ELICITATION AND ACCUMULATION OF PHYTOALEXINS IN STEMS, STOLONS AND ROOTS OF ERWINIA-INFECTED POTATO PLANTS

The accumulation of sesquiterpenoid stress metabolites in potato stems, roots and stolons after inoculation with Erwinia carotovora ssp. atroseptica was examined. In stem tissue showing early symptoms of blackleg, high concentrations of sesquiterpenoid phytoalexins, up to 560 mu g of solavetivone and 470 mu g of rishitin per gram fresh weight, had accumulated. Phytuberin, phytuberol, hydroxysolavetivone, a stereoisomer of rishitin and solanascone were detected in smaller amounts, but no lubimin, a main phytoalexin of Phytophthora-infected potato tubers, was found. In stem tissue, solavetivone concentrations were often much higher than rishitin concentrations, and always several fold higher than phytuberin concentrations. The progress of blackleg within cultivars was not homogenous and a correlation between the content of phytoalexins in diseased stem tissue and cultivar resistance to blackleg is uncertain. Thin roots and stolons with young developing tubers were excised from field-growing plants and incubated aerobically in liquid cultures with Erwinia. In both roots and stolons we detected rishitin (45 and 17 . 5 mu g g(-1) fresh weight, respectively), solavetivone (4 and 2 . 5 mu g g(-1) fresh weight, respectively) and some phytuberin. In stolons, trace amounts of phytuberol and hydroxysolavetivone were found. Due to tissue maceration, we could not distinguish between accumulation in the tissue with subsequent release and active secretion into the extracellular space.