Timing of apple fruit infection by Neofabraea perennans and Neofabraea kienholzii in relation to bull’s-eye rot development in stored apple fruit

Authors: AGUILAR, C - Washington State University; Mazzola, Mark; Xiao, Chang-Lin

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/14/2016
Publication Date: 2/17/2017
Citation: Aguilar, C.G., Mazzola, M., Xiao, C. 2017. Timing of apple fruit infection by Neofabraea perennans and Neofabraea kienholzii in relation to bull’s-eye rot development in stored apple fruit. Plant Disease. 101:800-806. doi: 10.1094/PDIS-11-16-1637-RE.
DOI: https://doi.org/10.1094/PDIS-11-16-1637-RE

Interpretive Summary: Bull’s-eye rot is a disease of apple and other pome fruit caused by the fungi Neofabraea kienholzii, Neofabraea malicorticis, Neofabraea perennans and Neofabraea vagabunda. While fruit infection occurs in the orchard, disease symptoms on the fruit are not apparent at the time of harvest. A large volume of apple fruit produced in Washington State is placed in cold storage post-harvest enabling fruit availability throughout the year. During this storage season, disease symptoms including target-like brown lesions may first become apparent on the fruit surface after approximately three months of storage. The lack of disease symptoms at harvest, coupled with the slow progression of disease in cold storage translates into a very expensive disease for growers and fruit packers to manage. Difficulty is enhanced by the fact that bull’s-eye rot is a quarantine issue for export to certain international markets. In an effort to determine when fruit are most susceptible to infection by N. kienholzii and N. perennans, apple fruit of the cultivars ‘Red Delicious’ and ‘Fuji’ were inoculated in the orchard at different periods during the fruit growing season. After harvest, fruit were kept in cold storage for up to ten months, during which bull’s-eye rot disease ratings were conducted. The results from this study indicate fruit infection by Neofabraea spp. is possible throughout the entire growing season, but is most likely to occur within the final eight weeks leading up to fruit harvest.

Technical Abstract: Bull’s-eye rot is an important postharvest disease of pome fruit in the U.S. Pacific Northwest. The disease is caused by a fungal complex consisting of Neofabraea vagabunda, Neofabraea kienholzii, Neofabraea malicorticis and Neofabraea perennans. In addition to causing fruit decay, some of these fungi are also capable of causing canker diseases of pome fruit trees, which serve as the overwintering site of the pathogen and source of inoculum during the following fruit-growing season. Fruit infection by these pathogens is initiated in the orchard during the fruit-growing season but are latent at harvest. For fruit held in postharvest cold storage, bull’s-eye rot symptom development is slow to progress, requiring at least three months before symptoms are first visible. In order to determine the timing of pre-harvest fruit infection in relation to bull’s-eye rot development in cold storage, apple fruit of cultivars ‘Red Delicious’ and ‘Fuji’ were inoculated with a conidial suspension of N. perennans or N. kienholzii at multiple inoculation timings throughout the fruit growing seasons of 2012-2014. Fruit were harvested and kept in storage at 0°C for up to ten months during which time disease incidence was recorded periodically. Results from this study demonstrate that apple fruit infection by either pathogen may occur at any point during the growing season. However, infections occurring over the eight week period immediately prior to harvest yield a higher incidence of bull’s-eye rot in stored fruit compared to infections initiated earlier in the growing season. Information from this study can be utilized to assist growers within the Pacific Northwest in timing chemical application to control this disease.