Decreased deposition and increased swelling of cell walls contribute to increased cracking susceptibility of developing sweet cherry fruit

Christine Schumann,Lisa Erz,Simon Sitzenstock,Moritz Knoche

doi:10.1007/s00425-020-03494-z

Abstract

Main conclusionDuring fruit development, cell wall deposition rate decreases and cell wall swelling increases. The cell wall swelling pressure is very low relative to the fruit’s highly negative osmotic potential.Rain cracking of sweet cherry fruit is preceded by the swelling of the cell walls. Cell wall swelling decreases both the cell: cell adhesion and the cell wall fracture force. Rain cracking susceptibility increases during fruit development. The objectives were to relate developmental changes in cell wall swelling to compositional changes taking place in the cell wall. During fruit development, total mass of cell wall, of pectins and of hemicelluloses increases, but total mass of cellulose remains constant. The mass of these cell wall fractions increases at a lower rate than the fruit fresh mass—particularly during stage II and early stage III. During stage III, on a whole-fruit basis, the HCl-soluble pectin fraction, followed by the water-soluble pectin fraction, the NaOH-soluble pectin fraction and the oxalate-soluble pectin fraction all increase. At maturity, just the HCl-soluble pectin decreases. Cell wall swelling increases during stages I and II of fruit development, with little change thereafter. This was indexed by light microscopy of skin sections following turgor release, and by determinations of the swelling capacity, water holding capacity and water retention capacity. The increase in cell wall swelling during development was due primarily to increases in NaOH-soluble pectins. The in vitro swelling of cell wall extracts depends on the applied pressure. The swelling pressure of the alcohol-insoluble residue is low throughout development and surprisingly similar across different cell wall fractions. Thus, swelling pressure does not contribute significantly to fruit water potential.

Highlights

Rain cracking is a critical production problem for many fleshy fruitcrops, especially when rainfall occurs during the later stages of fruit maturation
The economic losses associated with rain cracking in this diversity of fruitcrop species range from a minor impairment of fruit quality due to shallow cracks within the cuticle that can trigger russeting (Knoche et al 2011) and increase the incidence of fruit rots (Borve et al 2000) and increase the rate of postharvest water loss (Maguire et al 1999), to deep cracks that propagate down through the cell layers of the skin into the flesh opening the way for massive invasion by insects and rots
The objectives of this study are: (1) to identify any changes in the major cell wall fractions in developing sweet cherry fruit, (2) to quantify cell wall swelling during fruit development and (3) to identify which cell wall fractions account for cell wall swelling during fruit development

Summary

Introduction

Rain cracking is a critical production problem for many fleshy fruitcrops, especially when rainfall occurs during the later stages of fruit maturation. The economic losses associated with rain cracking in this diversity of fruitcrop species range from a minor impairment of fruit quality due to shallow cracks within the cuticle (microcracks) that can trigger russeting (Knoche et al 2011) and increase the incidence of fruit rots (Borve et al 2000) and increase the rate of postharvest water loss (Maguire et al 1999), to deep cracks (macrocracks) that propagate down through the cell layers of the skin into the flesh opening the way for massive invasion by insects and rots. Rain covers are probably the most effective way to mitigate rain damage in sweet cherries but they do not totally eliminate it and they do involve high levels of capital expenditure

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