EXTRACELLULAR PROTEIN ELICITORS FROM PHYTOPHTHORA - HOST-SPECIFICITY AND INDUCTION OF RESISTANCE TO BACTERIAL AND FUNGAL PHYTOPATHOGENS

Purified elicitor proteins (elicitins) from Phytophthora parasitica and P. cryptogea induced both localized and distal hypersensitive responses (HR) specifically in Nicotiana species and some radish and turnip cultivars but not in 12 other plant species. Differences between HR induction by acidic (parasiticein) and basic (cryptogein) isoforms were observed only for distal HR assays. Cryptogein consistently induced stronger distal necrosis in tobacco and radish than parasiticein. Similar results were obtained for the induction of a bean chalcone synthase promoter fused to a beta-glucuronidase reporter in a transgenic tobacco line. However, in localized infiltration assays, both elicitin isoforms induced necrotic HR lesions at similar levels, suggesting that the difference between acidic and basic elicitins is related to distal HR induction and not to necrogenicity per se. Induced resistance to two P. parasitica isolates was observed on tobacco after pretreatment with elicitins. In radish, elicitins induced cultivar-specific HR and resistance to the bacterial pathogen, Xanthomonas campestris pv. armoraciae.