| dc.description.abstract | Work was done on formulation of crude antibiotic metabolites produced by
Bacillus spp. isolates coded CAS and CA10 obtained from Dr.E.W.Mutitu,
Department of Crop Protection,University of Nairobi where they had been preserved
over 2 years in sterile soil at room temperature. Their efficacy in controlling plant
pathogens of economic importance was determined. The coded isolates had been
characterised and found to conform to Bacillus subtilis species both in physiological
and morphological characteristics. They had also been proven to be antagonistic to
various plant pathogens.
Invitro studies on growth of C. kahawae, C. lindemuthianum and Alternaria
sesami showed strong inhibition by the retrieved antagonistic Bacillus isolates CAS
and CA 10. Fusarium oxysporum f.sp phaseoli was found to be less sensitive to the
same isolates. Bacillus isolate CAS exhibited greater inhibitory activity on all the
fungal pathogenic isolates tested as compared to isolate CA 10 when tested under
the same conditions.
The recovery of antibiotic metabolites from isolates CA 1a and CAS grown in
shaken liquid medium containing soymeal, glucose, glycerol, yeast and mineral salts
was 4% and 2.4%, respectively. However, the antibiotic metabolites from isolate
CAS were found to be more inhibitory to the test fungal pathogens than those of
isolate CA 1a.
The culture filtrate containing the antibiotic metabolites from isolates CAS and
CA 1a took 12-24 hrs to dry in a freeze drier at -11 aOc. The final product was
chocolate (deep) brown tar-like material from isolate CAS and brown incase of isolate
CA 1O. The two products were highly hygroscopic and dissolved easily in water. The
antifungal activity of both products was retained even after freeze drying.
The freeze-dried antibiotic metabolites dissolved easily in propylene glycol,
which was used for formulation without significant sedimentation. The solubility was
better with isolate CA5 antibiotic metabolites (1 gm I 6 ml) than isolate CA10 (1 gm I
8 ml). The formulated solution concentrate showed antifungal activity on C. kahawae
and C. lindemuthianum in vitro.
The antibiotic solution concentrate of Bacillus isolates CA10 and CA5, diluted
at 1:3 (antibiotic: water), inhibited sporulation of C. kahawae on coffee twigs by
84.5% and 89.7%, respectively. The percentage sporulation inhibition from both
isolates was comparable to 84.5% achieved with a broad-spectrum protectant
fungicide Dithane M45 80 % WP.
Greenhouse experiments with the formulated antibiotics reduced bean
anthracnose severity and delayed symptom development. On the 5th week, isolate
CA5, isolate CA10 and Dithane M45 gave a mean disease score of 2.6, 2.9 and 1.2
respectively compared to 6.2 recorded in the control. At higher concentrations the
antibiotics were found to be phytotoxic to treated bean plants. The formulated
antibiotics effectively controlled coffee berry disease on coffee seedlings without
showing any phytotoxic effects. The mean disease score of coffee seedlings treated
with isolate CA5, isolate CA10 and Dithane M45 was 2.4, 2.8 and 2.0 respectively
compared to 3.8 recorded in the control.
Using the filter paper disc bioassay method, the freeze dried culture filtrate of
Bacillus isolates CA5 and CA10 were found to lose antifungal activity after storing
them in the refrigerator at 4°c for one year. No inhibition zones were detected with
Col/etotrichum kahawae, C. lindemuthianum, Alternaria sesami and Fusarium
oxysporum f.sp. phaseoli the test fungal pathogens. | en |
