Abstract
Huanglongbing (HLB) presumably caused by Candidatus Liberibacter asiaticus (CLas) threatens the commercial U.S. citrus crop of an annual value of $3 billion. The earliest shift in metabolite profiles of leaves from greenhouse-grown sweet orange trees infected with Clas, and of healthy leaves, was characterized by HPLC-MS concurrently with PCR testing for the presence of Clas bacteria and observation of disease symptoms. Twenty, 8-month-old ‘Valencia’ and ‘Hamlin’ trees were grafted with budwood from PCR-positive HLB source trees. Five graft-inoculated trees of each variety and three control trees were sampled biweekly and analyzed by HPLC-MS and PCR. Thirteen weeks after inoculation, Clas was detected in newly growing flushes in 33% and 55% of the inoculated ‘Hamlin’ and ‘Valencia’ trees, respectively. Inoculated trees remained asymptomatic in the first 20 weeks, but developed symptoms 30 weeks after grafting. No significant differences in the leaf metabolite profiles were detected in Clas-infected trees 23 weeks after inoculation. However, 27 weeks after inoculation, differences in metabolite profiles between control leaves and those of Clas-infected trees were evident. Affected compounds were identified with authentic standards or structurally classified by their UV and mass spectra. Included among these compounds are flavonoid glycosides, polymethoxylated flavones, and hydroxycinnamates. Four structurally related hydroxycinnamate compounds increased more than 10-fold in leaves from ‘Hamlin’ and ‘Valencia’ sweet orange trees in response to Clas infection. Possible roles of these hydroxycinnamates as plant defense compounds against the Clas infection are discussed.
Highlights
Citrus greening disease, known as huanglongbing (HLB), is the most destructive citrus disease worldwide [1]
It is believed to be caused by the bacterium Candidatus Liberibacter asiaticus (Clas), which is transmitted by the Asian citrus psyllid (Diaphorina citri, ACP) [1]
The objective of our study was to evaluate biochemical changes that occur in the leaves of Clas-infected sweet orange trees over time
Summary
Known as huanglongbing (HLB), is the most destructive citrus disease worldwide [1]. It is believed to be caused by the bacterium Candidatus Liberibacter asiaticus (Clas), which is transmitted by the Asian citrus psyllid (Diaphorina citri, ACP) [1]. HLB was discovered in the largest citrus growing regions in the USA and Brazil [2]. HLB symptoms are displayed on different parts of the plant; the leaves are characterized by a yellow blotchy mottle, or asymmetrical chlorosis, and the fruits are under-developed, lopsided, and green colored with aborted or stained seeds [3]. As the disease severity increases, both yield and fruit quality decrease. Yield reduction due to fruit drop can reach 30 to 100% [1]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
