natural-products-in-plant-pest-management

70 J.C. Pretorius and E. van der Wattthe active substances were found for the first time. The highest growthinhibition of this bacterium was recorded for extracts of Aloe arborescens,Juglans regia, Rhus typhina (R. hirta), Salvia officinalis and Satureja hortensis. Inalmost all cases ethanol appeared to be a better solvent of active plantsubstances against E. amylovora than water.A similar approach was followed by Morais et al. (2002) in screeningcrude extracts of 45 known medicinal plants against bacterial pathogens oftomato. The antibacterial activity of crude extracts was tested against Xanthomonascampestris pv. vesicatoria, Ralstonia solanacearum and Clavibacter michiganensesubsp. michiganense. Some assays were also performed to verify thecapability of these plant extracts to show antibiosis. Five of the 45 extractsshowed significant activity against the test bacteria, confirming the potentialof using either these extracts or active substances contained in them as naturalproducts under field conditions. In the same year, Devanath et al. (2002)compared the antibacterial effect of extracts from three medicinal plants(Psidium guajava, Aloe vera [A. barbadensis] and Datura stramonium) to twostandard fungicides (Streptocycline and Blitox or copper oxychloride) againstRhizoctonia solanacearum in vitro. The aqueous extract of Aloe vera was mosteffective in suppressing the growth of R. solanacearum followed by the extractof Psidium guajava.Zeller et al. (2002) reported on the effect of an extract from Hedera helixagainst fire blight on pome fruits, caused by Erwinia amylovora. The highestgrowth inhibition of this bacterium was recorded for extracts of Aloe arborescens,Juglans regia, Rhus typhina (R. hirta), Salvia officinalis and Satureja hortensis.In almost all cases ethanol appeared to be a better solvent of active plantsubstances against E. amylovora than water. Also using the bacterium E. amylovoraas a test organism, Jin and Sato (2003) searched for secondary metabolitesin aqueous extracts from succulent young shoots of pear (Pyrus).Aqueous extracts of the tissue of succulent young shoots exhibited strongantibacterial activity against E. amylovora. The active compound was isolatedfrom the extract by steam distillation in vacuo, purified through charcoalpowder column chromatography and identified as benzoquinone (2,5- -cyclohexadiene-1,4-dione) by NMR spectra, mass spectra and HPLC analysis.In the same year, Pretorius et al. (2002a) demonstrated the broad-spectrumantibacterial activity of crude extracts from Acacia erioloba, Senna italica andBuddleja saligna against the plant pathogens Agrobacterium tumefaciens,Clavibacter michiganense pv. michiganense, Erwinia carotovora pv. carotovora,Pseudomonas solanacearum and Xanthomonas campestris pv. phaseoli.Additionally, plant extracts with antibacterial properties can provide analternative to certain antibiotics. Zeller et al. (2002) reported on such alternativesto the antibiotic streptomycin for the control of fire blight on pomefruits, caused by E. amylovora, which is of great economic importance forGerman and European fruit producers. An antagonistic preparation,BIOPRO, showed a control efficacy of up to 60% and the plant extract fromHedera helix revealed a high efficacy in the field in combination with a lowconcentrated copper compound and a metal salt. The control of fire blight inthis manner was comparable to that by the antibiotic streptomycin under