Metabolomic analyses provide insights into the pre-harvest rind disorder in Satsuma Owari mandarin

Authors: PERVAIZ, TARIQ - UNIVERSITY OF CALIFORNIA; PARK, SUEJIN - JEONBUK NATIONAL UNIVERSITY; REZK, ALAAELDIN - UNIVERSITY OF CALIFORNIA; HUR, MANHOI - UNIVERSITY OF CALIFORNIA; Obenland, David - Dave; ARPAIA, MARY LU - UNIVERSITY OF CALIFORNIA; EL-KEREAMY, ASHRAF - UNIVERSITY OF CALIFORNIA

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2023
Publication Date: 9/29/2023
Citation: Pervaiz, T., Park, S., Rezk, A., Hur, M., Obenland, D.M., Arpaia, M., El-Kereamy, A. 2023. Metabolomic analyses provide insights into the pre-harvest rind disorder in Satsuma Owari mandarin. Frontiers in Plant Science. 14. Article 1263354. https://doi.org/10.3389/fpls.2023.1263354.
DOI: https://doi.org/10.3389/fpls.2023.1263354

Interpretive Summary: Pre-harvest browning of the peel in some mandarin varieties that occurs following rain events can sometimes cause significant economic losses to citrus growers. Very little information was available about what causes this to occur was available. Using Satsuma mandarin trees in the San Joaquin Valley of California samples were collected from healthy fruit and from damaged fruit where both healthy and damaged regions were evaluated. Metabolites, antioxidants, and hormones were determined from these samples. Damaged regions of the fruit had a higher concentration of hydrogen peroxide than did other regions and higher levels of enzyme activities potentially involved in browning. Many metabolites were found to differ in amount among the damaged and healthy regions as were levels of plant hormones that may be involved in causing the peel damage to occur. This research provides a means to better understand this damaging disorder and to find ways to prevent its occurrence.

Technical Abstract: Pre-harvest rind disorder is one of the major physiological problems in mandarins. The disorder occurs right before harvest following rain events in some mandarin varieties. The presence of brown lesions on the rind renders the fruits unmarketable. Despite the economic damage caused by this kind of disorder, very limited information is available about the molecular mechanisms underlying the occurrence of this disorder. In the present study, we evaluated the primary metabolites, antioxidants, and hormones associated with the pre-harvest rind disorder in mandarin. The study was carried out using ten-years-old ‘Owari’ Satsuma mandarin trees grafted on ‘Carrizo’ rootstock and grown in a commercial orchard in San Joaquin Valley, California, USA. Samples were collected from healthy tissue of healthy fruit (HF_HT) and healthy tissue of damaged fruit (DF_HT) and damaged tissue of damaged fruit (DF_DT). The antioxidant activities showed no significant difference in all paired comparisons between samples in the malondialdehyde (MDA) content, while DF_DT had a higher H2O2 content compared to HF_HT, and DF_HT had a similar content to that of HF_HT. Furthermore, peroxidase (POD) and polyphenol oxidase (PPO) activities were increased in DF_DT compared to HF_HT (P = 0.0294) and DF_HT (P = 0.0044), respectively. Targeted metabolomics analysis was conducted to identify primary metabolites associated with rind disorder. A total of 76 metabolites were identified in Satsuma rind tissues, and the relative concentrations of 43 metabolites were significantly different across studied samples. In conclusion, the hormonal and metabolomic analysis found that jasmonate O-methyltransferase, jasmonic acid-amido synthetase JAR1-like, and JA-isoleucine, play a critical role under physiological stress.