Chapter 12. SEARCH FOR ANTIPHYTOPATHOGENIC COMPOUNDS INVOLVED IN PLANT DEFENCE

SGARIGLIA, M. A.; SOBERÓN, J. R.; SAMPIETRO, D. A.; QUIROGA, E. N.; VATTUONE, M. A.

Plant Bioassays

Studium Press, LLC

Lugar: Houston, USA; Año: 2009; p. 239 - 272

Phytopathogenic organisms annually cause 20 % losses in crop yields globally in billion of dollars. Most agricultural products are subjected to diseases both in field conditions and after harvest and bacteria and fungi are the major groups of pathogens involved. About 1600 bacterial species, including both Gram-negative and positive bacteria, mycoplasma-like organisms and spiroplasmas cause plant diseases. More than 8000 fungal species attack plants. Plant infections produced by yeasts are greater than those caused by filamentous fungi. However, filamentous fungi are less susceptible to commercially available antimicrobials. Pathogens are controlled through intensive use of agrochemicals, leading to the development of resistant strains, especially among phytopathogenic fungi. This reality justifies the search for natural antimicrobial agents as an alternative to the synthetic ones and promotes research of secondary compounds involved in plant-pathogen interactions. New antimicrobial leader structures with low toxicity for humans and animals, more selective against noxious organisms and relatively costless need to be discovered. Several workers have screened anti-phytopathogenic compounds from plant origin and suggest that plants are an important source of these substances. This is expectable considering that plant antimicrobials are part of natural defensive responses against phytopathogens and may be biosynthesized in a constitutive (i.e. phytoanticipins) or inducible (i.e. phytoalexins) manner. This chapter describes methods for in vitro evaluation of anti-bacterial and anti-fungal activities. Techniques and procedures described are useful tools to detect and quantify bioactivity of total extracts, purified extracts or pure compounds. The methodology employed includes diffusion methods, mainly oriented to determine the anti-microbial activity and dilution methods, which are appropriate for its quantitative analysis.