|RATTNER, RACHEL - Cooperative Agricultural Support Services|
|HAJERI, SUBHAS - Central California Tristeza Eradication Agency|
|Yokomi, Raymond - Ray|
Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/26/2022
Publication Date: 5/10/2022
Citation: Wallis, C.M., Gorman, Z.J., Rattner, R., Hajeri, S., Yokomi, R.K. 2022. Amino acid, sugar, phenolic, and terpenoid profiles are capable of distinguishing Citrus tristeza virus infection status in grapefruit, lemon, mandarin, and sweet orange leaves. Frontiers in Plant Science. 17(5) Article e0153932. https://doi.org/10.1371/journal.pone.0268255.
Interpretive Summary: The most severe viral disease of citrus is caused by Citrus tristeza virus (CTV). There are many characterized strains of CTV, ranging from those that do not cause symptoms to those that may be fatal to their hosts. Shifts in metabolites that occur in hosts infected by mild or severe strains are not well studied. To resolve this gap in knowledge, grapefruit, lemon, mandarin, and sweet oranges grafted on Carrizo rootstock were infected with mild or severe CTV strains and resulting metabolite profiles were compared with those of healthy trees. Of four major metabolite groups profiled, only overall amino acid levels changed in response to CTV infections, with increased levels observed in citrus trees infected with severe CTV strains versus healthy controls. However, when metabolite profiles were analyzed by canonical discriminant analysis (CDA) individual metabolites belonging to the amino acid, phenolic, or terpenoid classes were observed and could distinguish infection status and cultivar of samples. This could be used by field-deployable equipment to detect severe CTV infections in the field.
Technical Abstract: Citrus tristeza virus (CTV) is the most severe viral disease for citrus production. Many strains of CTV have been characterized and their symptomology widely varies, ranging from mild or asymptomatic infections, to severe symptomology that results in substantial yield loss or host death. The capacity of the different CTV strains to affect the biochemistry of different citrus species has remained largely unstudied, despite that associated metabolomic shifts would be relevant toward symptom development. Thus, amino acid, sugar, phenolic, and terpenoid levels were assessed in leaves of healthy and CTV-infected grapefruit, lemon, mandarin, and two different sweet orange cultivars. Both mild (VT-) and severe (VT+) CTV genotype strains were utilized. When looking at overall totals of these metabolite classes, only amino acid levels were significantly increased by infection of citrus with severe CTV strains, relative to mild CTV strains or healthy plants. No significant trends of CTV infection on overall sugar, total phenolic, or total terpenoid levels were observed. However, canonical discriminant analysis (CDA) utilizing profiles of individual amino acids, terpenoids, or phenolics was able to correctly match leaf samples to specific citrus varieties and identify their infection status with good accuracy. This analysis reliably distinguished citrus infected with mild CTV strains from those infected with severe CTV strains. Collectively, this study reveals biochemical patterns associated with severity of CTV infections that can potentially be utilized to help identify in-field CTV infections of economic relevance.