|MGBECHI-EZERI, JOSEPHINE - WASHINGTON STATE UNIVERSITY|
|JOHNSON, KENNETH - OREGON STATE UNIVERSITY|
|NNADOZIE, ORAGUZIE - WASHINGTON STATE UNIVERSITY|
Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/12/2018
Publication Date: 7/9/2018
Citation: Mgbechi-Ezeri, J., Johnson, K.B., Porter, L.D., Nnadozie, O. 2018. Development of a protocol to phenotype sweet cherry (Prunus avium L.) for resistance to bacterial canker. Crop Protection. 112:246-251. https://doi.org/10.1016/j.cropro.2018.06.009.
Interpretive Summary: Bacterial canker caused by Pseudomonas syringae pv. syringae (Pss) is an economically important disease of sweet cherry (Prunus avium L.) in the Pacific Northwest (PNW) of the USA, and other sweet cherry growing regions of the world. The disease induces a variety of symptoms including the oozing of sap from cancers, twig die back and premature abortion of flowers, depending on the plant part infected and aggressiveness of the strain. A combination of methods, including cultural practices, chemical control, and host resistance, is recommended for disease management. Constraints such as lack of resistant cherry lines, the long term nature of the breeding process, and challenges in screening large populations under field conditions to determine resistance, often impede the development of new resistant cultivars. A rapid and efficient method to evaluate sweet cherry germplasm collections to identify resistant lines to bacterial canker is of utmost importance to breeding programs. The present research evaluated the impact of pathogen strains, inoculum concentrations, leaf position on the tree (top, middle, bottom) and whether you can determine resistance to Pss with attached or detached cherry leaves under greenhouse or laboratory conditions that correspond with actual field resistance. Six cherry cultivars were evaluated (Bing, Sweetheart, Regina, Moreau, Emperor Francis and Rainier). It was determined that when screening cherry cultivars for resistance, an inoculum concentration of one hundred million colony forming units of the pathogen, an aggressive strain of the pathogen, and using newly formed detached leaves is the best means of identifying resistance in cherry lines that correponds to field resistance and provides the best separation among cultivars in resistant responses.
Technical Abstract: Suppression of bacterial canker disease of sweet cherry caused by Pseudomonas syringae pv. syringae (Pss), utilizing resistant scion and rootstocks holds promise as a cost effective management strategy. However, a repeatable and rapid method for screening large breeding populations for resistance to Pss poses a challenge. Sweet cherry cultivars Bing, Sweetheart, Regina, Moreau, Emperor Francis and Rainier were used to examine the effects of pathogen strain, inoculum concentration (1 x 102 to 1 x 108 cfu/ml), leaf age (collected from the tip, middle or base of a shoot) and assay method (attached versus detached leaf) on disease development. Disease severity was influenced significantly (P = 0.05) by inoculum concentration and pathogen strain virulence. An inoculum concentration of 1 x 108 cfu/ml provided the best disease response for both leaf assays and is recommended for screening. Also, a significant effect of pathogen strain x cultivar interaction was observed, thus proper selection of Pss strain used for screening is crucial. Disease severity significantly (P = 0.05) decreased with increase in leaf age, and newly expanding leaves in detached assays were more susceptible than new leaves in attached assays. Disease response among cultivars were significantly correlated (r = 0.53, P = 0.0024) in both leaf assays but the detached leaf assay provided a distinctive mean separation between cultivars for disease severity. Detached leaves classified as new, a highly virulent strain, and an inoculum concentration of 1 x 108 cfu/ml can differentiate genotypic variation in disease response among sweet cherry germplasm.