Determination of Bioactive Compounds Against Bacterial Wilt of Potato (Ralstonia pseudosolanacearum sp. nov.) in Psidium guajava and Pelargonium zonale Leaf Extracts

Common guava (Psidium guajava) and Pelargonium (Pelargonium zonale) have shown in-vitro antibacterial activity against Ralstonia pseudosolanacearum sp. nov. in previous studies. However, their phytochemical constituents and bioactive compounds against the pathogen have not been identified. The present study investigated the phytochemical components of P. guajava and P. zonale leaf extracts by phytochemical screening and gas chromatography-mass spectrometry (GC-MS). Phytochemical screening was done using different solvents while 100 mg of the dried ethanolic extract pastes from each plant sample was subjected to GC-MS analysis. Automated mass spectral deconvolution and identification system software (AMDIS, US) was used to analyze chromatograms and spectra representing individual compounds. Compound identification was performed by comparing each of the mass spectra with the database of NIST 11 (Gaithersburg, MD, USA), Wiley 7N (John Wiley, NY, USA) and by comparing the calculated Kovats linear retention indices using retention times of n-alkane series against the values in the NIST webbook. Flavonoids, phenols, alkaloids, saponins, terpenoids and tannins were detected in both plant samples. GC-MS analysis revealed presence of 35 and 26 compounds from P. zonale and P. guajava respectively. Both P. zonale and P. guajava had 7 similar compounds with antibacterial properties; Fumaric acid, Phytol, Pyrogallol, 4-Hydroxybenzoic acid, Shikimic acid, Protocatechuic acid and 3, 4, 5-Trihydroxybenzoic acid ethyl ester but P. zonale had one additional antibacterial compound; Lactic acid. In both cases, Shikimic acid had the highest percent peak areas of 3.2% for P. zonale and 6.8% P. guajava respectively. Therefore, P. zonale and P. guajava can serve as alternative sources of active ingredients for formulation of commercial botanicals for the management of bacterial wilt of potato.