Biocidal effects of neem and aloe vera extracts on xanthomonas campestris pv campestris in cabbage
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Neem and Aloe vera plants which are known to have antimicrobial activity have been tested against Xanthomonas campestris pv campestris that causes black rot disease in cabbage. Black rot disease affects all cruciferous crops causing tremendous economic losses. The disease is difficult to control with the cultural methods however copper based chemicals are being used by farmers. These synthetic chemicals are not only expensive to purchase but also buildup in the environment causing adverse effects on non-target organisms. This limits their use on small scale and in a long run. Degradable biopesticides from Neem and Aloe vera plants as an alternative potential have been exploited and used by farmers with less knowledge on when and how to apply them. The method of extraction and application have been worked on in this study. This study was experimental, involving collection of Aloe vera and neem leaf samples from the botanical garden and Namulonge village respectively. The study was conducted in the research laboratory and the screen house in the botanical garden under department of Plant sciences, Microbiology and biotechnology Makerere University. This research was run for a period of four months. Samples collected were used to make extracts using water, ethanol and methanol as solvents with the objective of determining the in vitro and in vivo inhibition of Xanthomonas campestris pv campestris cultures and in cabbages respectively. Both fresh and dry sample leaves of Aloe vera and Neem were used to make extracts in different solvents Four treatments Aloe vera, Neem, Mancozeb (fungicide) as a positive control and 5% DMSO (negative controls) for extracts reconstituted in DMSO or sterile distilled water (negative control) for extracts made using water as a solvent. In vitro bioassays were performed using agar well diffusion where the zones of inhibition were measured. Both qualitative and quantitative methods were used for in vivo experiments. The cabbage seedlings were inoculated through spraying the bacterial suspension and wounding, and applied with treatments of Aloe, Neem, Mancozeb common fungicide (positive treatment), and 5 % DMSO (negative treatment) and Neem + Aloe extract after 24hrs. The seedlings were observed for symptom expression and scaled for disease severity. At the end of the experiment the plants were cut longitudinally to observe for vascular discoloration. Two experiments for both in vitro and in vivo tests were performed to achieve reliability of results. Findings in this study reveal antibacterial effects of Aloe vera and Neem against both Xanthomonas campestris pv campestris in cultures and cabbage seedlings in both experiments. The mean zone of inhibition against Xanthomonas campestris pv campestris cultures was; Fungicide (20.31mm, 23.33mm), Neem (9.45mm, 4.88mm) and Aloe vera (5.27mm, 3.28mm) DMSO and water (0mm, 0mm) for both the first and second experiment respectively. Neem + Aloe vera combination tested in the second experiment had 4.75 as the mean inhibition zone. The Mean zones of inhibition of extracts against Xanthomonas campestris pv campestris revealed a significant difference in the antibacterial activity of Aloe vera, Neem and fungicide. There was delayed symptom expression in plants treated with Neem and Aloe vera compared to 5% DMSO treated plants used as the negative control. Neem + Aloe combination performed as good as the fungicide. There was no visible v-shaped lesions and vascular discoloration for plants treated with fungicide and neem + aloe extract. The disease was more severe in plants treated with 5% DMSO, less severe in those treated with aloe and neem extracts. Plants treated with fungicide, Neem +Aloe combination did not show any disease symptoms for both experiments. Neem and Aloe vera extracts were found to have antibacterial effect and their possible combinations could enhance the modes of action of phytochemicals against black rot pathogen.