AbstractsBiology & Animal Science

The controlled environment of greenhouses, the high value of crops, and the limited number of registered fungicides offer a unique niche for the biological control of plant diseases. During the past ten years, over 80 biocontrol products have been marketed worldwide. A large percentage of these that have been developed in greenhouses could predominate over chemical pesticides in the same way that biological control of greenhouse insects predominated in the United Kingdom. A review of the literature was undertaken to obtain information on biocontrol agents with specific reference to Trichoderma and Gliocladium spp. Literature on the application, types of formulations, limitations in formulation, registration and commercialization of these biocontrol agents were obtained. Trichoderma harzianum Strain KMD has been used successfully as a biological control agent against several soil-borne plant pathogens. Biological control agents should possess several desirable characteristics, including, ease of preparation and application, stability during transport and storage, abundant production of viable propagules and good shelf-life. A strain of Trichoderma harzianum KMD with potential biocontrol activity was used to determine the effect of culture conditions on spore shelf-life. The influence of four growing media were investigated on the spore ultrastructure and shelf-life, using a basal salts medium with C:N ratios of 3 and 14, and pH's of 4.0 and 7.0. Mycelial development and sporulation were positively affected by acidic conditions (pH 4.0). The effect of these culture parameters on viability and shelf-life were evaluated by counting colony forming units (c.f.u) before and after seven days of storage at 75% relative humidity (rH): The effect of carbon concentration on spore viability after seven days of storage was also determined by increasing concentrations of glucose while a constant C:N ratio of 3 or 14 at pH 4.0 was maintained at a 75% rH. Increasing carbon concentration and C:N ratios increased spore production times. Spore viability was greatest when harvested from a medium with a C:N of 14 at pH 4.0 even when storage time was increased to 45 days and rH was reduced to 12%. Ultrastructural studies showed that spores had two cell wall layers, with the outer being more electron-dense than the inner layer. This layer is the spore's first defense against adverse conditions. Spores obtained from this medium were larger, germinated better and had a longer shelf-life than spores from C:N 3 medium, possibly because the two cell wall layers acted as a thicker barrier against adverse conditions. Increasing carbon concentration, while maintaining a constant C:N ratio of 3 or 14 at pH 4.0 slowed down spore production. Viability of spores were similar when introduced on media with variable carbon concentrations but fixed C:N ratios. The ultrastructural differences and shelf-life studies, confirmed empirical results from liquid fermentation studies, that the pH and C:N ratio of the medium upon which spores of T harzianum KMD…