Seasonal and post-harvest population dynamics of the Asiatic citrus canker pathogen Xanthomonas axonopodis pv. citri on grapefruit in Florida

Authors: LUO, WEIQI - North Carolina State University; POSNY, DREW - North Carolina State University; KRISS, ALISSA - Syngenta; GRAHAM, JIM - University Of Florida; POOLE, GAVIN - North Carolina State University; Taylor, Earl; MCCOLLUM, GREG - US Department Of Agriculture (USDA); Gottwald, Timothy; Bock, Clive

Submitted to: Crop Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/14/2020
Publication Date: 6/11/2020
Citation: Luo, W., Posny, D., Kriss, A.B., Graham, J.H., Poole, G.H., Taylor, E.L., Mccollum, G., Gottwald, T.R., Bock, C.H. 2020. Seasonal and post-harvest population dynamics of the Asiatic citrus canker pathogen Xanthomonas axonopodis pv. citri on grapefruit in Florida. Crop Protection. 137:105277. https://doi.org/10.1016/j.cropro.2020.105227.
DOI: https://doi.org/10.1016/j.cropro.2020.105227

Interpretive Summary: Asiatic citrus canker (ACC, caused by Xanthomonas citri subsp. citri, [Xcc]) is a serious disease of citrus, reducing yield and impacting marketability of fresh fruit. ACC has phytosanitary implications for fresh fruit trade. Lesions on fruit, leaves, and shoots in an orchard of ACC-susceptible grapefruit was monitored for production of Xcc from June to the following January in 2009 and 2010. Populations of lesions on fruit post-harvest either packingline-treated or not treated were also monitored for production of Xcc on fruit harvested in November 2013 and January 2014. Shoot lesions produced fewer bacteria compared to leaf and fruit lesions. As the season progressed the proportion of active lesions on fruit and shoots declined. Bacterial in surviving lesions high on all organs at all sample times. Analysis revealed weather variables associated with bacterial survival within the lesion. The packingline treatment had no effect in reducing the proportion of active lesions, and had only a small, transient effect reducing quantity of bacteria. Lesion size affected survival – small lesions (<10 mm2) declined in activity rapidly compared to larger lesions, both in the field pre-harvest, and post-harvest in storage. Lesions of ACC on fruit, leaves, and shoots are a constant source of inoculum. Steps to minimize early infection of fruit that often results in large lesions will reduce the risk of inoculum dispersal. Based on these and other previously reported results, lesions on fruit post-harvest can be deemed a limited risk for spread of canker.

Technical Abstract: Asiatic citrus canker (ACC, caused by Xanthomonas citri subsp. citri, [Xcc]) is a serious disease of citrus, reducing yield and impacting marketability of fresh fruit. ACC has phytosanitary implications for fresh fruit trade. Lesions on fruit, leaves, and shoots in an orchard of ACC-susceptible grapefruit was monitored for production of Xcc from June to the following January in 2009 and 2010. Populations of lesions on fruit post-harvest either packingline-treated or not treated were also monitored for production of Xcc on fruit harvested in November 2013 and January 2014. Shoot lesions generally produced fewer bacteria and had a smaller proportion of active lesions compared to leaf and fruit lesions. As the season progressed the proportion of active lesions on fruit and shoots gradually declined. Bacterial flux density (BFD) in surviving lesions was >103 on all organs at all sample times. A window-pane analysis revealed weather variables associated with bacterial survival within the lesion. The packingline treatment had no effect in reducing the proportion of active lesions, and had only a small, transient effect reducing BFD (~1.5 log units). Lesion size affected survival – small lesions (<10 mm2) declined in activity rapidly compared to larger lesions, both in the field pre-harvest, and post-harvest in storage. Lesions of ACC on fruit, leaves, and shoots are a constant source of inoculum. Steps that can be taken to minimize early infection of fruit that often results in large lesions will reduce the risk of inoculum dispersal. Current packingline treatments do not reduce activity of lesions of ACC. Based on these and other previously reported results, lesions on fruit post-harvest can be deemed a limited risk for spread of canker.