Inhibiting rachis browning in table grape by postharvest hormonal treatments: Regulation of internal hormone homeostasis’

Description

This study investigated the efficacy of postharvest hormonal treatments in preventing the rachis browning and extending the storage life of 'Fakhri' table grape. The abscission zone of grape clusters was immersed in solutions of melatonin (MT) (250 and 500 µM), cytokinin (CK) (50 and 100 mM), gibberellin (GA) (50 and 100 mM), or auxin (IAA) (50 and 100 mM), for 5 min then stored at 2.5 ± 1 °C and 90–95 % relative humidity for 30 d. The hormonal treatments significantly delayed rachis browning by reducing phenolic oxidation and the activity of key browning enzymes (polyphenol oxidase and peroxidase). Treated rachises maintained higher relative water content and chlorophyll levels, supported by enhanced antioxidant enzyme activity (catalase, superoxide dismutase) that mitigated oxidative stress markers like malondialdehyde and hydrogen peroxide. Hormonal analysis revealed a favorable shift, with increased levels of auxin and gibberellin and a concurrent decrease in abscisic acid in rachis, further confirming delayed senescence. In berries, the hormonal applications prevented firmness loss, reduced weight loss, and better preserved ascorbic acid content. Among all treatments, 500 µM MT, 100 mM CK, and 100 mM IAA were the most effective in maintaining overall visual and nutritional quality. In conclusion, postharvest hormonal treatment, particularly with MT, CK, or IAA, represents a highly promising strategy for suppressing rachis browning and extending the commercial storage life of table grapes by enhancing antioxidant defenses and modulating endogenous hormone balance.

Steps to reproduce

**Materials and Methods (≈2000 characters)** Uniform clusters of table grapes (*Vitis vinifera* cv. Fakhri) were harvested at commercial maturity (TSS ≈ 22 ± 3) from a vineyard in Hamedan, Iran. Healthy clusters with green rachises were transported to the postharvest laboratory and pre-cooled for 10–12 h to remove field heat. The clusters were disinfected in sodium hypochlorite solution (100 μL L⁻¹) for 2 min and rinsed with distilled water. Clusters were divided into nine treatments: distilled water (control), melatonin (250 and 500 μM), cytokinin (6-benzyladenine; 50 and 100 mg L⁻¹), gibberellin (GA₃; 50 and 100 mg L⁻¹), and auxin (IAA; 50 and 100 mg L⁻¹). The rachis ends were recut and immersed in the respective solutions for 5 min. Solutions were prepared with distilled water containing 0.1% Tween-80. Each treatment included three biological replicates with eight clusters per replicate. After treatment, grapes were stored at 2.5 ± 1 °C and 90–95% relative humidity for 30 days, and evaluations were conducted at 0, 10, 20, and 30 days. Rachis browning index (RBI) was assessed using a five-level browning scale. Relative water content (RWC) of the rachis was determined using fresh, turgid, and dry weights. Chlorophyll and carotenoid contents were measured spectrophotometrically after extraction with 80% acetone. Oxidative stress indicators, including malondialdehyde (MDA) and hydrogen peroxide (H₂O₂), were quantified using spectrophotometric assays. Total phenolic compounds (TPC) and total flavonoids (TF) were measured using the Folin–Ciocalteu and aluminum chloride methods, respectively. Activities of antioxidant enzymes (CAT, SOD, POD, and PPO) were determined spectrophotometrically. Endogenous hormones (ABA, IAA, and GA₃) were extracted and quantified using HPLC. Fruit quality parameters including total soluble solids (TSS), titratable acidity (TA), firmness, weight loss, and ascorbic acid content were also measured. Data were analyzed using two-way ANOVA in SAS software, and mean comparisons were performed using Duncan’s multiple range test (*p* < 0.05). Pearson correlation, principal component analysis (PCA), and hierarchical clustering were conducted using R software.

Institutions

• University of Kurdistan

  Kurdistan Province, Sanandaj

Categories

Funders

• This work is based upon research funded by Iran National Science Foundation (INSF) under project No 4046377.

  Grant ID: 4046377

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