Production of cerato-ulmin in white elm following artificial inoculation with Ceratocystis ulmi

Abstract

In vivo production of cerato-ulmin (CU) in white elm was investigated following artificial inoculation with Ceratocystis ulmi. Conditions for inoculation and incubation were controlled and water extracts obtained from the infected host tissue assayed for CU by immuno-double diffusion. Detached host (white elm) branch sections were individually inoculated with C. ulmi by flushing the sections with a spore suspension; 4-day or 10-day incubation periods followed. The interim liquid was flushed out with water then concentrated and assayed for CU. Confirmation that CU was produced in the detached host following the 10-day incubation period only indicates that detectable levels of CU were produced during the prolonged incubation period. Intact host (white elm) trees were also artificially inoculated with C. ulmi by pressure injection of a spore suspension via the root system. When 50% of the crown became wilted, the brown-streaked outermost xylem wood, which comprised the major site for host-pathogen interaction, was removed and the concentrated water extract obtained from the processed wood powder was assayed for CU. It was confirmed that CU was produced in the intact host when external symptoms of wilting and internal symptoms of brown-streaking were expressed. These trials clearly support previous evidence for in vivo production of CU in white elm naturally infected with C. ulmi, and further strengthen the hypothesis that CU is involved in the development of Dutch elm disease.