Selective Elicitation of the Phytoalexin Rutalexin in Rutabaga and Turnip Roots by a Biotrophic Plant Pathogen

Stress responses of roots of rutabaga ( Brassica napus ssp. napobrassica) and turnip ( B. rapa ssp. rapa) were analyzed. Phytoalexin production due to biotic elicitation by the biotroph Albugo candida and abiotic elicitation using UV irradiation was quantified by HPLC. The phytoalexin rutalexin was produced in substantially higher amounts in rutabaga and turnip roots inoculated with A. candida than in UV irradiated roots. By contrast, production of the phytoalexins brassinin in rutabaga and cyclobrassinin in turnip was higher in UV irradiated roots than in roots inoculated with A. candida. Overall, the results suggest that A. candida is able to redirect the phytoalexin biosynthetic pathway towards rutalexin, a phytoalexin substantially less inhibitory than either brassinin or cyclobrassinin.