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United States Department of Agriculture

Agricultural Research Service

Research Project: Management and Characterization of Citrus and Date Genetic Resources and Associated Information

Location: National Clonal Germplasm Repository for Citrus

Title: H NMR analyses of Citrus macrophylla subjected to Asian citrus psyllid (Diaphorina citri Kuwayama) feeding

Author
item Chin, Elizabeth
item Godfrey, Kris
item Polek, Marylou
item Slupsky, Carolyn

Submitted to: Arthropod-Plant Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2017
Publication Date: 7/11/2017
Citation: Chin, E., Godfrey, K., Polek, M., Slupsky, C. 2017. H NMR analyses of Citrus macrophylla subjected to Asian citrus psyllid (Diaphorina citri Kuwayama) feeding. Arthropod-Plant Interactions. doi:10.1007/s11829-017-9546-0.

Interpretive Summary: The Asian citrus psyllid (ACP) is a phloem feeding insect that can host and transmit the bacterium, Candidatus Liberibacter asiaticus (CLas), which is the proposed causal agent of the economically important citrus disease, Huanglongbing (HLB) (aka citrus greening disease). This research was conducted to determine a baseline for changes in metabolite concentrations within citrus plants when fed upon by healthy psyllids (not carrying CLas). Different numbers of ACP were allowed to feed on Citrus macrophylla plants maintained within a controlled environment greenhouse. Four psyllid density categories were used; 0 ACP (control), 5 ACP (low), 15-20 ACP (medium), and 25-30 ACP (high). After 7 days of feeding, leaves were collected and analyzed using 1H NMR spectroscopy (Hydrogen or proton-based nuclear magnetic resonance). NMR spectroscopy is the most widely used technology to determine the structure of organic compounds; it is non-destructive and data may be obtained from samples weighing less than a milligram. Results from these analyses suggest ACP density-dependent changes in a plant’s primary metabolism can be measured by H NMR spectroscopy. Metabolite concentrations from leaves of trees with ACP feeding had higher variability than the control trees (no psyllid feeding). Many metabolites were higher in concentration in the low ACP feeding group relative to controls; however, leaves from trees with high ACP feeding had lower concentrations of many metabolites relative to the control, including many amino acids such as phenylalanine, arginine, isoleucine, valine, threonine, and leucine. These amino acids are necessary to mobilize plant defense responses, and therefore these results suggest that higher psyllid feeding densities trigger a greater plant defense response utilizing large numbers of amino acid molecules. Future research will use H NMR spectroscopy to examine metabolic changes in citrus plants when infected with CLas and whether the metabolic profile in response to psyllid feeding differs from the plant response to CLas infection. Host plant metabolic changes may prove useful as a diagnostic tool in the detection of HLB. Host plant responses occur within minutes of infection by a pathogen, whereas symptom expression takes days, months, or years. The ability to identify CLas infected plants soon after infection will slow the disease epidemic.

Technical Abstract: The Asian citrus psyllid (ACP) is a phloem feeding insect that can host and transmit the bacterium Candidatus Liberibacter asiaticus (CLas), which is the putative causative agent of the economically important citrus disease, Huanglongbing (HLB). ACP are widespread in Florida, and are spreading in California; they are the primary mode of CLas transmission in citrus groves. To understand the effects of ACP feeding, different numbers of ACP [0 ACP (control), 5 ACP (low), 15-20 ACP (medium), and 25-30 ACP (high)] were allowed to feed on Citrus macrophylla greenhouse plants. After 7 days of feeding, leaves were collected and analyzed using 1H NMR. Metabolite concentrations from leaves of trees with ACP feeding had higher variability than control trees. Many metabolites were higher in concentration in the low ACP feeding group relative to control; however, leaves from trees with high ACP feeding had lower concentrations of many metabolites relative to control, including many amino acids such as phenylalanine, arginine, isoleucine, valine, threonine, and leucine. These results suggest ACP density-dependent changes in primary metabolism that can by measured by 1H NMR. The implications in plant defense are discussed.

Last Modified: 09/24/2017
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