Evaluation of botanicals against Ralstonia solanacearum causing bacterial wilt of solanaceous crops

In vitro studies were conducted on aqueous and organic extracts of 18 botanicals at varying concentrations against R. solanacearum isolates obtained from tomato, brinjal and capsicum through paper disc, plate disc and spectrophotometer methods. White weed (Ageratum houstonianum), siam weed (Chromolaena odorata) and mint (Mentha viridis) at 100% concentration of extract caused maximum inhibition against all the tested isolates of R. solanacearum by paper disc method. The spectrophotometer method revealed that margosa (Azadirachta indica) extract at all the concentrations was most inhibitory against tomato isolate followed by buttercup (R. muricatus) and white weed (Ageratum houstonianum). The aqueous extract of margosa with 0.20, 0.24, 0.37 and 0.64 Od value at 100, 50, 25 and 10% concentrations with corresponding cfu/ml values 1.64x10², 1.96x10², 3.03x10² and 5.24x10², was most inhibitory followed by white weed and buttercup against capsicum and brinjal isolates. In case of test chemicals, streptocycline was most inhibitory followed by copper oxychloride. The aqueous extract of buttercup at all the concentrations was most effective to tomato isolate of R. solanacearum whereas aqueous extract of margosa and buttercup was found most inhibitory against brinjal and capsicum isolates, respectively. In vitro efficacy of margosa at 100% concentration showed maximum inhibition against tomato and capsicum isolates by plate disc method. Maximum inhibition was shown to brinjal isolate (6.67 mm) with the organic extract of mint (Mentha viridis) at 100% concentration. The organic extracts of margosa followed by buttercup and white weed were at par and found most effective against tomato isolate by spectrophotometer method. In case of brinjal and capsicum isolates, however buttercup at all the four concentrations was found to be most inhibitory followed by white weed and margosa.