Metabolomic analyses provide insights into the preharvest rind disorder in Satsuma Owari Mandarin

Abstract

Citrus fruit’s appearance is the primary criterion used to assess its quality for the fresh market, hence the rind’s condition is a crucial quality trait. 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. 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 Mandarins. The study was carried out using ten-year-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), healthy tissue of damaged fruit (DF_HT), and damaged tissue of damaged fruit (DF_DT). Damaged fruit (DF_HT and DF_DT) showed lower cellulose concentrations than healthy fruit tissues (HF_HT), however, had similar contents of pectin and hemicellulose. The antioxidant activities showed no significant difference in all paired comparisons between samples as expressed in the malondialdehyde (MDA) content. However, DF_DT had a higher H2O2 content compared to HF_HT, but 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 revealed that a total of 76 metabolites were identified in Satsuma rind tissues, and the relative concentrations of 43 metabolites were significantly different across studied samples. The hormonal analysis showed the involvement of jasmonate O-methyltransferase, jasmonic acid-amido synthetase JAR1-like, and JA-isoleucine may key role in causing the rind disorder in mandarins. In addition, the damaged fruit tissues have a higher level of jasmonic acid (JA), 12-oxo-phytodienoic acid, and JA-isoleucine than undamaged tissue.

Preharvest Mandarin Rind Disorder: Insights into Varietal Differences and Preharvest Treatments Effects on Postharvest Quality

“…This issue primarily impacts early varieties, such as Owari Satsuma, and carries economic consequences. The first documented occurrence of this damage was by Adaskaveg et al [ 30 ] and Pervaiz et al [ 5 ], and our data align with their findings. Our research indicates that this damage begins as clear areas on the rind that progressively turn brown over time, consistent with the observations made by Adaskaveg et al [ 30 ].…”

“…Notably, citrus fruits within the canopy exhibit distinct characteristics, including a thicker wax layer, as reported by Ritenour and Dou [ 31 ] and Romero and Lafuente [ 32 ]. In addition, a comprehensive metabolome analysis has revealed a wide range of differences between fruits inside and outside the canopy [ 5 , 33 ]. The occurrence of damage exclusively in Owari Satsuma may be attributed to genetic variations between Satsuma and other varieties, as well as differences in maturation times.…”

“…Up to 60% of the overall output of fruit might be impacted by physiological disorders [ 2 ]. Physiological rind disorders include rind breakdown, chilling injury, non-chilling rind/peel pitting and rind staining, peteca spots, puffiness, creasing, stylar end breakdown, oleocellosis, and stem-end rind breakdown (SERB) [ 3 , 4 , 5 ]. Externally, non-chilling physiological rind disorder symptoms may seem similar to postharvest chilling injury symptoms.…”

“…Externally, non-chilling physiological rind disorder symptoms may seem similar to postharvest chilling injury symptoms. The majority of non-chilling rind disorders affect both the albedo and Plants 2024, 13, 1040 2 of 16 the flavedo tissues, and the fruit may be susceptible to the disorder while still connected to the tree [4,5].…”