Submitted to: Open Agriculture Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2015
Publication Date: 1/6/2015
Citation: Malik, N.S., Perez, J.L., Kunta, M., Olanya, O.M. 2015. Changes in free polyphenol levels in Satsuma leaves in response to Asian citrus psyllid infestation and water stress. Open Agriculture Journal. DOI: 10.2174/1874331501509010001.
Interpretive Summary: Huanglongbing (HLB), also known as citrus greening disease, has led to devastating losses to the citrus industry in the United States and other countries. The pathogen responsible for this disease is a bacterium Candidatus Liberibacter spp, which is transmitted from plant to plant by the phloem feeding insect Diaphorina citri Kuwayama also known as the Asian citrus psyllids (ACP). To date, the only management option for controlling HLB is through control of the insect vector, principally by insecticidal sprays. To find more effective management methods, we have been investigating biochemical responses of Satsuma leaves to psyllid feeding and water stress. Plants are known to respond biochemically to different stresses as a protective mechanism; polyphenols are well known compounds that plants use to defend against pathogens. The aim of this study was to investigate the possible metabolites involved in these protective responses. The results of this study showed that several secondary metabolites, namely polyphenols, increased in concentration in response to insect and water stress. Some of these compounds, such as rutin, have been reported to act as a biopesticides which may impact insect persistence. Our findings may indicate the possibility of managing ACP infestations via proper water management practices.
Technical Abstract: Huanglongbing (HLB), also referred to as citrus greening disease has caused significant losses to the citrus industry in the United States and elsewhere. In our previous studies, we observed the fluctuation of some primary and secondary metabolites in response to biotic (psyllid feeding) and abiotic (water deficit) stress factors in citrus. In the current report, we evaluated the changes in polyphenolic compounds in Satsuma leaves in response to Asian citrus psyllid feeding stress and the water stress. In general, polyphenolic levels increased in Satsuma leaves in response to insect and water stress. Specifically, polyphenols such as chlorogenic acid, rutin, diosmin, luteolin7-O-glucoside, and narangin levels increased significantly in response to both biotic and abiotic stress. On the other hand, while caffeic acid levels significantly increased in water stressed plants, their levels drastically declined to the level of being undetectable in leaves stressed by psyllid feeding. Differences between the two types of stresses were also observed in the levels of apigenin 7-O-glucoside where it decreased significantly in water stressed leaves but not in leaves stressed by psyllid feeding; i.e. changes in the levels of apigenin 7-O-glucoside and caffeic acid were opposite in response to water or feeding stresses. Hesperidin levels were not affected by the water stress or by psyllid feeding. The findings may help to better understand plant psyllid interactions and may be helpful in developing effective management practices to control the spread of citrus greening disease.