natural-products-in-plant-pest-management

80 J.C. Pretorius and E. van der Wattconsensus amongst scientists that research in this regard should concentrateon both the inhibitory and stimulatory effect of plant extracts on seed germination,seedling growth and the physiology of other test plants in order toverify the action at hand (Khan et al., 2001; Ameena and George, 2002; Cruzet al., 2002b; Duary, 2002; Obaid and Qasem, 2002).Probably the most effective compounds to enhance crop yield, crop efficiencyand seed vigour have been identified as brassinosteroids (BRs;Mandava, 1979; 1988), first extracted from rape (Brassica napus L.) pollen(Adam and Marquard, 1986). In a recent mini-report, Zullo and Adam (2002)confirmed the prospective agricultural uses of BRs. The assumption of theirapplication potential was made from data collected over the past threedecades and only a few examples are presented here. Yield increases thatwere in most instances significant were reported, as cited by Zullo and Adam(2002), in beans and lettuce (Meudt et al., 1983), rice (Lim, 1987), maize (Limand Han, 1988), wheat (Takematsu et al., 1988), chickpea (Ramos, 1995) andtomato (Mori et al., 1986). Many other examples of BR use for increasing cropyield can be found in the literature (Kamuro and Takatsuto, 1999; Khripachet al., 1999; Khripach et al., 2000).Besides their yield-improving effects, BRs have been shown to increaseplant growth in crops (Rao et al., 2002) and especially root growth (Müssiget al., 2003), to increase resistance in crops towards low-temperature injury(Kamuro and Takatsuto, 1999) and to increase resistance of potato to infectionsby Phytophthora infestans and Fusarium sulfureum (Kazakova et al., 1991).Although many BRs, such as 24-epibrassinolide, are commercially availableand employed in some countries, more accurate studies on dosage, methodand time of application, its suitability for the plant or cultivar, and associationwith other phytohormones are needed, because many of the results wereobtained by experiments performed in greenhouses or small fields (Zulloand Adam, 2002).A report on a prototype bio-stimulatory natural product developed froma BR-containing extract of Lychnis viscaria came from Roth et al. (2000). In2003, after 12 years of intensive research under laboratory, greenhouse andfield conditions at the University of the Free State, South Africa, a productwas listed in Germany as a plant-strengthening agent under the trade nameComCat and commercialized by a German company, Agraforum AG.Foliar applications of ComCat have been demonstrated to enhance consistentlyroot development in seedlings and final yields in a number of vegetable,fruit and row crops, as well as to induce resistance in crops towardsabiotic and biotic stress conditions, and the mechanisms of action were elucidatedon both a metabolic and genetic level (unpublished results, Pretorius,J.C. and van der Watt, E., University of the Free State, South Africa). Recently,significant yield increases in tomato, preharvest treated with ComCat,were reported by Workneh et al. (2009). The authors also claimed more than70% shelf life extension and higher marketability in tomato fruit harvestedfrom plants treated with ComCat during the vegetative growth phase comparedto the untreated control under ambient storage conditions. PreharvestComCat treated tomatoes contained lower total soluble sugar levels at