Histopathology of Daucus Carota L. Root Cells Treated with Toxic Metabolites Produced by Alternaria Radicina and A. Alternata

Alternaria radicina Meier, Drechsler & Eddy [syn. Stemphylium radicinum (Meier, Drechsler et Eddy) Neerg.] is a pathogen causing a range of symptoms in carrot, including preand post-emergence dampingoff, necrosis of the crown and root, foliar, flowerand seed-stalks, and umbel and seed blight. The greatest damage occurs post-harvest, during root storage (Meier et al., 1922; Neergaard, 1945; Maude, 1966; Pryor et al., 1994, 1998; Pryor and Gilbertson, 2002). A. alternata (Fr.) Keissler is one of the most common saprotrophs or facultative parasites associated with various parts of plants (Scheffer, 1992). Up to 68% of carrot root samples collected in several European countries were found to be contaminated with the fungus (Solfrizzo et al., 2005). As much as 70% of mature carrots can be rendered unmarketable if heavily infested or infected by A. radicina and A. alternata (Solfrizzo et al., 2005). Alternaria species produce both host-specific and non-host-specific toxic secondary metabolites (Montemurro and Visconti, 1992; Visconti et al., 1992; Bottalico and Logrieco, 1998; Solfrizzo et al., 2004b). A. radicina was capable of producing primarily radicinin (RAD, syn. stemphylone) followed by radicinols (ROHs), i.e. radicinol (ROH) and epiradicinol (epi-ROH) when grown on carrot root discs. The latter have also been found in carrot roots either naturally contaminated or inoculated with