| dc.description.abstract | Kenya is rated 6
in Africa with an annual overall production of 397,007 tons of tomato
fruit. Tomato production in Kenya is constrained by many biotic and abiotic factors and
among them, diseases such as early and late blight caused by Alternaria solani and
Phytophthora infestans, respectively. Farmers use synthetic chemicals to manage the
diseases. However, there has been major concern because they are costly, toxic to human
beings and the environment. Some of the products have been rejected in the international
markets because of high chemical residue levels. Some of the pesticides have not been
effective because of the pathogens undergoing genetic mutations that result to resistant
strains. This study sought to assess the genetic diversity of pathogens causing early and
late blight in tomato and their management using plant extracts and essential oils from
selected plants. Isolation of A. solani and P. infestans was done from infected tomato plant
samples collected from Mwea, for morphological and molecular characterization. Crude
extracts and essential oils of garlic, ginger, Mexican marigold and tick berry were tested
in-vitro to determine their efficacy against the two pathogens. Alternaria solani and P.
infestans were cultured in Potato Dextrose Agar and V8 agar respectively after amending
the media with different plant extracts and essential oils. Pathogen radial growth was
monitored per treatment over time. Tomato plants were grown in the greenhouse and
inoculated with spores of cultured isolates of A. solani and P. infestans. The inoculated
plants were sprayed with essential oils and ridomil
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synthetic fungicide as a control and
disease development was monitored. Data collected was subjected to analysis of variance
to test for statistical significance among treatments. Means were separated using Students
Newman Keuls test at 95% level of confidence. Molecular characterization of the
pathogens showed that A. solani had high genetic variation, while P. infestans showed low
genetic diversity. Characterization of the essential oil compounds revealed that the test
plants had many compounds and terpenes were the majority. The in-vitro experiment
revealed that both the crude extracts and the essential oils were fruitful in suppressing the
growth of the test pathogens. However essential oils were more effective than the crude
extracts (p<0.05). Among the crude extracts, garlic was the most effective biocontrol.
Ginger and garlic essential oils had similar effect to Ridomil
synthetic fungicide
(Metalaxyl-M and S-isomer, Mancozeb) which showed 100% pathogen growth inhibition.
In the greenhouse experiment, essential oils and Ridomil
synthetic fungicide did not differ
significantly (p>0.05) in lowering disease severity. The tomato plants treated with Mexican
marigold had the highest plant height (78.208±1.28) and also the highest number of leaves
(20.5±0.93) in plants inoculated with P. infestans. The treatment also exhibited the highest
fruit yields. The effects of other treatments did not vary significantly (p>0.05). Essential
oils used in the greenhouse experiment had similar effects to Ridomil fungicide and
therefore can be tapped for their antimicrobial efficacy. This study concluded that there
exists genetic variation within A. solani than in P. infestans in Mwea, Kenya. The source
of variation within them needs to be studied. This study recommends that plant extracts
and essential oils from ginger and garlic be used as bio-pesticides in management of early
and late blight diseases in tomato as they portrayed similar efficacy to ridomil synthetic
fungicide. Simpler and cheaper methods of essential oil extraction can be explored to make
the oils available for use as pesticides. | en_US |
