Introduction

As plants are non-motile orgnaisms and lack the sophisticated immune system that animals have, they had to develop their own defence system against pathogens and predators, and systems to lure motile creatures for fertilization and dissemination. Plants are capable of synthesizing an overwhelming variety of low-molecular-weight organic compounds, called secondary methbolities, many with very unique and complex structures. More than 100,000 different secondary metabolites have been found from plants (Buckingham, 1998; Dixon, 2001), with many more yet to be discovered; estimated of the total number in plants exceed 500,000 (Mendelsohn and Balick, 1995). Many of these compounds are differentially distributed among limited taxonomic groups within the plant kingdom and, conversely, each plant species has a distinct profile of secondary metabolites.

Many of these secondary products are bactericidal, fungicidal, repellent, or even poisonous to herbivores. Plant secondary metabolites have for thousands of years played an important role in medicine, crop disease and weed control. Nowadays, they are used either directly or after chemical modification. Examples of these compounds include flavonoids, phenols and phenolic glycosides, unsaturated lactones, sulphur compounds, saponins, cyanogenic glycosides and glucosinolates (Go'mez Garibay et al., 1990; Bennett and Wallsgrove, 1994; Grayer and Harborne, 1994).

Plant diseases cause serious losses in crop production. Pesticide application is currently the primary way to control crop disease, but it has raised an array of environmental problems. Achieving sustainable agriculture will require avoiding a

Building Your Own Greenhouse

Building Your Own Greenhouse

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