2012 - Washington Red Raspberry Commission

Incidence and Detection of Verticillium dahliae in Red Raspberry Production Fields
Year Initiated___2013___ Current Year____2012____ Terminating Year___2014___
Project Description and Expected Outcomes:
Verticillium dahliae was recently isolated from wilted and dying red raspberry plants found in
several western Washington production fields. We propose to survey for the incidence of V.
dahliae in production fields to determine if the pathogen is widespread in the red raspberry
industry and to determine if the pathogen is consistently associated with fields containing wilting
and dying plants. Our survey will utilize two common methods for V. dahliae detection, a
culture-based method and a DNA-based method, to ensure robust detection and to compare
methods for detection and quantification of the pathogen. We expect to determine the incidence
of V. dahliae in red raspberry production fields and establish whether grower observations of
cane wilting and death are associated with this pathogen. We also expect to determine which
method of pathogen detection is more effective at detection and quantification of V. dahliae in
field soils and plant samples. This research directly addresses a #1 priority of the Washington
Red Raspberry commission, understanding soilborne pathogens and their effects on plant health.
Justification and Background:
Verticillium dahliae is a common soilborne pathogen in many agricultural soils and has recently
been suspected of infecting and killing red raspberry plants in the state of Washington.
Historically, relatively little research has addressed the role of V. dahliae in red raspberry
production. An early report indicated that V. dahliae killed canes and reduced yields of Rubus
idaeus cultivars in England (Harris, 1925). The pathogen was also described from Ontario,
Canada, where 5 - 20% of the plants in red raspberry fields were infected (Berkeley and Jackson,
1926). Symptoms of the disease have been described as yellowing and wilting leaves followed
by cane death. Occasionally, a blue discoloration was observed on canes, but this was not found
consistently in all infected plants. Often, the plants were not completely killed and new shoots
were able to grow from noninfected roots. But, in other cases, entire hills of red raspberry were
killed. The disease usually has a patchy distribution and severity may differ from year to year;
fields of Cuthbert that had severe Verticillium wilt one year only had a trace of disease in the
following two years (Berkeley and Jackson, 1926).
Red raspberry cultivars are often considered as resistant to Verticillium (Fiola and Swartz, 1994).
However, V. dahliae was recently found in plant and soil samples collected from declining red
raspberry fields in western Washington in 2012 by two commercial analytical laboratories and
one research laboratory (Weiland, unpublished data). In addition, two years of greenhouse
inoculations of Meeker red raspberry with V. dahliae have shown that this cultivar can be
infected and killed by the pathogen (Figure 1).
Although the pathogen has been detected from naturally-infected plants and it is known to cause
disease, additional information is needed in order to establish whether V. dahliae is a threat to
red raspberry production. First, the incidence of V. dahliae in production fields as well as the
amount of inoculum associated with disease remains unknown. A survey is needed in order to
determine: a) whether V. dahliae is widely present in the red raspberry industry; b) if its presence
is associated with the pockets of disease observed in fields in 2012; and c) to determine if
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