2012 - Washington Red Raspberry Commission

verticillium wilt is unknown, as no studies of V. dahliae on raspberry appear in the literature.
The effect of coinfection by both P. rubi and V. dahliae is also unknown. Major susceptibilities
in common cultivars may make raspberry growers more vulnerable to losses if verticillium wilt
becomes a common disease or contributes to overall decline in production regions.
Jerry Weiland is a Co-PI on this grant is a USDA researcher in Corvallis and has studied the
effects of Verticillium dahliae on red raspberry.
Relationship to WRRC Research Priority(s): This proposal addresses two first-tier priorities
of the WRRC: 1) Understanding soil ecology and soil borne pathogens and their effects on plant
health and crop yields, and 2) Development of raspberry cultivars that are disease resistant.
Objectives: This study has two objectives: 1) to assess responses to V. dahliae in existing
raspberry germplasm, and 2) to assess reaction of a subset of raspberry genotypes to combined
pressures of P. rubi and V. dahliae.
Procedures: Thirty-five raspberry genotypes representing important cultivars, breeding material,
and core R. idaeus accessions from the National Clonal Germplasm Repository (NCGR) will be
evaluated (Table 1). Some patented cultivars with high plant sales in the Pacific Northwest are
included to assess their susceptibility to verticililum wilt. ‘Wakefield’ and WSU 1507 will be
included in the screening.
Verticillium dahliae (originally isolated from red raspberry cultivar ‘Saanich’) inoculum is
produced using a method adapted from López-Escudero et al. (2007). Briefly, V. dahliae is
grown on potato dextrose agar covered with a cellophane disk. After 2 weeks, microsclerotia of
the pathogen are collected, air-dried, and mixed with sterile sand. The number of
microsclerotia/gram of inoculum is then determined and mixed into potting media at rates
suitable to obtain a density of 100 microsclerotia/gram before planting with the raspberry
genotypes. Potting media is prepared from collected field soil that was passed through a 2-mmdiam
sieve, autoclaved, and then mixed with fine vermiculite.
P. rubi (strain ATCC 16184) inoculum will be produced using a method adapted from Gigot
(2011). Briefly, P. rubi is grown on a mixture of vermiculite, V-8 broth, and oats. After four
weeks, the mixture is air-dried, then ground into a powder. Oospore density of the inoculum is
determined. Prior to planting, P. rubi inoculum is added to the potting media (above) to attain
suitable oospore densities.
The raspberry genotypes will be planted and evaluated in potting media with two treatments, 1) a
non-inoculated control and 2) inoculated with V. dahliae. A subset of eight genotypes will be
subjected to two additional treatments, 3) inoculated with P. rubi only, 4) inoculated with V.
dahliae and P. rubi. Tissue culture plants are planted into infested or control mixtures in five
replications and maintained in a greenhouse.
Plants are rated for overall appearance, shoot growth (stem length), and symptom development
(wilting and side shoot formation) at 1 month, 2 months, and 3 months after transplant. Plants
are harvested at 3 or 4 months after inoculation. A one-inch section of stem will be plated for
recovery of V. dahliae and the soil will also be evaluated for changes in V. dahliae inoculum
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