Optimizing culture conditions for the antagonistic activities of Trichoderma viride against Sclerotium rolfsii causative agent of southern blight disease of tomato

Aims: Sclerotium rolfsii is a pathogen of agricultural crops such as tomatoes. Trichoderma viride has been shown to control this pathogen effectively but the optimum conditions of this biocontrol agent need to be determined. This piece of research was therefore aimed at studying the conditions that could be maintained in maximizing the full potential of T. viride. Methodology and results: Malt extract agar was separately supplemented with different carbon sources (glucose, sucrose, maltose, lactose, and mannitol), nitrogen sources (peptone, ammonium nitrate, zinc nitrate and sodium nitrate) as well as salts (NaCl, CaCl2, KI, BaCl2) at different concentrations. Effect of different temperature and pH ranges was also evaluated. All the carbon used supported the growth of both S. rolfsii and T. viride at all concentrations. The growth of S. rolfsii was less than 90 mm at 3% of all the carbon used compared to the plates in which no carbon sources were added whereas the growth of T. viride was 90 mm. There were morphological changes in the growth of both T. viride and S. rolfsii with increase in concentrations of peptone and ammonium nitrate. The greenish colour of T. viride was completely lost while S. rolfsii became fluffier. For peptone, the percentage reduction ranged from 68.52 to 63.33 while for zinc nitrate and sodium nitrate, the percentage reduction ranged from 85.19 to 80.74 and 55.00 to 43.70 respectively. Also, there was increase in antagonistic property of T. viride with the inclusion of salts (NaCl, CaCl2 and KI) at all concentrations used. However, barium chloride was toxic to T. viride at 2-5% (w/v). The optimum temperature and pH for the antagonistic property of T. viride appeared to be 37 degrees C and 6.0 respectively. Conclusion, significance and impact of study: Inclusion of different carbon, nitrogen and salts increased the antagonistic activities of T. viride against S. rolfsii although lactose appeared to be the best carbon source while zinc nitrate and CaCl2 were the best nitrogen and salt respectively. Barium chloride was toxic to T. viride at 2-5% (w/v).