| dc.description.abstract | Irish potato (Solanum tuberosum L.) is a major cash and food crop worldwide. The
production of this crop has in a great way been negatively affected by the extensive
spread of bacterial wilt that is caused by Ralstonia solanacearum with over 50% crop
yield losses reported in the last two decades. In addition, no bactericide has been
developed to combat the disease and exercise of integrated control measures have not
resulted to a sustainable solution. Scientists are putting a lot of efforts in research to get a
solution that is effective, environmental friendly and that will enable the capacity of food
production be improved to cater for the increasing human population. Plants have been
shown to contain principles which are active against pathogens and among them are
Brassica, Ipomoea and Ocimum species. It is on this basis that this research was aimed at
determining the efficacy of locally available plants extracts in controlling the bacterial
wilt disease in potatoes. The study was carried out in Maseno University Botany &
Horticulture Department laboratory and the institution's Botanic Garden in 2007. The
pathogen was isolated from infected potato tubers and cultured on nutrient agar medium.
Ethyl acetate and methanol extracts of leaves of Ocimum gratissimum, Ipomoea batatas
and Brassica oleracea var. botrytis and essential oils of. Ocimum gratissimum were
evaluated for their efficacy at concentrations of 0.4, 0.2, 0.1, 0.05 and 0.025 mg/ml
dissolved in dimethylsulphoxide in inhibiting in vitro growth of wilt bacteria. The
experiment was extended to greenhouse where aqueous extracts of the three plants at
concentrations of 2.5, 5 and 10% were evaluated for their efficacy in controlling the
development of bacterial wilt symptoms on inoculated potato plants with control plants
being inoculated with no treatment subjected to them. The extracts were also evaluated
for their effect on different potato plants parameters. The experimental set up was randomized completely block design with 12 treatments and three replications. Data
collectedwas subjected to Analysis of Variance (ANOVA) using SAS statistical package
and the effects declared significant at 5% level. Linear correlation was used to compare
the relationship between variables. The study has proved that the three plants contains
principles that are active against wilt bacteria with essential oils from Ocimum
gratissimum at O.4mglml exhibiting highest activity (10.lmm inhibition diameter) and
Ipomoea batatas methanol extract at 0.025mglml exhibiting zero inhibition. The
laboratory study has also shown a highly significant (P < 0.0001) interaction among
plants, solvents and the various concentrations in the inhibitory activity. Aqueous extracts
of the three plants have also exhibited varying levels of controlling wilt symptoms and
promoting potato growth. The extracts of Ocimum at 10% and Brassica at 5% were the
most effective in controlling the development Of wilt symptoms with average wilting
index of 1.33 meaning less than 50% wilting occurrence. Potato plants treated with
Brassica extracts at 10% exhibited an abnormal character of its leaf tips drying and thus
.affecting their growth. In assessing the effect of potato wilting, the interaction between
the plant and various concentrations was shown not to be significant (P> 0.05) in the first
four days after inoculation. However it was significant (P<O.001) in the following three
days and highly significant (P< 0.0001) after and until the end of the study period. The
crude extracts had a significant effect on the growth parameters of potato. Based on the
findings of this study the three plants contains compounds that are active against the
growth of wilt bacteria and we recommend further evaluation of the crude extracts to
determine the actual active ingredients which can be used to develop an effective
biocontrol agent for this disease. | en_US |
