Location: Plant Genetic Resources Unit (PGRU)Title: Phenotypic evaluation of fire blight outbreak in the USDA Malus collection
|WALLIS, ANNA - Cornell University|
|COX, KARIK - Cornell University|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/10/2021
Publication Date: 1/14/2021
Publication URL: https://handle.nal.usda.gov/10113/7243708
Citation: Dougherty, L.E., Wallis, A., Cox, K., Zhong, G., Gutierrez, B.L. 2021. Phenotypic evaluation of fire blight outbreak in the USDA Malus collection. Agronomy Journal. https://doi.org/10.3390/agronomy11010144.
Interpretive Summary: Fire blight is one of the most important diseases of apple. Fire blight can spread rapidly throughout an orchard and severely impact trees within a growing season without management. During the 2020 growing season there was an outbreak of fire blight in the USDA Apple collection, maintained in Geneva, NY. Fire blight is caused by the bacteria Erwinia amylovora, and trees are typically treated with the antibiotic streptomycin during flowering season. However, after observing mild to severe fire blight symptoms throughout the collection, we identified a streptomycin-resistant strain of E. amylovora. The USDA Apple collection maintains an orchard of over 6,000 unique apple cultivars and their wild crabapple relatives. Apples vary in their response to E. amylovora ranging from highly susceptible to disease resistant, and we observed a broad phenotypic response to the 2020 outbreak. Typically, fire blight evaluations are conducted as controlled experiments or as natural observations across multiple seasons using a narrow set of cultivars. However, this outbreak allowed us to evaluate fire blight resistance on a broad range of cultivars and wild apples under common conditions. The data collected will be useful for breeding and research of disease resistance in apple, as well as inform our orchard management.
Technical Abstract: Fire blight, caused by pathogen Erwinia amylovora, is a major disease in Malus. Biological, chemical and cultural controls are efficient to manage fire blight, while rootstocks, and host resistance can limit damages. During the 2020 season a naturally occurring fire blight outbreak occurred in the USDA Malus collection, providing a unique opportunity to evaluate the diverse collection for fire blight susceptibility. The E. amylovora strain in the collection was identified as a streptomycin resistant and characterized as CRISPR spacer array profile, 41:23:38. Fire blight severity was assessed using two approaches: 1). average severity percentage, where the number of infected shoots was divided by the total number of shoots for the east and west facing sides of the tree, and 2). cut severity rating, where the trees were visually assessed after fire blight removal for amount of tree removed. Overall, 1,143 trees of 41 Malus species were assessed for average severity and 2525 trees of 48 species were assessed for cut severity. A subset of 667 trees were for average severity in June and July to understand disease progression. The species and trees presented here, can provide insight for future genetic fire blight resistance studies.