natural-products-in-plant-pest-management

Control of Mycotoxins and Mycotoxigenic Fungi 23polygalacturonase-inhibiting proteins and α-amylases have been shown topossess antifungal activity against toxigenic fungi. When attacked by insectsand pathogens, plants produce, together with defence proteins, a wide varietyof volatile and non-volatile secondary metabolites, such as phytoalexins,alkaloids, terpenes, aldehydes, etc.Much research has been published on the antimicrobial activity ofplant products, including flours, plant extracts, oleoresins and essentialoils. A very interesting option is the use of essential oils as antimicrobialadditives, because they are rich sources of biologically active compounds.Essential oils are mainly obtained by steam distillation from various plantsources.The antimicrobial activity of plant products has been extensively studiedand demonstrated against a number of microorganisms, mostly in vitro ratherthan in tests with foods, and usually using a direct-contact antimicrobialassay. In the direct-contact method, active compounds are brought into contactwith the selected microorganisms, and their inhibition is monitored bymeans of direct inspection or by measuring a physical property that is directlyrelated to microorganism growth, such as optical density, impedance or conductance.The solution of active compound may be added to a test tube or toagar medium, and then microorganisms are inoculated. The disc diffusiontest consists of spiking a sterile disc with the active compound; spiked discsare then added after inoculation of the medium, after which the inhibitionzones are measured, giving an indication of the antimicrobial strength. Forvolatile compounds such as essential oils, the antimicrobial effectiveness inthe vapour phase is of particular interest. This variety of testing techniquesmakes it difficult to compare results obtained by different researchers, mainlybecause of the difficulty in knowing the concentrations of active compoundsapplied.In vitro assays against mycotoxigenic fungiMany plant extracts have been tested in vitro for antifungal activity against awide range of fungi associated with deterioration of food commodities andherbal drugs.Studies carried out by Karthikeyan et al. (2007) revealed that aqueousleaf extract of zimmu (an interspecific hybrid of Allium cepa L. and Alliumsativum L.) exhibited strong antifungal activity against Aspergillus flavus,Fusarium moniliforme and Alternaria alternata and caused in vitro fungalgrowth inhibition of 73.3%, 71.1% and 74.4%, respectively. These mouldscause mouldy sorghum grains. Essential oil and methanol extract of Saturejahortensis had strong activity against A. flavus isolated from lemon fruit(Dikbas et al., 2008).Extracts of Cynara cardunculus were effective in the control of A. flavus,A. niger, A. ochraceus, Fusarium tricinctum, Penicillium funiculosum, P. ochrochloron,Trichoderma viride and Alt. alternata (Kukic et al., 2008). Similar resultswere obtained with aqueous extract of Adenocalymma sativum in order to