ARS | Publication request: Differences in secondary metabolites in leaves from orange trees (Citrus sinensis L.) affected with greening disease (Huanglongbing) (HLB)

Submitted to: Proceedings of Florida State Horticultural Society
Publication Type: Proceedings/Symposium
Publication Acceptance Date: November 19, 2008
Publication Date: April 1, 2009
Citation: Manthey, J.A. 2008. Differences in secondary metabolites in leaves from orange trees (Citrus sinensis L.) affected with greening disease (Huanglongbing) (HLB). Proceedings of Florida State Horticultural Society. 121:285-288.

Interpretive Summary: An emerging damaging disease termed Huanglongbing (HLB) in citrus has attracted a great deal of attention by the US citrus industry. There is a need to understand the effects of this disease on the chemical composition of leaves and fruit of affected trees. This study deals with an analysis of the changes in the chemical composition of HLB-affected leaves. Many of the compounds in orange leaves show strong fluctuations when influenced by this disease. These findings will help the US citrus industry understand to impacts of this disease on citrus trees, and ultimately on juice quality and taste.

Technical Abstract: Preliminary analyses by HPLC-MS of methanolic extracts of two sets of orange leaves that are symptomatic of the Greening Disease (HLB) have shown several consistent differences. The main flavonoids in symptomatic and nonsymptomatic leaves were monitored in the HPLC chromatograms at 330 nm, and significant differences were detected in certain hydroxycinnamates and flavone glycosides between the symptomatic and un-diseased leaves. Other differences were detected in the Total-Ion-Currents (TICs) of the mass spectral analyses of the leaf extracts. One main difference was the elevated concentration of a compound with a m/z of 187 amu, which was also visualized as an Ehlrich reagent positive band in normal phase TLC of symptomatic leaf extracts. Ehlrich reagent is useful for the detection of limonoids, as well as secondary amines, including alkaloids. Work is in progress to identify this compound.