Induced disease resistance in plants by chemicals

Plants can be induced locally and systemically to become more resistant to diseases through various biotic or abiotic stresses. The biological inducer s include necrotizing pathogens, non-pathogens or root colonizing bacteria. Through at network of signal pathways they induce resistance spectra and m arker proteins that are characteristic for the different plant species and activation systems. The best characterized signal pathway for systemically induced resistance is SAR (systemic acquired resistance) that is activated by localized infections with necrotizing pathogens. It is characterized by protection against a broad range of pathogens, by a set of induced proteins and by its dependence on salicylic acid (SA) Various chemicals have been d iscovered that seem to act at various points in these defense activating ne tworks and mimic all or parts of the biological activation of resistance. O f these, only few have reached commercialization. The best-studied resistan ce activator is acibenzolar-5-methyl (BION). At low rates it activates resi stance in many crops against a broad spectrum of diseases, including fungi, bacteria and viruses. In monocots, activated resistance by BION typically is very long lasting, while the lasting effect is less pronounced in dicots . BION is translocated systemically in plants and can take the place of SA in the natural SAR signal pathway, inducing the same spectrum of resistance and the same set of molecular markers. Probenazole (ORYZEMATE) is used mai nly on rice against rice blast and bacterial leaf blight. Its mode of actio n is not well understood partly because biological systems of systemically induced resistance are not well defined in rice. Treated plants clearly res pond faster and in a resistant manner to infections by the two pathogens. O ther compounds like beta-aminobutyric acid as wdl as extracts from plants a nd microorganisms have also been described as resistance inducers. For most of these, neither the mode of action nor reliable pre-challenge markers ar e known and still other pathways for resistance activation are suspected. R esistance inducing chemicals that are able to induce broad disease resistan ce offer an additional option for the farmer to complement genetic disease resistance and the use of fungicides. If integrated properly in plant healt h management programs, they can prolong the useful life of both the resista nce genes and the fungicides presently used.