|SIKDAR, PARAMA - Washington State University
|WILLETT, MIKE - Washington Tree Fruit Research Commission
Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2017
Publication Date: 3/21/2018
Citation: Sikdar, P., Willett, M., Mazzola, M. 2018. Pruning of Manchurian crabapple for management of speck rot and Sphaeropsis rot in apple. HortScience. 53:329-333.
Interpretive Summary: Plant pests and pathogens have significant potential to limit the export of agricultural commodities around the globe and thus reduce the economic vitality of agricultural industries. Two fungal pathogens, Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens, incite the post-harvest diseases of apple speck rot and Sphaeropsis rot, respectively. Fruit infested with these pathogens were detected in shipments resulting in the closure of specific export markets from 2012-2014. Studies were conducted to develop protocols that could be implemented in production systems that would minimize fruit infection in the orchard and thus limit the possibility of disease development in fruit destined for export markets. Crabapple pollinators commonly used in Pacific Northwest orchards were previously shown to be the dominant source of inoculum for these fungal pathoges. Therefore, a systems approach was examined that focused on reducing pathogen inoculum on these susceptible plants in concert with post-harvest preventative treatments. This approach involved pruning of crabapple during flower bloom to remove plant material that might be infected with the pathogen and thus minimize the level of inoculum in the orchard with potential to cause infection of apple fruit. This treatment was utilized with or without a post-harvest fungicide application of apple fruit prior to placement in cold storage. The pruning alone treatment was shown to be just as effective as the systems treatment for reducing apple fruit infection. Implementation of this knowledge in the orchard will help ensure continued access by the Pacific Northwest tree fruit industry to highly desirable export markets.
Technical Abstract: Phacidiopycnis washingtonensis and Sphaeropsis pyriputrescens are two important quarantined fungal pathogens that cause post-harvest speck rot and Sphaeropsis rot, respectively, in apple. Due to detection of these pathogens in fruit shipments and quarantine regulation, export of apple from Washington State to China was banned between 2012 and 2014. From previous study it was established that pycnidia of P. washingtonensis and S. pyriputrscens survive in twig cankers on Manchurian crabapple which serves as a dominant pollinizer in the Washington State apple industry. These pycnida serve as a primary source of inoculum for subsequent infection of apple fruit in the orchard. Studies were conducted at multiple locations in Washington State to determine the efficacy of implementing pollinizer pruning as a method to control fruit infection in the orchard and subsequent development of speck rot and Sphaeropsis rot in storage. Experimental treatments included pruning Manchurian crabapple at flower bloom followed by fungicide treatment at harvest, pruning only without fungicide application and control treatment with no pruning or fungicide. Fruit were harvested at the commercial harvest dates, stored in regular atmosphere at 0°C and disease development monitored over an 8 month post-harvest period. The pruning/at harvest fungicide treatment (systems approach) significantly reduced the incidence of postharvest speck rot and Sphaeropsis rot in storage during the initial experimental field season. During year two, both the pruning alone and systems approach, controlled post-harvest fruit rot and there was no significant difference between the two treatments. Findings from this study will be instrumental for control of these post-harvest diseases and maintenance of international market access for fruit from the Pacific Northwest.