Doctoral Degrees (Plant Pathology)

Permanent URI for this collectionhttps://hdl.handle.net/10413/6639

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Biological control and plant growth promotion by selected trichoderma and Bacillus species.
(2005) Yobo, Kwasi Sackey.; Laing, Mark Delmege.; Hunter, Charles Haig.
Various Trichoderma and Bacillus spp. have been documented as being antagonistic to a wide range of soilborne plant pathogens, as well as being plant growth stimulants. Successes in biological control and plant growth promotion research has led to the development of various Trichoderma and Bacillus products, which are available commercially. This study was conducted to evaluate the effect of six Trichoderma spp. and three Bacillus spp. and their respective combinations, for the biological control of Rhizoctonia solani damping-off of cucumber and plant growth promotion of dry bean (Phaseolus vulgaris L.). In vivo biological control and growth promotion studies were carried out under greenhouse and shadehouse conditions with the use of seed treatment as the method of application. In vitro and in vivo screening was undertaken to select the best Trichoderma isolates from 20 Trichoderma isolated from composted soil. For in vitro screening, dual culture bioassays were undertaken and assessed for antagonisms/antibiosis using the Bell test ratings and a proposed Invasive Ability rating based on a scale of 1-4 for possible mycoparasitic/hyperparasitic activity. The isolates were further screened in vivo under greenhouse conditions for antagonistic activity against R. solani damping-off of cucumber (Cucumis sativus L.) cv. Ashley seedlings. The data generated from the in vivo greenhouse screening with cucumber plants were analysed and grouped according to performance of isolates using Ward‟s Cluster Analysis based on a four cluster solution to select the best isolates in vivo. Isolates exhibiting marked mycoparasitism of R. solani (during ultrastructural studies) viz, T. atroviride SY3A and T. harzianum SYN, were found to be the best biological control agents in vivo with 62.50 and 60.06% control of R. solani damping-off of cucumber respectively. The in vitro mode of action of the commercial Trichoderma product, Eco-T®, and Bacillus B69 and B81 suggested the production of antimicrobial substances active against R. solani. In vitro interaction studies on V8 tomato juice medium showed that the Trichoderma and Bacillus isolates did not antagonise each other, indicating the possibility of using the two organisms together for biological control and plant growth promotion studies. Greenhouse studies indicated that combined inoculation of T. atroviride SYN6 and Bacillus B69 gave the greatest plant growth promotion (43.0% over the uninoculated control) of bean seedlings in terms of seedling dry biomass. This was confirmed during in vivo rhizotron studies. However, results obtained from two successive bean yield trials in the greenhouse did not correlate with the seedling trials. Moreover, no increase in protein or fat content of bean seed for selected treatments was observed. In the biological control trials with cucumber seedlings, none of the Trichoderma and Bacillus combinations was better than single inoculations of Eco-T®, T. atroviride SY3A and T. harzianum SYN. Under nutrient limiting conditions, dry bean plants treated with single and dual inoculations of Trichoderma and Bacillus isolates exhibited a greater photosynthetic efficiency that the unfertilized control plants. Bacillus B77, under nutrient limiting conditions, caused 126.0% increase in dry biomass of bean seedlings after a 35-day period. Nitrogen concentrations significantly increased in leaves of plants treated with Trichoderma-Bacillus isolates. However, no significant differences in potassium and calcium concentrations were found. Integrated control (i.e. combining chemical and biological treatments) of R. solani damping-off of cucumber seedlings proved successful. In vitro bioassays with three Rizolex® concentrations, viz., 0.01g.l-1, 0.1g.l-1 and 0.25g.l-1 indicated that the selected Trichoderma isolates were partly sensitive to these concentrations whereas the Bacillus isolates were not at all affected. In a greenhouse trial, up to 86% control was achieved by integrating 0.1g.l-1 Rizolex® with T. harzianum SYN, which was comparable to the full strength Rizolex® (1g.l-1) application. Irrespective of either a single or dual inoculations of Trichoderma and/or Bacillus isolates used, improved percentage seedling survival as achieved with the integrated system, indicating a synergistic effect. The results presented in this thesis further reinforce the concept of biological control by Trichoderma and Bacillus spp. as an alternative disease control strategy. Furthermore, this thesis forms a basis for Trichoderma-Bacillus interaction studies and proposes that the two organisms could be used together to enhance biological control and plant growth promotion.
Biological control of the common house fly (Musa domestica L.) using Bacillus thuringiensis (Ishiwata) berliner var. Israelensis and Beauveria bassiana (Bals.) vullemin in caged poultry facilities.
(2008) Mwamburi, Lizzy A.
