2019 ASHS Annual Conference

Cane dieback and foliar necrosis caused by an unknown pathogen have been observed in elderberry (Sambucus nigra subspecies) plantings in early spring. Studies were conducted to identify the causal organism and determine the effect of infection on vegetative growth and fruiting of selected elderberry cultivars. A Phoma sp. was isolated from symptomatic ‘Ranch’ elderberry canes growing in a commercial planting in Missouri. All canes of one year-old ‘Bob Gordon’ potted plants inoculated on 10 Mar. with the Phoma isolate were symptomatic by 14 days after treatment (DAT). By 150 DAT, cane length of Phoma sp.-inoculated ‘Bob Gordon’ plants was reduced by 65% when compared with the non-inoculated controls. By the end of the growing season, Phoma sp.-inoculated canes never flowered or produced fruit. However, each non-inoculated cane developed an inflorescence and produced fruit, averaging 29 g/umbel. When elderberry plants were inoculated on 4 June in a similar experiment, cane length and leaf and leaflet numbers of inoculated ‘Bob Gordon’ plants were less than non-inoculated controls at 14, 30, and 60 DAT when the study was terminated. The fungus was tentatively identified as P. novae-verbascicola based on analysis of genomic DNA from the internal transcribed space region. Thus, the newly reported cane dieback disease, caused by Phoma sp., adversely affected plant growth and fruiting of ‘Bob Gordon’ elderberry.