|YEO, JOHN - Oregon State University|
|SULLIVAN, DAN - Oregon State University|
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/30/2015
Publication Date: 2/5/2016
Citation: Yeo, J.R., Weiland, G.E., Sullivan, D., Bryla, D.R. 2016. Susceptibility of highbush blueberry cultivars to Phytophthora root rot. HortScience. 51(1):74-78.
Interpretive Summary: Phytophthora cinnamomi is an important soilborne pathogen causing Phytophthora root rot of blueberry. To identify plants with resistance to this pathogen, twenty one cultivars were screened for resistance to this disease in two greenhouse experiments: 11 cultivars are commonly grown for commercial production, seven are newly-released cultivars, and three are advanced selections from a blueberry breeding program. Plants of each cultivar were inoculated with P. cinnamomi and compared to healthy plants grown without inoculation. Resistant cultivars were identified as those that exhibited good shoot and root growth despite inoculation with the pathogen, whereas susceptible cultivars exhibited poor shoot and root growth when inoculated with the pathogen. Four common cultivars, ‘Legacy’, ‘Liberty’, ‘Aurora’, and ‘Reka’, and two newly-released cultivars, ‘Overtime’ and ‘Clockwork’ were the most resistant. Two advanced selections were also identified as resistant and will be released as new cultivars in the future. The most susceptible cultivars were three common cultivars, ‘Duke’, ‘Draper’, and ‘Bluetta’ and five newly-released cultivars, ‘Blue Ribbon’, ‘Top Shelf’, ‘Last Call’, ‘Cargo’, and ‘Ventura’. These latter cultivars should not be planted in poorly drained sites, in clay soils, or in sites where P. cinnamomi is known to occur.
Technical Abstract: Phytophthora cinnamomi Rands is a ubiquitous soilborne pathogen associated with root rot in many woody perennial plant species, including highbush blueberry (Vaccinium sp.). To identify genotypes with resistance to the pathogen, cultivars and advanced selections of highbush blueberry were grown in a greenhouse and either inoculated or not with propagules of P. cinnamomi. Two experiments were conducted, including one with 10 cultivars commonly used for commercial production, and another with seven newly-released cultivars, three common cultivars, and three advanced selections of highbush blueberry. Pathogen resistance was based on the shoot and root dry biomass of the inoculated plants relative to the non-inoculated plants within each genotype, as well as on the percentage of root infection among the genotypes. The most resistant genotypes included four common cultivars, ‘Legacy’, ‘Liberty’, ‘Aurora’, and ‘Reka’, two new cultivars, ‘Overtime’ and ‘Clockwork’, and two advanced selections, an early-season and a late-season type, which are both slated for release as new cultivars. When these genotypes were inoculated, relative shoot biomass ranged from 57% to 101% of the non-inoculated plants, while relative root biomass ranged from 24% to 71%. Relative shoot biomass of the most susceptible genotypes, on the other hand, ranged from 19% to 53%, and relative root biomass ranged from only 11% to 26%. The most susceptible genotypes included three common cultivars, ‘Duke’, ‘Draper’, and ‘Bluetta’, and five new cultivars, ‘Blue Ribbon’, ‘Top Shelf’, ‘Last Call’, ‘Cargo’, and ‘Ventura’. These latter cultivars are not recommended at sites with conditions conducive to root rot, such as those with clay soils and poor drainage.