ANTIMICROBIAL EFFICACY OF THYMOL IN THE MANAGEMENT OF BACTERIAL WILT OF TOMATO

Abstract

Bacterial wilt (BW), caused by Ralstonia solanacearum, is a devastating disease of tomato world-wide. The disease is responsible for more than 60% reduction of tomato yield in Nigeria. Volatile plant essential oil, thymol, was evaluated against BW in artificially-inoculated potted plants.  Twenty milliliter of 10⁸ cfu/ml suspension of Ralstonia solanacearum was introduced into 5 kg pot of sterilized soil and 20 ml each of three concentrations of thymol (0.2, 0.4, 0.6 g/L) applied as pre-plant soil drench 2 hours after bacterial inoculation.  Eight tomato genotypes were transplanted into the pots five days after thymol application.    The experiment was laid in a completely randomized design (CRD) with three replicates.  At 0.2 g/L thymol application, disease severity index was 1.50-4.00 at 5 Weeks After Transplanting (WAT).  Disease severity index was reduced significantly (p<0.05) by 77.78% in tomato variety Delila upon 0.4 g/L application of thymol. At 0.6 g/L thymol application, tomato varieties Delila, Perfect Pee and Kerewa each had 0 (zero) disease severity index, while tomato lines NG/AA/MAY/09/030, NG/TB/AUG/09/006 and NG/AA/SEP/09/037 had disease severity index of 1 (one) each.  These results indicated that application of thymol (0.6 g/L concentration, 1:250, thymol:soil, v:w) in potted experiment was effective in reducing the severity index of bacteria wilt of tomato caused by Ralstonia solanacearum, and is therefore recommended for management of the disease.