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ARS Home » Southeast Area » Fort Pierce, Florida » U.S. Horticultural Research Laboratory » Subtropical Plant Pathology Research » Research » Publications at this Location » Publication #347503

Research Project: Mitigating High Consequence Domestic, Exotic, and Emerging Diseases of Fruits, Vegetables, and Ornamentals

Location: Subtropical Plant Pathology Research

Title: Colonization and movement of Xanthomonas fragariae in strawberry Tissue

Author
item Wang, Hehe - Clemson University
item Mctavish, Christine - US Department Of Agriculture (USDA)
item Turechek, William

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/24/2017
Publication Date: 6/1/2018
Citation: Wang, Hehe, Mctavish, Christine, Turechek, William. 2018. Colonization and movement of Xanthomonas fragariae in strawberry Tissue. Phytopathology. 108:681-690.

Interpretive Summary: Xanthomonas fragariae causes angular leaf spot of strawberry, an important disease in strawberry growing regions worldwide. To better understand how X. fragariae multiplies and moves in strawberry plants, a GFP-labelled strain was constructed and used to monitor the pathogen’s presence in leaf, petiole, and crown tissue with fluorescence microscopy following natural and wound inoculation in three strawberry cultivars. Taqman PCR was used to quantify bacterial densities in these same tissues regardless of the presence of GFP signal. Results showed that X. fragariae colonized leaf and petiole tissue, and was only on occassion found in crown tissue. All bacteria movement appeared to have occured as a passive process. Since leaves are removed as part of the harvesting process, it is likely that petioles harboring bacteria from direct entry through natural openings or wounds serve as a main source of initial inoculum in the field.

Technical Abstract: Xanthomonas fragariae causes angular leaf spot of strawberry, an important disease in strawberry growing regions worldwide. To better understand how X. fragariae multiplies and moves in strawberry plants, a GFP-labelled strain was constructed and used to monitor the pathogen’s presence in leaf, petiole, and crown tissue with fluorescence microscopy following natural and wound inoculation in three strawberry cultivars. Taqman PCR was used to quantify bacterial densities in these same tissues regardless of the presence of GFP signal. Results showed X. fragariae colonized leaf mesophyll, the top 1 cm petiole sections, and was occasionally found colonizing xylem vessels down to the middle sections of petioles. The colonization of vascular bundles and the limited systemic movement appeared to be a passive process, of which the frequency increased with wounding and direct infiltration of bacteria into leaf veins. X. fragariae was able to directly enter petioles and colonize the space under the epidermis. Systemic movement of the bacteria into crown and other un-inoculated tissues was not detected visually by GFP. However, X. fragariae was occasionally detected in these tissues by qPCR, but at quantities very near the qPCR detection limit. Petioles harboring bacteria from direct entry through natural openings or wounds, and from the occasional systemic movement from leaves colonizing the vascular bundles, likely serve as a main source of initial inoculum in the field.