In vitro ANTAGONISTIC ACTIONS OF HUMIC SUBSTANCE ON THE GROWTH OF Sclerotium rolfsii AND THE BIOCONTROL Trichoderma spp.

Abstract

The effect of humic substance, isolated from a composting substrate, was evaluated on the mycelial growth of two strains of Sclerotium rolfsii and the antagonistic Trichoderma sp. two strains of S. rolfsii treated with humic substances, one strain isolated from tomato stems and the other isolated from the roots of sugar beet. In general, any HS treatment significantly reduced the radial growth of the S. rolfsii mycelium in normal potato dextrose agar (PDA) medium enriched with humic acid compared to potato dextrose agar medium free from humic acid. However S. rolfsii which isolated from tomato stems showed resistance against the effect of humic acid after 4 and 9 days from inoculation due to the soil treatment many times with humic acid. Humic acid treatment was also able to alter the sclerotial production either by significantly reducing the number of viable germinating sclerotia or by almost increasing the number of sclerotia to double as a resistance mechanism towards the survival of S. rolfsii. Apparently, the extent of the inhibitory action was related to some chemical and functional properties of HS, such as the COOH group content and elemental composition. On the contrary the same HS treatment generally did not inhibit the growth of Trichoderma sp. This study showed no significant correlation between HS chemical properties and Trichoderma sp. However, it showed the inhibitory effect of Trichoderma sp. in presence of humic acid on two isolates of S. rolfsii with percentage of inhibitions 53.3 % and 94.4%.