natural-products-in-plant-pest-management

Natural Products from Plants 69fungicides have been effective in inhibiting teliospore germination of Tilletiaindica, the causal agent of Karnal bunt of wheat. This disease is becomingmore widespread, in part, because of the lack of effective chemical control.Various extracts of native plants from Sonora, Mexico were evaluated todetermine their antifungal activity against T. indica. Dichloromethane andmethanol extracts were incubated with the fungus to measure the inhibitionof mycelial growth. Dichloromethane extracts from Chenopodium ambrosiodesand Encelia farinosa reduced radial mycelial growth significantly, but totalinhibition occurred at a relatively high concentration of 500 mg ml –1 of thedichloromethane extract from Larrea tridentata. Teliospores subjected to treatmentwith the latter plant extract showed no viability when transferred tofresh culture media, confirming the extract’s potential to be applied ascontrolling agent for T. indica (Rivera et al., 2001).Plants with antibacterial propertiesAlready in the 1990s, the application of natural plant extracts under bothgreenhouse (Blaeser and Steiner, 1999; Nikolov et al., 1999; Scholz et al., 1999)and postharvest (El-Ghaouth et al., 1995; Bhaskara et al., 1998) conditionsagainst various pathogens confirmed the potential of natural compoundsfrom plants to be developed into commercial products. Although the numberof natural products applied in biological control systems is currently arelatively small percentage of the total world market, it is predicted toincrease substantially. This implicates the possible decrease of pesticideapplication in agriculture in the future. In turn, this approach could create asignificant market opportunity for alternative products to be applied on alarger scale in organic crop production systems.A vast number of reports on large-scale screening programmes to evaluatewild plants for antibacterial activity are available in the literature; werefer to only a few. The antibacterial and antifungal activities of 38 plantsbelonging to 17 families were tested by Ghosh et al. (2000). The solventextracts of different morphological parts of these plants were tested against14 bacterial and 18 fungal strains. Out of these, Alpinia mutica, Cephalandraindica, Croton bonplandianum, Curcuma amada, Holarrhena antidysenterica, Moringaoleifera and Zingiber spectabile were found to contain antimicrobial properties(Ghosh et al., 2000). Khan and Omoloso (2002) studied the antibacterialand antifungal activities of methanol extracts of Harpullia petiolaris leaves,stems, root barks and heartwoods (collected from Papua New Guinea). Antibacterialactivities were found to be highest in fractions of root bark, petroland dichloromethane fractions of stem bark, the petrol fraction of heartwoodand the butanol fraction of leaves. Antifungal activity was only observed inthe petrol fractions of the root bark and stem heartwood.Ethanol and water extracts of leaves, flowers, shoots, bark and fruits of30 herbal and woody plant species were tested for in vitro growth inhibitionof Erwinia amylovora by Krupinski and Sobiczewski (2001) using an agar diffusionmethod. Active extracts were found in 23 species, while in 13 of these