The entomopathogenic fungus Beauveria bassiana and the bacterium Bacillus thuringiensis var. israelensis (Bti) have been widely studied for their role in biocontrol against many arthropods and extensively exploited for insect pest control. The purpose of this study was to evaluate the effect of four B. bassiana and two Bti formulations and their respective combinations, for the biological control of the common house fly, Musca domestica L., a major pest in poultry facilities. In vitro screening was undertaken to select the best B. bassiana isolates from 34 B. bassiana isolates and two Paecilomyces isolates. All the isolates of B. bassiana were found to be effective against adult house flies, but were marginally effective in controlling fly larvae. The Paecilomyces isolates were non-pathogenic towards both adult house flies and larvae. The best four isolates R444, 7320, 7569 and 7771 caused >90% mortality within 2d and were subjected to dose-mortality bioassays. Microscopic studies using light and scanning electron microscopy indicated the different durations of the lifecycle of B. bassiana development on the house fly. High temperature was found to delay conidial germination. Spore germination and mycelial growth were also inhibited by high adjuvant concentrations. Laboratory baseline bioassay data established, a dose-time response relationship using a waterdispersible granules (WDG) Bti formulation that demonstrated that the susceptibility of M. domestica larvae to a given concentration of Bti increased as the duration of exposure increased. In the laboratory studies, the LC50 and LC90 values of Bti for the larvae ranged between 65 - 77.4 and 185.1 - 225.9?g ml-1, respectively. LT50 and LT90 values were 5.5 and 10.3d respectively. In the field, a concentration of 10g Bti kg-1 (bran formulation) of feed resulted in 90% reduction of larvae for 4wk post-treatment. A higher concentration (2g L-1) of Bti in spray (WDG) applications was not significantly more effective than the lower concentration of 1g L-1. Thus, adding Bti to chicken feed has potential for the management and control of house flies in cagedpoultry facilities. The impact of oral feed applications of a bran formulation of Bti and a commercial chemical larvicide, Larvadex®, were compared with respect to their efficacy on the control of house fly 3 larval populations in poultry manure. The sublethal effects were manifested in terms of decreasing emergence of adult house flies. Although Larvadex® reduced larval density and caused significant reductions in emergence of adult house flies, it generally exhibited weaker lethal effects than Bti. The reduction levels achieved as a result of feeding 250mg Bti kg-1 at 5wk were similar to those achieved as a result of feeding twice the amount of Larvadex® at 4wk to the layers. From both an efficiency and economic perspective, comparisons to assess the impact of combining different concentrations of the two Bti formulations were carried out to evaluate their success in controlling house fly larvae and adults in poultry houses. The percentage mortality of larvae accomplished as a result of using a combination of 250mg kg-1 Bti in feed and 2g L-1 spray applications was equivalent to that obtained as a result of combining 500mg kg-1 Bti in feed and 1g L-1 spray application. The cost-benefit analysis (expressed in terms of mortality of larvae) indicated that the most effective combination for control of house fly larvae and fly emergence was the 500mg kg-1 in feed and 2g L-1 spray application combination that resulted in 67% larval mortality and 74% inhibition of adult house fly emergence. This study presents commercial users with possible combinations of applications of the two Bti formulations. Comparisons of larval mortalities and house fly emergence resulting from the Bti - B. bassiana treatments with those from Larvadex® - B. bassiana treatments, showed better control levels compared to any of the individual agents alone. The Bti treatments were more effective at controlling larval populations and inhibiting the emergence of house flies than Larvadex®, even when Larvadex® was applied together with B. bassiana. The effects of the Bti - B. bassiana and the Larvadex® - B. bassiana interactions were additive. These trials suggest that the efficacy of Bti in the control of house fly larvae may be improved with frequent applications of B. bassiana.
Isolation of entomopathogenic gram positive spore forming bacteria effective against coleoptera.
(2009) Du Rand, Nicolette.
Fourteen spore-forming bacterial strains were isolated and screened for entomopathogenic activity. Five displayed toxicity towards the common mealworm, Tenebrio molitor L., (Coleoptera: Tenebrionidae). The majority of the isolates were obtained from insect larvae and insect rich environments. The three bacterial species identified were Bacillus thuringiensis Berliner, Brevibacillus laterosporus Laubach and Bacillus cereus Frankland and Frankland. Bioassays were conducted using T. molitor larvae. The one isolate of B. cereus required the highest concentration of bacterial cells to achieve its LC50, whereas one of the isolates of B. laterosporus required the lowest cell concentration to achieve its LC50. Dose response curves were generated for the five best isolates, which showed that the isolate of B. laterosporus (NDR2) was substantially more toxic than the other isolates.

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Browsing Doctoral Degrees (Plant Pathology) by Subject "Bacillus (Bacteria)"