Dutch elm disease progression and quantitative determination of cerato-ulmin in leaves, stems and branches of elms inoculated with Ophiostoma novo-ulmi and O. ulmi.

The progression of disease and infection was monitored following inoculation of elm plants with the Dutch elm disease (DED) agentsOphiostoma novo-ulmiorOphiostoma ulmi.The disease was more severe in plants inoculated withO. novo-ulmi,with a rapid appearance of foliar symptoms just 10 days after inoculation. The degree of progression of the two pathogens in elms was similar except for the plant sections below the inoculation point, whereO. novo-ulmigrew more thanO. ulmi.Neither pathogen could be reisolated from symptomatic leaves. The concentrations of cerato-ulmin (CU) in stems, branches and leaves was quantitatively determined by enzyme-linked immunosorbent assay (ELISA). Foliar symptoms were associated with high CU contents. The contents of CU were not significantly different in branches bearing symptomless or wilted leaves. These findings support the hypothesis that CU is produced by the pathogens in xylem vessels of stems and branches, and is then translocated into leaves where it accumulates, causing DED symptoms.