The HPLC-Fluorescence Detection of Coumarins in ‘Hamlin’ Sweet Orange and ‘Marsh’ Grapefruit Leaf Cankers

Authors: Manthey, John; Narciso, Jan

Submitted to: Florida State Horticultural Society Meeting
Publication Type: Proceedings
Publication Acceptance Date: 7/30/2013
Publication Date: N/A
Citation: N/A

Interpretive Summary: The infection by the citrus pathogenic bacterium that causes citrus canker results in plant defense responses. Part of these responses is chemical changes that help combat the invading pathogen. These chemical changes involve the production of compounds called coumarins. The identification of the main coumarins was achieved.

Technical Abstract: Canker is a devastating disease for the citrus fresh fruit market and is caused by the pathogenic bacterium Xanthomonas citri var. citri (Xcc). Infection occurs by bacterial penetration through physical damage of leaves, peel and stems, and also by bacterial entry through the stomates of these photosynthetic tissues. The chemical responses to Xcc infection and subsequent canker formation were characterized by high performance liquid chromatography (HPLC) coupled with mass spectrometry (MS) and fluorescence spectroscopy. Analyses of leaf cankers of ‘Marsh’ grapefruit (Citrus paradisi Macf.) and ‘Hamlin’ sweet orange (C. sinensis, Linn.) showed stimulated production of the structurally related coumarins, umbelliferone, scopoletin, and scoparone. The production of other unidentified coumarins in citrus cankers was also documented. These compounds have been observed under other plant stress conditions in citrus, and it is surmised that these compounds occur as plant defense compounds in response to the resulting tissue damage following Xcc infection.