Ethylene Production in Sweet Potato Root Tissue Infected by <italic>Ceratocystis fimbriata</italic>

Abstract

The rate of ethylene production by sweet potato (Ipomoea batatas Lam. cv. Norin No. 1) root tissue infected with Ceratocystis fimbriata Ell. & Halst. increased markedly during incubation at 29°C under high relative humidity. During incubation the fungus progressively invaded root tissue. The rate of ethylene production reached a peak two days after inoculation when the browning region that contained the penetrating mycelia had expanded inward about 0.3 mm from the surface, followed by a decline in ethylene production. Apparently, the 1-aminocyclopropane-1-carboxylic acid (ACC) synthase activity was not high enough, and the amount of ACC in the infected tissue was too low to account for the high rate of ethylene production throughout the incubation period. Ethylene production by the infected tissue showed scarcely any inhibition by amino-ethoxyvinylglycine, a specific inhibitor of ACC synthase. These findings suggest that the pathway of ethylene biosynthesis that operates in infected sweet potato root tissue may differ from the methionine pathway in which ACC serves as an intermediate.