The induced increase in respiratory rate as well as other metabolic activities in diseased plant tissues has been an object of extensive studies to elucidate mechanisms involved in host-parasite relationship1'2>. in a system of sweet potato root and the black rot fungus, Ceratocystis fimbriata, the characteristics of biochemical patterns which take place in the host tissue after the infection are a remarkable increase in a number of enzyme activity and an accumulation of some metabolites such

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... phenylpropanoids and furanoterpenoids3'4'. Uritani et al.5's~ have suggested that those metabolic alterations are closely related to defence mechanisms of the host tissue against pathogenic invasion; cellular stimulation of the host tissue due to incompatibility between the host cells and the pathogenic ones induces the metabolic alteration leading to active formation of some metabolites. Several results which support the above view were reported; rate of ipomeamarone4~ or chlorogenic acid7'8 formation by resistant varieties is larger than that by susceptible varieties. Increase in respiratory rate by the infection may result from the formation of uncoupling agents in the tissue and/or leveling up of ADP concentration caused by an enhancement of ATP utilizing system as evidenced by accumulation of proteins or metabolites of low molecular weight9"0>. Predominant mode of carbohydrate breakdown involved in the induced respiration shifts from the pentose phosphate pathway at an early stage of the infection process to Embden-Meyerhof-Parnas pathway at a later stage's. Those results well coincide with massive synthesis of phenylpropanoids and f uranoterpenoids 2 days after the infection. Since the incompatibility between the host and the pathogen is directly related to the resistance of the host, if the incompatibility provides a trigger of the metabolic alteration, variations in the resistance of the host may reflect to the patterns of the induced respiration. In an attempt to elucidate the relationship between the host resistance and the induced respiration, the detailed patterns of the respiratory induction by sweet potato roots of the different resistance were investigated.