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ARS Home » Pacific West Area » Riverside, California » National Clonal Germplasm Repository for Citrus » Research » Publications at this Location » Publication #350709
Title: ACP and Citrus: Plant Responses to Psyllid Feeding

Author
item Polek, Marylou
item CHIN, ELIZABETH - University Of California, Davis
item GODFREY, KRIS - University Of California, Davis
item LEVESQUE, CYNTHIA - Citrus Research Board
item SLUPSKY, CAROLYN - University Of California, Davis

Submitted to: Citrograph
Publication Type: Trade Journal
Publication Acceptance Date: 10/31/2017
Publication Date: 1/15/2018
Citation: Polek, M., Chin, E., Godfrey, K., Levesque, C., Slupsky, C. 2018. ACP and Citrus: Plant Responses to Psyllid Feeding. Citrograph. Citrograph. Vol 9 No. 1.

Interpretive Summary: In collaboration with scientists at the University of California – Davis, research has been conducted to study the effects of Liberibacter infection on plant metabolism to establish a set of huanglongbing (HLB)-specific metabolic biomarkers. It is hoped that these biomarkers, which move systemically within the plant, could be used to determine whether citrus trees are infected with species of Liberibacter, a bacterial pathogen associated with huanglongbing (HLB, aka citrus greening disease) soon after introduced into the plant. First, what happens within the plant during insect feeding in the absence of the bacteria had to be determined. Asian citrus psyllids (ACP) were raised on healthy sweet orange plants within the University of California – Davis Contained Research Facility. Sweet orange seedlings were infested with zero ACP, low density (10 ACP per plant), medium density (15-20 ACP per plant), and high density (25-30 ACP per plant). After a seven-day feeding period, leaves were collected from each plant and analyzed using proton nuclear magnetic resonance (1H-NMR). There was an inverse linear relationship with psyllid density and levels of the amino acids; arginine, valine, and isoleucine. In contrast, there was an increase in quinic acid as psyllid density increased. These results suggest that ACP feeding lowers the production of secondary metabolites that are involved in plant defense responses. This could potentially decrease the plant’s ability to defend itself against the bacteria being vectored by virulent psyllids. Increased ACP populations feeding on a given tree translates to greater compromise in the production of plant defense metabolites, and therefore leads to increased disease. Whereas, quinic acid is associated with plant stress responses and therefore, its levels would increase within the plant as the number of ACP feeding on the plant increased. Experiments need to be conducted using virulent insects in order to identify specific compounds that could be used as biomarkers to determine whether a plant is infected with HLB-associated bacteria.

Technical Abstract: Progress is reported on the Citrus Research Board funded project: 5300-150 Biomarkers for the detection of Liberibacter infection in citrus through H-NMR-based metabolomics. Proton nuclear magnetic resonance (H-NMR) was used to determine the effects of Asian citrus psyllid (ACP) feeding on leaf metabolite composition in the absence of huanglongbing-associated bacteria. This work served as the foundation for future research to compare the effects of non-infective ACP on the metabolomics profile of citrus leaves versus ACP carrying Liberibacter. Metabolites identified and quantified included sugars and amino acids. Greater numbers of ACP feeding on individual plants induced a greater response than plants with low numbers of insects; with levels of arginine, valine, isoleucine, and phenylalanine decreasing as psyllid densities increased. These amino acids are associated with plant defense responses and may indicate that psyllid feeding lessens the ability of a plant to defend itself against infection by ACP carrying Liberibacter.