natural-products-in-plant-pest-management

Proteinaceous and Polyketide Compounds in Plant Protection 127than fungicidal activity contributes to the protective effect of statins( Dzhavakhiya and Petelina, 2008).The resistance of fungi to extreme environmental conditions and bioticstresses is largely determined by their ability to produce protective highmolecular-weightpigments. One of the common fungal pigments in cell walls ismelanin. Melanin is a coloured polymer produced by many plant pathogenicfungi, including M. grisea, S. nodorum, C. lagenarium and C. atramentarium,through the pentaketide pathway and depends on the availability of acetyl-CoA. Melanin plays a significant role in the infectivity of these fungi. Forinstance, the ability of the rice pathogen M. grisea to penetrate into tissues of thehost plant is directly associated with the presence of melanin in the fungus.Strains of M. grisea and C. lagenarium defective in melanin formation lose pathogenicityand are incapable of forming mycelial overgrowth in host plants. Revertantsrestoring wild-colour type regain pathogenicity (Dzhavakhiya et al., 1990).Interestingly, antimelanogenic compounds, aminoalkylphosphinates, afamily of phospho-analogues of natural amino acids, suppress biosynthesisof melanin and some toxic metabolites in the polyketide pathway of M. grisea,and are also fungicidal. The aminoalkylphosphinates serve as analogues ofalanine, a precursor to pyruvic acid that is required for melanin biosynthesis.Exposure of fungi to the phospho-analogues of amino acids inactivates pyruvatedehydrogenase, thus inhibiting synthesis of acetyl-CoA and melanin(Zhukov et al., 2004) as well as aflatoxins (Khomutov, Khurs, Shcherbakova,Mikityuk, Dzavakhiya and Zhemchuzhina; unpublished data). The discoverythat non-fungicidal lovastatin and compactin concentrations can inducemycelium de-pigmentation and decrease disease severity on plants suggeststhat their protective effect may be associated with impairing pathogenicitydue to an effect on melanin biosynthesis in causative agents. Statins and fungalmelanin are both polyketides. Thus, the metabolism of the two compoundsis interrelated, and it is not improbable that statins can negativelymediate a stage of the polyketide pathway involved in the melanization ofplant pathogenic fungi.Although the mode of protective action of statin is required for understandingand further research, first small-plot field trials suggest they may beof certain interest from a practical point of view. For example, one preplantingtreatment of potato tubers by soaking in 0.1% compactin solution forhalf an hour resulted in a 1-month delay of late blight (P. infestans) emergenceon plants and a slower course of disease. Only extremely high statin concentrationsof 0.5% undesirably influenced plant physiological characteristics. Bythe end of the growing season, an insignificant reduction of potato late blightwas observed on plants arising from the treated tubers, but these plantsproduced fewer diseased tubers. There is reason to suppose that lovastatinand compactin possess anti-phytoviral activity (Ukraintseva, 2008).Further research of the mechanisms responsible for protective activitycould help statins take a fitting place among the biopesticides of tomorrow.Lovastatin and compactin per se might serve as base molecules for biochemicalengineering of active analogues, and the approaches used to studyingtheir plant-protecting properties might be implicated in screening of other