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Two-year screenhouse studies evaluating blueberry genotypes for mummy berry resistance

Volume 12 Issue 12

Purnima Puri1, Lisa Wasko DeVetter1, Chakradhar Mattupalli1

1WSU Mount Vernon Northwestern Washington Research and Extension Center, Mount Vernon, WA 98273

[Funding for this research was provided by the Washington Blueberry Commission. Blueberry plants were generously donated by the USDA-ARS blueberry breeding program, Fall Creek Farm and Nursery, Inc. (Lowell, OR), and Driscoll’s (Watsonville, CA)]



As the Washington State and greater Pacific Northwest (PNW) blueberry industry expands, there is a need to test new cultivars and advanced selections generated by public and private breeders in the PNW for disease susceptibility under different environmental conditions. Here, we report screening of select blueberry genotypes for their response to mummy berry (causal agent: Monilinia vaccinii-corymbosi) disease, which negatively impacts profitable production of blueberries in the PNW. The disease results in blighting of young vegetative and floral tissues as well as mummification of berries.



Assess susceptibility of select blueberry genotypes to mummy berry fruit rot.


  • During the two-year study period (2022-23), five plants of 11 blueberry genotypes (‘Aurora’, ‘Bluejay’, ‘Calypso’, ‘Duke’, ‘Liberty’, ‘Northland’, DSA4, ORUS264-1, ORUS292-2, ORUS587-1, and ORUS620-2) in plastic containers were grown inside a screenhouse at the WSU Mount Vernon Northwestern Washington Research and Extension Center. DSA4 was not tested in 2022, and ‘Liberty’ was excluded in 2023.
  • Inoculum was prepared by dislodging conidia from blighted leaf tissues collected from a mummy berry infested field. Using a paint brush, the inoculum (5.75 x 105 conidia/ml) was applied to the stigma of open flowers. Following inoculation, freshly collected pollen from different genotypes was applied to the stigma of the flower using a paintbrush to ensure proper fruit development. Unopened flowers were removed from the flower cluster before covering the inoculated branches with paper bags overnight to maintain consistent humidity for conidial germination (Fig. 1).
  • Inoculations were carried out thrice in May 2022 and twice in May 2023 coinciding with the development of new flowers. Each plant was inoculated at least once.
  • Green fruits that developed from inoculated flower clusters were collected in early July (2022) or during the last week of June (2023), and then cut transversely to see the characteristic masses of white fungal growth (Fig. 2).
  • Mummy berry fruit rot incidence was calculated based on the number of infected green fruits and the total number of harvested green fruits from each plant.

Figure 1. Blueberry plants growing in a screenhouse at WSU Mount Vernon Northwestern Washington Research and Extension Center, Washington

Figure 2. Infected blueberry with white mycelia of Monilinia vaccinii-corymbosi (top). A healthy and normally developing green blueberry (bottom).


  • A non-parametric test was conducted to analyze the data. As the effect of year was not significant (P = 0.06), data were combined from both years to determine the effect of genotype on mummy berry fruit rot.
  • Significant differences were observed among genotypes for mummy berry fruit rot incidence. ‘Northland’ had the lowest disease incidence differing significantly from ORUS587-1, ‘Liberty’, ORUS620-2, ORUS264-1, and ‘Aurora’ (Fig. 3). The cultivar ‘Duke’ differs significantly with ORUS587-1 and ‘Liberty’. It is to be noted that data from ‘Liberty’ plants were obtained only in 2022 but not in 2023.


Figure 3. Bar graph showing mummy berry fruit rot incidence among 11 blueberry genotypes. Genotypes sharing the same lowercase letters are not significantly different from each other (P < 0.05) and standard error bars are depicted. DSA4 was not tested in 2022, and ‘Liberty’ was excluded in 2023.

Conclusion and future work:

  • According to the PNW Plant Disease Management Handbook, ‘Bluejay’ is considered resistant to intermediate, and ‘Northland’ is susceptible to moderately resistant to secondary infections (conidial infection of blueberry flowers) that result in fruit mummification. The results of this two-year study indicate ‘Bluejay’ to be intermediate and ‘Northland’ to be resistant to secondary infections.
  • Similar to year one, differential responses among the tested genotypes were observed for mummy berry fruit rot incidence proving the current experimental procedures to be useful for continued genotypic screening for resistance or low susceptibility to mummy berry fruit rot.
  • Future experiments will include screening additional genotypes received from USDA-ARS and nursery cooperators.