MANAGEMENT OF BACTERIAL WILT (Ralstonia solanacearum) OF POTATO (Solanum tuberosum) USING PLANT EXTRACTS AND HOST PLANT RESISTANCE

Abstract

Potato (Solanum tuberosum L.) is ranked second after maize among Kenya's most grown food crops. However, its production is constrained by bacterial wilt (Ralstonia solanacearum) disease. The objectives of this study were: to evaluate different potato genotypes for resistance to bacterial wilt in the field; to determine in-vitro antibacterial activity of different plant extracts against R. solanacearum of potatoes; to elucidate the bioactive compounds effective in managing R. solanacearum and to determine the synergistic effect of plant extracts and host plant resistance in the management of bacterial wilt (Ralstonia solanacearum) of potatoes under greenhouse conditions. Thirty potato genotypes were screened for resistance to R. solanacearum in the field at Turi, Nakuru County and Kiandu, Nyeri County using an alpha lattice design with 3 replicates for 2 seasons. In-vitro screening of antibacterial activity of plant extracts against R. solanacearum was conducted using disk diffusion technique and the experiment was arranged in a Completely Randomized Design (CRD). The bioactive compounds from the most effective plant extracts were identified by gas chromatography-mass spectrometry (GC-MS). Greenhouse experiment was arranged in a CRD of 2*6 factorial arrangements with 3 replicates. Data was collected on disease incidence, disease severity, plant growth and yield parameters, colony counts and growth inhibition zones. Data were subjected to analysis of variance (ANOVA) at p<0.05 using R software, version 4.3.1 and the treatment means separated using Tukey’s Honestly Significant Difference (HSD). Field screening results ranked genotypes CIP 515004.535 and CIP 515008.561 as highly resistant and Shangi, Asante, Tigoni, Arka and CIP 515008.535 as highly susceptible. In-vitro results revealed that Pelargonium zonale leaves extract as the most effective extract with growth inhibition zone of 18.73mm followed by Psisdium guajava with growth inhibition zone of 14.27mm. Both P. zonale and P. guajava had 7 similar antibacterial compounds; Fumaric acid, Pyrogallol, 4-Hydroxybenzoic acid, Shikimic acid, Protocatechuic acid, 3, 4, 5-Trihydroxybenzoic acid ethyl ester but P. zonale had Lactic acid as an additional compound. Sherekea exhibited the highest average efficacy from the two plant extracts; 0.14 for disease incidence, 1178.21 for AUDPC, 1.84 for stem height, 2.66 for bacterial wilt colony counts and 0.28 for yield (Kgs) respectively from the greenhouse experiment. These results revealed effective synergistic effect of botanicals and host plant resistance in management of potato bacterial wilt and hence should be promoted as integrated disease management option.