Phytoanticipins: The constitutive defense compounds as potential botanical fungicides

Abstract

Present control technologies of plant pathogenic fungi decouple the pathogen's life cycle mainly in two points of ontogeny, either by destroying spores prevent the infection or inhibit the biotrophic thallus, thus anticipating the formation of new infective propagules. Although, nowadays, the only tool for credible control of cultivated plants is the use of synthetic chemicals, the calculability of yield sureness has been worldwide threatened by the emergence of acquired tolerance to this group of pesticides as well as anxious feelings for their undesirable side effects. This situation urges the development of efficient alternative control agents, as threatening the net return even 10% disease incidence can cause economic loss. One approach to discover newer antimicrobial compounds is to search for their presence in natural sources exploiting the defense strategies of plants against their pathogens. Contrary to phytoalexins that are synthesized de novo after the plant is exposed to microbial attack, i.e., being produced in response of elicitors or stressors, the phytoanticipins are not formed in the tissue or released from preexisting plant constituents. These substances are plant antibiotics presented in tissue prior to infection, serving as the basis of pest tolerance. Several thousands of such molecules of different structure have been identified; however, few of them met practical application. In this chapter, we focus on constitutive mechanisms that might be used for controlling phytopathogenic fungi with special regard to organic substances, which might serve either as botanical fungicides or as lead compounds for molecular design. Consequently, the introduction of alien phytoanticipins and precursors of phytoalexins into the proper host/parasite system can represent a prospective tool for disease management. We summarized the results and experiences of past three decades searching for candidates for biofungicides useful in pest management practices. The efficacy of over 100 plant species used as either spices or preparations in traditional medicine or culinary was demonstrated in vitro against 25 phytopathogenic fungi, and possible use of promising candidates was discussed.