natural-products-in-plant-pest-management

24 S. Marín et al.control A. flavus, A. niger, A. terreus, F. oxysporum, F. roseum, P. italicum, Cladosporiumcladosporioides and Alt. alternata. The minimum inhibitory concentrationof extracts against A. flavus and A. niger were superior to those of twocommonly used synthetic fungicides (Shukla et al., 2008).The essential oil of Amomum subulatum exhibited a fungitoxic spectrumagainst a wide range of moulds such as A. niger, A. flavus, A. terreus,A. fumigatus, Alt. alternata, Cladosporium herbarum, Curvularia lunata, F. oxysporum,Helminthosporium oryzae and Trichoderma viride. Their mycelial growthwas significantly inhibited at 750 μg/ml (Singh et al., 2008a).An in vitro initial screening of a range of 37 essential oils (includingcinnamon leaf, Cynnamomum zeylanicum; clove, Syzygium aromaticum; lemongrass,Cymbopogon citrates; oregano, Origanum vulgare; and palma rose,Cymbopogon martinii) on inhibition of mycelial growth of toxigenic strains ofF. verticillioides, F. proliferatum and F. graminearum under different temperatures(20–30°C) and water activities (a w) (0.95–0.995) was made. The basicmedium was a 3% maize meal extract agar. The agar medium was modifiedwith glycerol in order to get the assayed water activity and the essential oilswere incorporated at different concentrations (0, 500, 1000 μg/ml). Althoughwater activity was determinant for the growth of the isolates, in general, thepreservative effects of the oils were not linked to a w. However, a trend to ahigher inhibition by the oils when a wwas low was observed. Temperaturehad a minor importance in the inhibitory effect of the essential oils (Vellutiet al., 2004a).Essential oils of both cinnamon and clove were shown to effectivelyinhibit growth of both A. flavus and P. islandicum by direct contact, and in thevapour phase. In the atmosphere generated by these two essential oils eugenolwas the major compound, while other essential oils with low levels ofeugenol proved to be ineffective, suggesting that eugenol was the antimicrobialagent (López et al., 2005).Guynot et al. (2003) proved that the volatile fractions of cinnamon leaf,clove, bay (Laurus nobilis), lemongrass and thyme (Thymus vulgaris) showedpotential antifungal activity against A. flavus and A. niger.In vitro assays for the inhibition of mycotoxin productionSpecies in Aspergillus section Flavi, mainly A. flavus and A. parasiticus areamong the most commonly occurring spoilage fungi. Some strains of thesespecies have the ability to produce aflatoxins. These fungi invade agriculturalcommodities such as corn, peanuts and cottonseed, and herbal drugs,the resulting contamination with aflatoxin often making these pro ducts unfitfor consumption. Moreover, these mycotoxins are considered carcinogenicsubstances and their presence is a health concern, so their control is one ofthe aims in order to obtain safe products. Little attention has been paid, however,to the efficacy of essential oils in inhibiting aflatoxin production.Recently, work has been carried out to study the effect of these products asanti-aflatoxigenic agents.