natural-products-in-plant-pest-management

Natural Products from Plants 63identified as a glycoside, 15-glucopyranosyl-glaucarubolone. Saponins fromMimusops elengi and M. littoralis seeds and crude extract of Ammi majus were86–100% effective against Phytophthora palmivora in vitro and the saponinswere 100% effective against Colletotrichum capsici (Johri et al., 1994). Encouragingresults were obtained in 2 years of field trials using these products for thecontrol of pathogens on Piper betle. No phytotoxicity was observed. Baeet al. (1997) isolated an antifungal secondary metabolite, flavonol diglycoside,from the leaves of Phytolacca Americana L. and identified the compound askaempferol-3-O-β-d-apiofwanosyl-(1,2)-β-d-lucopyranoside by spectral analyses.The compound exhibited significant antifungal activity against Botrytiscinerea, Botryosphaeria dothidea and Colletotrichum gloeosporioides (Glomerellacingulata).Earlier reports on the potential of compounds from plants to be consideredin natural product research most probably played a role in the elevationof large-scale screening programmes that followed during the past decade.For example, Pretorius et al. (2002a) performed a wide search for SouthAfrican plant species with fungitoxic properties against plant pathogens ofeconomic importance in agriculture. For this study, 39 plant species, representing20 families from the subclasses Rosidae, Asteridae, Commelinidae andLiliidae, were collected from the Blyde River Canyon Nature Reserve,Mpumalanga, South Africa. Crude extracts were prepared and bio-assayed,at equal concentrations, for their antifungal potential by determining theinhibitory effects on the mycelial growth of seven economically importantplant pathogenic fungi. Statistically, significant differences between plantsand plant parts were observed as well as the resistance of different fungi totreatment with different plant extracts. The most significant broad spectrummycelial growth inhibition was obtained with extracts from two species ofthe subclass Liliidae, namely Aristea ecklonii and Agapanthus inapertus. Thecrude extract of A. ecklonii performed best of all extracts as it totally inhibitedthe mycelial growth of all seven of the plant pathogenic test organisms andoutperformed the inhibition by a broad-spectrum synthetic fungicide( carbendazim/difenoconazole). Crude extracts of A. inapertus showed completeinhibition of four, and strong inhibition of the remaining three, plantpathogenic fungi.In the same year Pretorius et al. (2002b) also performed an in vivo studyon the control of black spot (Ascochyta blight) in pea leaves, caused byMycosphaerella pinodes, by a crude bulb extract of Eucomis autumnalis. Thefourth internode leaves were removed from 4-week-old pea (cv. Mohanderfer)plants, placed on moist filter paper in Petri dishes and inoculated with anM. pinodes spore suspension before and after treatment with the extract. Thecrude extract prevented M. pinodes spore infection of the leaves when theleaves were inoculated with spores both before and after treatment withthe extract, confirming complete inhibition of spore germination. The crudeE. autumnalis extract showed no phytotoxic effect on the leaves even at thehighest concentration applied.Equally promising was the results of a comprehensive study conductedby Chen et al. (2002) to determine the inhibitory effect of 58 plant extracts on