natural-products-in-plant-pest-management

Natural Products from Plants 47Chrysanthemum cinerariefolium, and neem seed from Azadirachta indica( Richard, 2000), has a long history in plant protection.Despite the fact that reports on the practical application of natural plantextracts towards the control of plant pathogens in modern agriculture arefound less frequently in the literature (Menzies and Bélanger, 1996), aconsiderable number of reports on natural chemicals that are biologicallyactive against various plant diseases is currently available. These naturalcompounds are usually secondary metabolites and are synthesized in plantsas a result of biotic and abiotic interactions (Waterman and Mole, 1989;Helmut et al., 1994). By means of bioassay guided screening, a number ofthese natural plant compounds, with antimicrobial activity, have beenisolated and progress has also been made towards the identification andstructural elucidation of these bioactive compounds (Grayer and Harborne,1994). Although extractable secondary metabolites have long been consideredas an important source of pharmaceuticals, the evaluation of their applicationpotential in crop production systems has been largely neglected. A widerange of activities with both positive and negative effects, including the controlof microorganism, plant growth regulation (Adam and Marquardt, 1986),the induction of plant resistance to various diseases (Daayf et al., 1995;Schmitt et al., 1996) and promotion of beneficial microorganisms in the soilrhizosphere (Williams, 1992) have been reported. Despite these efforts, theisolation of plant secondary metabolites has led to very few commercialsuccesses in the agricultural industry and more specifically in crop managementpractices.An accelerated search for alternative options to synthetic fungicides,based on natural products from plants, therefore, seems to be an importantconsideration in light of the current restrictions in pesticide use in both developedand developing countries. This especially applies to the search forenvironmentally friendly bioactive components with broad-spectrum antimicrobialactivity (Benner, 1993). This probably needs serious considerationin developing countries where yield losses are high as a result of low-inputproduction systems due to the unaffordability of synthetic fungicides to localfarmers.According to the Natural Antifungal Crop Protectants Research Agency(Hall, 2002) spoilage and plant pathogenic fungi are responsible for some20% loss of the potential global plant production for food and non-food use.The very large amount of chemical crop protectants used to control theselosses can be detrimental to both the environment and human health.Therefore research has been initiated to develop and implement non- syntheticcrop protectants using natural antifungal agents (green chemicals) orantifungal metabolites from plants. These natural crop protectants will bedesigned for use on food or non-food crops vulnerable to fungal deterioration(Hall, 2002). From an agronomic perspective, a secondary aim of researchon natural plant products is to cultivate bioactive plants, as alternativeagricultural crops, to serve as sources for the bioactive compounds.Despite the inherent potential of compounds from plants to be applied asnatural products in agriculture, cognizance has to be taken of problems