Timing of perennial canker development in apple trees caused by Neofabraea perennans and Neofabraea kienholzii

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

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/27/2018
Publication Date: 1/21/2019
Citation: Aguilar, C., Mazzola, M., Xiao, C. 2019. Timing of perennial canker development in apple trees caused by Neofabraea perennans and Neofabraea kienholzii. Plant Disease. 103(3):555-562. https://doi.org/10.1094/PDIS-06-18-0935-RE.
DOI: https://doi.org/10.1094/PDIS-06-18-0935-RE

Interpretive Summary: Bull’s-eye rot is a post-harvest disease of apple and other pome fruit caused by the fungi Neofabraea kienholzii, Neofabraea malicorticis, Neofabraea perennans and Phlyctema vagabunda. These diseases cause significant losses in the Washington State tree fruit industry as symptom development and disease progression occur during the fruit storage period prior to shipment for sale. These fungi also incite a canker disease on trees in the orchard, which ultimately serve as the source of fungal inoculum for inciting infections of fruit. Neofabraea kienholzii was recently identified as participating in the bull’s-eye rot disease complex of apple. However, little is known as to the relative disease-causing potential of this fungus or the progression of disease in the orchard resulting from infection by N. kienholzii. Results from this study demonstrated that N. kienholzii shared similar trends in disease development and disease progression in the orchard with that incited by N. perennans. It was demonstrated that both pathogens can survive in the orchard year-round, and that the primary infection periods and the timing of canker development on tree limbs was comparable for both pathogens. This information demonstrates that effective disease management can be obtained for both of these fungal pathogens through use of a similar approach rather than the need to develop species-specific methods to obtain overall control of Bull’s-eye rot.

Technical Abstract: Members of the genera Neofabraea and Phlyctema have been reported to incite canker diseases of apple trees and a postharvest decay of apple fruit referred to as bull’s-eye rot. Neofabraea kienholzii was recently identified as participating in the bull’s-eye rot disease complex of apple and other pome fruit. In this study, apple twigs inoculated with N. kienholzii were shown to develop symptoms of a canker disease closely resembling perennial canker of pome fruit trees caused by N. perennans. Cankers resulting from infection by either Neofabraea spp. were more likely to be induced when twig inoculations occurred in October, and to a lesser degree in April, compared to all other inoculation timings evaluated in this study. While N. kienholzii tended to induce cankers that were smaller in size compared to N. perennans, both pathogens shared similar seasonal trends in the initiation and expansion of tree cankers. N. perennans and N. kienholzii were recovered from inoculated twigs six months post inoculation regardless of when inoculations were conducted, indicating that both pathogens can survive on diseased twigs year-round. Furthermore, acervuli were observed more often on twigs inoculated in September and April compared to those inoculated in other months. Data from this work should help further our understanding of the epidemiology of N. kienholzii, and can help growers identify important times to scout for canker disease in their orchards.