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. atr oseptica was examined. In stem tissue showing early symptoms of blackl eg, 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 stereoisom er of rishitin and solanascone were detected in smaller amounts, but n o 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 t han phytuberin concentrations. The progress of blackleg within cultiva rs was not homogenous and a correlation between the content of phytoal exins in diseased stem tissue and cultivar resistance to blackleg is u ncertain. Thin roots and stolons with young developing tubers were exc ised from field-growing plants and incubated aerobically in liquid cul tures with Erwinia. In both roots and stolons we detected rishitin (45 and 17 . 5 mu g g(-1) fresh weight, respectively), solavetivone (4 an d 2 . 5 mu g g(-1) fresh weight, respectively) and some phytuberin. In stolons, trace amounts of phytuberol and hydroxysolavetivone were fou nd. Due to tissue maceration, we could not distinguish between accumul ation in the tissue with subsequent release and active secretion into the extracellular space.