In a study conducted by scientists from the São Carlos Chemistry Institute (IQSC), Embrapa Instrumentation, Federal University of Technology – Paraná (UTFPR) and Institute of Chemistry of the Federal University of Goiás (UFG) the variation of the fatty acids composition of plants affected by citrus sudden death (CSD) was analyzed. The article resulting from the research was published in January in the Journal of the Brazilian Chemical Society and the analysis of fatty acids represents an alternative method to support the CSD diagnosis.
The study, financed by CAPES (Coordination of Improvement of Higher Education Personnel), FAPESP (The São Paulo Research Foundation), CNPq (National Council for Scientific and Technological Development) and Finep (Financier of Studies and Projects), started by collecting the barks of Rangpur lime (Citrus limonia Osbeck) rootstocks and Valencia orange (Citrus sinensis Osbeck) scions of trees with CSD symptoms – mild or severe – and without.
From the triacylglycerides (oils) (TAG) extracted from these samples were obtained the fatty acid methyl esters (FAME). The FAMEs were identified by gas chromatography by comparing the elution time of the samples with FAME standards, while their relative concentrations were obtained from the signal of the flame-ionization detection (GC-FID).
The fatty acid methyl esters found at lower concentrations in the TAG were capric, lauric, myristic, and stearic acids, while at higher concentrations were palmitic, oleic, linoleic, and linolenic. Capric, lauric, and myristic acids presented an increase in concentration in the rootstock samples in line with CSD symptoms, while stearic and linoleic acids presented an increase in both the rootstock and the scion. Linolenic and oleic acids had their concentrations decreased in line with CSD symptoms in both the rootstock and the scion.
The study proceeded with the chemometric treatments, utilizing the SIMCA and KNN methods, which were used to classify trees between with and without symptoms according to their fatty acids profile. The results obtained were satisfactory, so that this classification can be used as an alternative method to support the citrus sudden death diagnosis.
The cause of this effect of CSD on the tree’s fatty acids profile is unknown. However, the biosynthesis of jasmonic acid (JA) – which, in plants, is involved in regulatory mechanisms in response to biotic and abiotic stresses, such as senescence – from the oxidation of linolenic acid could explain its concentration decrease in line with the symptoms. Moreover, the decrease of oleic acid and increase of linoleic acid may also be related to the JA synthesis, since the biosynthesis of linolenic acid in plants occurs from oleic acid, via linoleic acid.
The citrus sudden death is a disease transmitted by the graft process or by aerial vector, detected only in Brazil, where it caused the eradication of about four million Valencia orange trees. The symptoms of CSD are generalized discoloration and defoliation, thickening of the bark and yellow staining on the bark of the rootstock. The disease destroys the tree’s phloem, affecting its absorption of water and nutrients and, therefore, its productivity and quality of the fruits, causing large losses for the producers.
Post by Natália Wolf.
More information
https://dx.doi.org/10.21577/0103-5053.20220012
Dr. Emanuel Carrilho
Address: Instituto de Química de São Carlos, Universidade de São Paulo, USP, Av. Trabalhador São-carlense, 400, 13566-590 São Carlos, SP, Brasil.
Instituto Nacional de Ciência e Tecnologia de Bioanalítica – INCTBio, 13083-970, Campinas, SP, Brasil.
E-mail: emanuel@iqsc.usp.br