Effect of Essential Oil Plant Extracts on in vitro Growth of Ralstonia solanacearum
Ralstonia solanacearum is a soil-borne plant bacterial pathogen that causes wilting of affected plants. The disease is a major menace to many plants especially those from Solanaceae family that include potatoes and tomatoes which are major food crops. Control of bacterial wilt disease is generally very difficult as there are no effective curative chemicals. Furthermore the pathogen can survive as a latent infection in some non-host plants thus compounding control strategies. This study is aimed at investigating the potential roles of plant essential oils in managing this pathogen. Effects of each extract on growth of R. solanacearum was determined using a modified Kirby-Bauer disc diffusion method by impregnating filter discs with the extract and then placing them on an inoculated medium followed by incubation at different growth temperatures. The sizes of inhibition zones were measured and statistical analysis performed with the GenStat 12.1 (PC/Windows XP). Fisher’s protected least significant difference test was used to separate the means. Results demonstrated that essential oils extracted from Ocimum suave , Lippie javanica and Tarchonanthus camphorates possess antibacterial activity that is effective in control of R. solanacearum
at 24oC, 28oC and 32oC. Activity by O. suave was significantly higher
(P<0.05) compared to the other plants by producing largest inhibition zone of 5.78 ± 0.08mm at 24oC. In general the best activity at all incubation temperatures was in plates kept for 24 hours. An important finding is that essential oils activity against R. solanacearum did not indicate tendancy for disease resistance as was the case with chloramphenicol an antibiotic that was used as a positive control. This study shows that essential oil plants represent a rich potential source of alternative and perhaps environmentally acceptable disease management compound (s) that is active against R. solanacearum.
Key words: Antibacterial, Essential oils, Inhibition zone, Ralstonia
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