Evaluation location: Oregon, United States
The objective of this study was to evaluate 29 diverse octoploid and 1 decaploid strawberries for soilborne pathogen mortality.
Germplasm. The NCGR in Corvallis, OR provided 30 accessions from the Fragaria Supercore including 15 F. chiloensis accessions, 14 F. virginiana accessions, and one F. cascadensis accession. A total of 21 F. ×ananassa accessions were also evaluated. These accessions consisted of 10 selections and cultivars from the MSU strawberry breeding program in East Lansing, MI and 11 from the HCRU breeding program in Corvallis, OR. The public cultivars Monterey, Portola, and Albion were used as susceptible controls for Fusarium, Verticillium, and Macrophomina, respectively. Plant propagation was conducted to produce daughter plants for replicated inoculation trials for the Supercore and F. ×ananassa accessions. Runners for the F. ×ananassa accessions were produced by the University of California, Davis in a high elevation nursery in Dorris, CA and sent to the California Polytechnic State University (Cal Poly) in San Luis Obispo, CA.
Runners for the Supercore accessions were produced at Cal Poly. The Supercore mother plants were maintained in 7.6-L containers and fertilized with slow-release Osmocote Plus (15N-3.9P-4.8K). Plants were irrigated as needed throughout the trial using a showertype sprayer nozzle directed at the base of the crown. To establish daughter plants for inoculation, runners of each accession were rooted in plug cells (L × W × D of 8.00 cm × 3.94 cm × 5.92 cm; Greenhouse Megastore, Sacramento, CA) containing a substrate consisting of 33% coconut coir, 33% sphagnum peat moss, and 33% perlite. The runners were kept under intermittent mist for seven to 10 days until roots colonized the substrate.
Once rooted, plants were allowed to grow for another four to six weeks before host resistance screens were initiated.
Phenotyping.Trials were conducted in the strawberry greenhouse at the Cal Poly Crops Unit. Host resistance screens were conducted for each of the three pathogens (F. oxysporum f. sp. fragariae, V. dahliae, and M. phaseolina). Seven plants of each selection were used per pathogen screen, inoculating six and leaving one as a non-inoculated control. Local isolates of each pathogen originating from diseased strawberry crowns were used for each inoculation. Inoculum for each trial consisted of 1 × 106 conidia per mL of water for F. oxysporum f. sp. fragariae (isolate GLI080), 5 × 106 conidia per mL of water for V. dahliae (isolates Vd1, Vd3, Vd7, and Vd20), or a slurry of M. phaseolina microsclerotia at 2,500 colony-forming-units per mL of slurry (isolates Mp8, Mp21, and Mp22). Plants were inoculated by soaking the roots in the inoculum for 5 min.
The noninoculated controls were soaked in water for 5 min. Plants were then transplanted into 0.5 L pots (10.2 cm diameter) with the same potting mix as previously described and arrayed randomly on a greenhouse bench. Plant mortality was assessed after the susceptible control cultivars had a mortality of greater than 83.3 % for their respective diseases. Susceptible control cultivars were evaluated only in trials in which they were the susceptible control. Fusarium and Verticillium trials were conducted twice for all accessions. Macrophomina trials were conducted once for Supercore accessions and twice for breeding accessions. Average percent mortality was calculated and accessions with less than 33.3 % mortality were considered resistant.