Detection of phenylpropenoids in citrus leaves produced in response to Xanthomonas citri subsp citri

Authors: Ference, Christopher; Manthey, John; NARCISO, JAN - Retired ARS Employee; JONES, JEFFREY - University Of Florida; BALDWIN, ELIZABETH - Retired ARS Employee

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/7/2019
Publication Date: 1/5/2020
Citation: Ference, C.M., Manthey, J.A., Narciso, J.A., Jones, J.B., Baldwin, E.A. 2020. Detection of phenylpropenoids in citrus leaves produced in response to Xanthomonas citri subsp citri. Phytopathology. 110:287-296. https://doi.org/10.1094/phyto-06-19-0219-R.
DOI: https://doi.org/10.1094/phyto-06-19-0219-R

Interpretive Summary: Citrus canker (CC), caused by the bacterial pathogen Xanthomonas citri subsp. citri, impacts citrus production in many areas of the world by reducing yields, degrading tree health, and severely blemishing the outer peels of fresh fruit. This investigation compares the responses to infection with Xanthomonas bacteria in 5 varieites of citrus. The investigated responses were the production of potential plant defense compounds. In response to the bacterial infection, all citrus varieties showed increased levels of these defensive compounds, whereas the similarly treated nonhost orange jessamine (Murraya paniculata) did not. The actual involvement of these defense compounds is still a point of study.

Technical Abstract: Citrus canker (CC), caused by the bacterial pathogen Xanthomonas citri subsp. citri, impacts citrus production in many areas of the world by reducing yields, degrading tree health, and severely blemishing the outer peels of fresh fruit. The relative susceptibility to CC among different species of Citrus varies from the highly susceptible lime (Citrus × aurantifolia), sweet orange (C. × sinensis), and grapefruit (C. × paradisi) to the much less susceptible calamondin (C. × microcarpa) and kumquat (C. japonica). This investigation compares the responses to infection with X. citri subsp. citri of these five genotypes with respect to phenylpropanoid compound profiles and relative increases or decreases of specific compounds postinoculation. In response to X. citri subsp. citri infection, all hosts possessed increased concentrations of phenylpropanoids in leaf tissue, whereas the similarly treated nonhost orange jessamine (Murraya paniculata) did not. Several of the tested genotypes exhibited notably increased production of fluorescent phenylpropanoids, including umbelliferone, herniarin, auraptene, scoparone, and others. The profiles of these compounds and their levels of production varied among the tested species yet all investigated Citrus genotypes exhibited increased concentrations of phenylpropanoids regardless of their degree of susceptibility to X. citri subsp. citri. Kumquat and calamondin, the tested genotypes least susceptible to X. citri subsp. citri, also exhibited the highest levels of the dihydrochalcone 3',5'-di-C-glucosyl phloretin, the aglycone portion of which, phloretin, is a known antibiotic, although levels of this compound were not affected by inoculation with X. citri.