The Role of Stress Metabolites in Establishing Host-parasite Specificity between Sweet Potato and Ceratocystis fimbriata, Black Rot Fungus

Abstract

Differential growth of two strains of Ceratocystis fimbriata EII. and Halst. was demonstrated in liquid media containing exudates from the infected sweet potato root tissues; the germ tube growth of the taro strain, incompatible with sweet potato, was specifically inhibited in medium containing the exudate from the taro-strain-infected tissues which had been incubated for 18hr, whereas germ tube growth of the sweet potato strain, compatible with sweet potato, was not inhibited in media containing the same dilution of any exudates. Furanoterpenoid phytoalexins and umbelliferone were shown to be the main cause of differential inhibitory activity of exudates from the infected tissues. The taro strain was more sensitive than the sweet potato strain to inhibition by furanoterpenoid phytoalexins in both germination and germ tube growth. Umbelliferone inhibited germ tube growth of the taro strain only but not the seet potato strain, at the concentrations tested.
The content of umbelliferone increased before that of furanoterpenoid phytoalexins in both tissues infected by the sweet potato and taro strains. Umbelliferone accumulated to the same extent in the early stages in both tissues. On the other hand, the content of furanoterpenoid phytoalexins in the tissues infected by the taro strain started to increase earlier (12 hr) than that in the tissues infected by the sweet potato strains (18hr).