natural-products-in-plant-pest-management

26 S. Marín et al.well as aflatoxin production at a concentration lower than with the individualoils (Srivastava et al., 2008).The results obtained by Sandosskumar et al. (2007) in in vitro experimentsconfirmed the antifungal activity of the zimmu extract against toxigenicstrains of A. flavus. In addition, when the aflatoxigenic strains were grown inmedium containing zimmu extract the production of AFB 1was completelyinhibited, even at a concentration of 0.5%. In addition, when AFB 1was incubatedwith this extract a complete degradation of the toxin was observed5 days after incubation. It is possible that the reduction in AFB 1content maybe due to detoxification or catabolism of AFB 1by root exudates of zimmu.Molyneux et al. (2007) suggested the hypothesis that aflatoxin biosynthesisis stimulated by oxidative stress on the fungus and the compounds capableof relieving oxidative stress should therefore suppress or eliminate aflatoxinbiosynthesis.Srivastava et al. (2008) concluded that, in general, the inhibitory action ofnatural products on fungal cells involves cytoplasm granulation, cytoplasmicmembrane rupture and inactivation and/or inhibition of synthesis of intracellularenzymes. These actions can occur in an isolated or in a concomitantmanner and culminate with mycelium germination inhibition. Phenolic compoundsin the essential oils have been mostly reported to be responsible fortheir biological properties; however, some non-phenolic constituents of oilsare more effective. The aldehyde group is also believed to be responsible forantimicrobial activity. Among the alcohols, longer chain (C6–C10) moleculesin the oils have been reported to be more effective. Such compounds presentin the oils may be held responsible for such biological activities.In addition, the therapeutic use of essential oils and their combinationscomprising more than one fungitoxic ingredient may also provide a solutionfor the rapid development of fungal resistance which is currently noticed incases of different prevalent antifungal therapeutics. Results obtained by otherresearchers (Sidhu et al., 2009) confirmed the synergistic effect of plantextracts. So, the combination of botanicals can be used for control of fungalgrowth and aflatoxin production.Another mycotoxigenic mould is P. expansum, which is mainly responsiblefor decay in apples and pears kept in cold storage rooms. In addition, it isregarded as the major producer of the mycotoxin patulin. When applesinvaded by P. expansum are used in making apple products (e.g. fruit juices),these products will probably be contaminated with patulin. Its presence is ahealth concern.Neem leaf extracts inhibited patulin production at concentrations higherthan 12.5 mg/ml, reaching a 96% inhibition at 50 mg/ml of neem extract.Patulin concentrations were reduced by neem extracts in cultures whose growthwas not inhibited. So, the inhibition of patulin production does not appear tobe simply a function of mycelial weight reduction (Mossini et al., 2004).The aldehydes hexanal, trans-2-hexenal, citral, trans-cinnamaldehydeand p-anisaldehide, the phenols carvacrol and eugenol, and the ketones2-nonanone and (–)-carvone were screened for their ability to controlP. expansum conidia germination and mycelial growth (Neri et al., 2006).