natural-products-in-plant-pest-management

Fungal Endophytes 227over 50% of the new chemical products registered by the US Food and DrugAdministration (FDA) as anticancer agents, antimigraine agents and antihypertensiveagents from 1981 to 2002 are natural products or their derivatives(Newman et al., 2003). Excluding biologics, between 1989 and 1995, 60% ofapproved drugs and pre-new-drug-application (NDA) candidates were ofnatural origin. From 1983 to 1994, over 60% of all approved and pre-NDAstage cancer drugs were of natural origin, as were 78% of all newly approvedantibacterial agents (Concepcion et al., 2001). The discovery and developmentof taxol is a modern example of a natural product that has made anenormous impact on medicine (Wani et al., 1971; Suffness, 1995; Schulz andChristine, 2005).Antibiotics from endophytic fungiGenerally, the most commonly isolated endophytic fungi are in the group ofFungi Imperfecti or Deuteromycotina. Also, it is quite common to isolateendophytes that produce no fruiting structures whatsoever such as Mycelia-Sterilia.Cryptosporiopsis cf. quercina is the imperfect stage of Pezicula cinnamomea,a fungus commonly associated with hardwood species in Europe. It was isolatedas an endophyte from Tripterigeum wilfordii, a medicinal plant native toEurasia (Strobel et al., 1999). On Petri plates, C. quercina demonstrates excellentantifungal activity against some important human fungal pathogensincluding C. albicans and Trichophyton spp. Cryptocandin, a unique peptideantimycotic related to the echinocandins and the pneumocandins (Walsh,1992), was isolated and characterized from C. quercina (Strobel et al., 1999).This compound contains a number of peculiar hydroxylated amino acidsand a novel amino acid, 3-hydroxy-4-hydroxymethyl proline (Fig. 11.2). It isgenerally true that not one but several bioactive and related compounds areproduced by an endophytic microbe. So it is that other antifungal agentsrelated to cryptocandin are also produced by C. quercina. Cryptocandin isalso active against a number of plant pathogenic fungi including S. sclerotiorumand Botrytis cinerea. Cryptocandin and its related compounds are currentlybeing considered for use against a number of fungi causing diseases ofthe skin and nails.Cryptocin, a unique tetramic acid, is also produced by C. quercina(Fig. 11.3) (Li et al., 2000). This unusual compound possesses potent activityagainst Pyricularia oryzae, the causal organism of ‘rice blast’, one of the worstplant diseases in the world, as well as a number of other plant pathogenicfungi (Li et al., 2000). The compound was generally ineffective against anarray of human and plant pathogenic fungi. Nevertheless, with minimuminhibitory concentrations against P. oryzae at 0.39 μg/ml, this compound isbeing examined as a natural chemical control agent for rice blast and is beingused as a model to synthesize other antifungal compounds.Pestelotiopsis microspora is a common rainforest endophyte (Strobel, 2002;Strobel and Daisy, 2003). It turns out that enormous biochemical diversity