Preharvest Spray Hexanal Formulation Enhances Postharvest Quality in 'Honeycrisp' Apples by Regulating Phospholipase D and Calcium Sensor Proteins Genes.

Karthika Sriskantharajah,Walid El Kayal,Murali Mohan Ayyanath,Gopinadhan Paliyath,Jayasankar Subramanian,Praveen K Saxena,Alan J Sullivan

doi:10.3390/plants10112332

Abstract

‘Honeycrisp’ (Malus domestica Borkh.), a premium applecultivar, is highly susceptible to bitter pit and decline in quality during long-term storage. In order to enhance the quality, an aqueous composition containing hexanal was applied as a preharvest spray. The effects of hexanal were assessed on the treated fruit and compared with HarvistaTM (a sprayable 1-Methylcyclopropene based commercial formulation) applied and control fruit under both cold (2.5 °C; four months) and cold after room temperature storage (20 °C; 14 days) conditions. Color, firmness, and total soluble solids (TSS) did not show a significant change in response to any treatment at harvest, while abscisic acid (ABA) significantly reduced and tryptophan increased in response to hexanal, compared to HarvistaTM and control. The treatment effects on quality traits were observed during storage. Both hexanal and HarvistaTM sprayed apples had higher TSS under both cold and room temperature storage. In addition, both sprays enhanced firmness at room temperature storage. However, the effects of sprays on other quality traits showed a different pattern. Apples sprayed with hexanal had lower phospholipase D enzyme (PLD) activity, lower incidence of bitter pit, and decreased expression of MdPLDα1 compared to HarvistaTM and control. On the other hand, HarvistaTM treated fruit produced lower ethylene. Both sprays decreased the expression of MdPLDα4, MdCaM2, MdCaM4 and MdCML18 genes. Generally, PLD alpha has a direct role in promoting fruit senescence, whereas the calcium senor proteins (CaM/CMLs) may involve in fruit ripening process via calcium and ethylene interactions. Therefore, improved postharvest qualities, including the lower incidence of bitter pit in hexanal treated ‘Honeycrisp’, may be associated with lower membrane damage due to lower PLD enzyme activity and decreased expression of MdPLDα1 and MdPLDα4 genes throughout the storage period.

Highlights

We previously reported that preharvest spray hexanal formulation delayed fruit abscission in ‘Honeycrisp’ most likely by minimizing abscisic acid (ABA) through an ethylene-dependent mechanism [41]
Significant changes in phytohormones levels were observed among the treatments (Table 1)
phospholipase D (PLD) activity in the HarvistaTM treated fruit fluctuated throughout the storage. These results showed that hexanal could inhibit the PLD activity by 19% compared to control at 120 days postharvest, while HarvistaTM can reduce only about 5% respective to control

Summary

Introduction

‘Honeycrisp’, a premium apple variety (Malus domestica Borkh), is mainly produced for fresh market. Since the year 2000, the production area and volume have risen tremendously due to increasing consumer demands [1,2]. Even though ‘Honeycrisp’ can make a profitable venture, the variety is highly susceptible to several serious physiological problems in common cold storage. Storing apples in long-term common cold storage frequently results in declining quality traits such as soluble solids, juiciness, and flavor [3,4]. Phytohormonesand metabolites a* b* Lightness (L) Chroma (C) Hue Angle (H) B*.

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