A Thesis submitted in partial fullfillment of requirements for conferment of the degree of doctor of philosophy in agricultural science in the Meru University of Science and Technology.

References and Appendices

Phytophthora infestans belongs to Kingdom Chromista and is the causal agent of late blight in
tomatoes while Alternaria solani is a fungal pathogen causing early blight in tomatoes. Blight is
controlled using chemicals leading to safety challenges. Trichoderma is a soil borne fungi which
has been shown to have broad-spectrum antimicrobial activity and is used as a biocontrol agent.
Warburgia ugandensis is an indigenous tree of East and South Africa whose extracts have been
found to have antimicrobial properties especially in the medical field. The main objective of this
research was to evaluate the effectiveness of Warburgia ugandensis in the control of blight
pathogens affecting tomatoes and also the effectiveness of the synergy from Trichoderma
asperellum in controlling blight pathogens. The blight pathogens were isolated from infected
tomatoes in Nchiru, Meru County. Warburgia stem bark sample were processed to obtain crude
extracts using different organic solvents in multiple extraction method. Lyophilization was also
carried out to obtain crude extracts using water. Phytochemical analysis was carried out on the
extracts and minimum inhibitory concentration (MIC) was determined. Screening of the extracts
and Trichoderma for antimicrobial properties was carried out and the zones of inhibition were
observed and recorded. In vivo studies were carried out in the screen house using lyophilized crude
extract and the disease incidence observed and recorded. Percentage severity index and disease
reduction were calculated. Gradient column chromatography was carried out on the organic crude
extract and the fractions with similar thin layer profiles were pooled together before being
subjected to gas chromatography interfaced with mass spectrometry (GC-MS), from which the
profiles of the compounds in the extracts were determined. The quantitative data collected and
recorded was analyzed using ANOVA by Statistical Analysis Software (SAS) s and the means
separated using Tukey's tests. All statistical results with P<0.05 were considered to be statistically
significant. Warburgia ugandensis hexane crude extract had the highest mean inhibition zone in
A. solani while methanol crude extract gave the highest mean inhibition zone against P. infestans.
The MIC for A. solani was 1.25mg/ml while for P. infestans was 2.5mg/ml with Warburgia stem
bark lyophilized crude extract. Results of in vivo studies trial 2, showed least disease severity in
the combined treatment with Warburgia and Trichoderma at 27.81% for P. infestans and A. solani.
This was closely comparable with the commercial fungicide which had disease severity of 33.21%.
Warburgia stem bark was found to have different compounds which include terpenes,
sesquiterpenoids, fatty acids derivatives, and phytosterols among others. The results from this
research showed that Warburgia extracts and Trichoderma were effective in the control of blight
pathogens. Further investigation can be carried out on effects of specific Warburgia
phytochemicals in the control of blight pathogens and other phytopathogens.