natural-products-in-plant-pest-management

HOCH 2Compound 3Natural Products from Plants 61which exhibited significant antifungal activity against Botrytis cinerea, Botryosphaeriadothidea and Colletotrichum gloeosporioides (Glomerella cingulata).Flavonoid classes most often associated with antifungal activity are flavanones,flavonols, certain biflavones, chalcones and dihydrochalcones. Forexample, three glycosides isolated from Terminalia alata (T. elliptica) rootsshowed antifungal activity against the plant pathogen Aspergillus niger and thehuman pathogen Candida albicans at extremely low concentrations of between25 and 32 ppm (Srivastava et al., 2001). The three new glycosides identifiedwere: compound 1, 3,3’-di-O-methylellagic acid 4-O-β-d-glucopyranosyl-(1,4)-β-d-glucopyranosyl-(1,2)-α-l-arabinopyranoside; compound 2, 5,7,2’-tri-Omethyl-flavanone4’-O-α-l-rhamnopyranosyl-(1,4)-β-d-glucopyranoside andcompound 3, 2-α,3-β,19-β,23-tetrahydroxyolean-12-en-28-oic acid 3-O-β-d-galacto-pyranosyl-(1,3)-β-d-glucopyrano-side-28-O-β-d-glucopyrano-side(Fig.3.27). Compound 1 was a glycoside of an ellagic acid, whereas compounds 2and 3 were a flavanone glycoside and a triterpene saponin, respectively.Saponins are one of several groups of compounds that originate from triterpenoidsand show a wide range of biological activities. For instance, fungicidaltriterpenoid saponins, which also have molluscidal activity, have beenisolated from roots of Dolichos kilimandscharicus (Marston et al., 1988). Thesaponins from Dolichos were identified as the 3-O-β-d-glucopyranosides ofhederagenin, bayogenin and medicagenic acid (Marston et al., 1988). Saponinsfrom Mimusops elengi and M. littoralis seeds were also reported to be activeagainst Phytophthora palmivora and Colletotrichum capsici (Johri et al., 1994).The anti-infective potency of extracts from plants emphasizes the vastpotential for natural compounds to be developed into commercial products(Duke, 1990). Although many of these plant compounds have been appliedHOOOOCH 3ORH 3 COOOCH 3ORH 3 CO OOH 3 COOCompound 1 Compound 2HOHOCOOR′ROFig. 3.27. Three new glycosides with antifungal properties isolated and identifi ed fromTerminalia alata (redrawn after Srivastava et al., 2001). See text for names of compounds.