Peroxidase, polyphenoloxidase, and endopolygalacturonate transeliminase activity in different tissues of sugar beet infected with Phoma betae

Abstract

The storage rot pathogen Phoma betae normally attacks the exposed stem pith of harvested sugar beets (Beta vulgaris L.) before invading adjacent stem and taproot tissues. A comparison of rotted and sound tissues of nonselected roots showed that increased polyphenoloxidase activity occurred in rotted stem tissue, but peroxidase decreased. Endopolygalacturonate transeliminase (endoPGTE) was more active in rotted pith tissue compared with other rotted tissue. Comparison of rotted tissue from resistant and susceptible inbreds showed the greatest difference in oxidase activity occurred in resistant taproot tissue. Higher polyphenoloxidase activity was associated with resistant stem tissue of nonselected roots when catechol was the substrate rather than chlorogenic acid. Phoma betae growth in liquid culture was inhibited more by oxidation products of catechol than by those of chlorogenic acid. Peroxidase activity was associated with resistance only in stem and taproot tissue of inbreds. Endo PGTE activity was low in infected resistant tissue. When isolated cell walls of nonselected sugar beets were used as the carbon source, P. betae grew more and endo PGTE activity was greater on cell walls from pith than cell walls from adjacent stem or taproot tissue after 6 days incubation.