. sp. melonis

The use of composts to suppress soil-borne plant pathogens has been extensively reviewed in recent decades, and several micro-organisms have been identified as biocontrol agents in compost-amended substrates. The aim of this study was to investigate the in vitro and in vivo inhibition and suppression of antagonistic bacteria and fungi from several compost classes toward Fusarium oxysporum f. sp. melonis (FOM). This fungus causes Fusarium wilt of melon which is considered a critical problem in most melon crop zones where it results in extensive economic losses. In addition, effects of the raw material, aeration conditions during composting process and compost maturity on the isolation of biocontrol agents were also analysed. Microbial strains (493) were isolated from compost samples at different maturation phases (245 bacteria, 73 actinomycetes and 175 fungi). Initial soil dilution plate screening detected 179 isolates inhibiting FOM growth. Cell-free extracts of the 179 selected strains were prepared, concentrated and then assayed for their effects on FOM growth from which 10 fungi were antagonistic. The effect of selected fungi on Fusarium wilt of melon was assayed under greenhouse conditions. Results showed that optimal aeration during the composting process was favourable for the isolation of biocontrol agents. Strains with the highest biological control activity were isolated from mature compost samples and were mostly identified as Aspergillus spp. These were consequently considered as potential biocontrol agents against FOM.