Russeting in Apple Seems Unrelated to the Mechanical Properties of the Cuticle at Maturity

Khanal, Bishnu P.; Shrestha, Rejina; Hückstädt, Leonie; Knoche, Moritz

doi:10.21273/hortsci.48.9.1135

Cited by 17 publications

(17 citation statements)

References 19 publications

(34 reference statements)

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“…The findings presented in this article and the sequence of events outlined are consistent with the previously reported absence of significant relationships between the russeting susceptibilities of particular apple cultivars and the mechanical characteristics of their CM at maturity (Khanal et al, 2013a). Relationships between russet susceptibility and the rate of wax deposition and filling of cuticular cracks or russet susceptibility and the mechanical properties of epidermal and hypodermal cell layers would be more likely.…”

Section: Discussionsupporting

confidence: 90%

“…An uniaxial tensile force was applied at a constant strain rate of 3 mmÁmin -1 until failure of the ES or CM. Applied force and crosshead travel (in millimeters) were recorded and maximum force F max (in Newtons) and travel at F max (in millimeters) were extracted from the data and the strain at F max e max ð Þ was calculated (Khanal et al, 2013a). Stiffness (S in Newtons) was calculated as the maximum slope of the force (Newtons) vs. fractional strain (in percent per 100) relationship.…”

Section: Methodsmentioning

confidence: 99%

“…Appearance is an important quality attribute in fresh fruit with cosmetic blemishes significantly reducing their value, especially in the premium export market. In apple, commercially relevant examples include the skin disorders russeting (Khanal et al, 2013a) and skin spots (Grimm et al, 2012a). The etiology of both of these disorders involves mechanical failure of the fruit skin with cuticular microcracking being the first detectable symptom Shear, 1972a, 1972b;Grimm et al, 2012a).…”

mentioning

confidence: 99%

“…In apple, however, the pattern is different. Throughout fruit development, cuticle material is deposited as the area of the skin surface expands with no apparent buildup of reversible elastic strain (Khanal et al, 2013a(Khanal et al, , 2013b. Nevertheless, micrographs from scanning electron microscopy (SEM) of apple fruit surfaces often reveal a network of fine cuticular cracks, even in the absence of any russeting (Curry, 2012;Faust and Shear, 1972b;Maguire et al, 1999;Roy et al, 1999).…”

mentioning

confidence: 99%

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Mechanical Properties of Apple Skin Are Determined by Epidermis and Hypodermis

Khanal

Knoche

2014

J. Amer. Soc. Hort. Sci.

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Mechanical failure of the fruit skin is an early event in the etiology of the disorders russeting and skin spots in a number of apple cultivars including ‘Elstar’ (Malus ×domestica Borkh.). The objective was to quantify the mechanical properties of excised epidermal segments (ES) of fruit skin and of enzymatically isolated cuticular membranes (CM) using uniaxial tensile tests. ES thickness ranged from 0.25 to 1.8 mm because thin ES samples of more uniform thickness are difficult to prepare. Sample values for stiffness (S), maximum force () and strain at () were recorded. Measured values were adjusted by regression to refer to a hypothetical standard ES of 0.5 mm thickness. Generally, S and values were positively related to ES thickness during the preharvest period from 51 to 141 days after full bloom (DAFB) and during the postharvest period from 141 to 259 DAFB in cold storage (1.7 °C, 92% relative humidity). The recorded were independent of ES thickness. The S of a standardized ES decreased slightly from 51 to 90 DAFB, then increased up to 161 DAFB, and then declined. There were essentially no differences in S recorded for isolated CM and ES. The and were highest in young fruit at 51 DAFB but decreased steadily toward harvest and continued to decrease in cold storage after harvest but at a lower rate. The and were markedly lower for CM samples than for ES ones. Monitoring the increased incidence of CM microcracking during a tensile test performed on an ES revealed that CM failure preceded ES failure. The decrease in the for ES during fruit development was accounted for in part by a decrease in the mass of cell wall per unit surface area. Our results show that the epidermal and hypodermal cell layers represent the structural backbone of an apple skin during pre- and postharvest development. Furthermore, CM microcracking has limited relevance to the overall mechanical properties of the skin.

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Section: Discussionsupporting

confidence: 90%

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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Mechanical Properties of Apple Skin Are Determined by Epidermis and Hypodermis

Khanal

Knoche

2014

J. Amer. Soc. Hort. Sci.

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“…Apple cultivars differ in their susceptibility to russeting [ 13 ]. Based on its susceptibility to russeting, a cultivar can be assigned to one of three arbitrary susceptibility categories: low, intermediate, or high.…”

Section: Introductionmentioning

confidence: 99%

Russet Susceptibility in Apple Is Associated with Skin Cells that Are Larger, More Variable in Size, and of Reduced Fracture Strain

Khanal

et al. 2020

Plants

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Russeting is an economically important surface disorder in apple (Malus × domestica Borkh). Indirect evidence suggests an irregular skin structure may be the cause of the phenomenon. The objective of this study was to characterize epidermal and hypodermal cell morphology and the mechanical properties of the skins of apple cultivars of differing russet susceptibility. Dimensions of epidermal and hypodermal cells were determined using microscopy. Stiffness (S), maximum force (Fmax), and maximum strain (εmax) at failure were quantified using uniaxial tensile tests of skin strips. Particularly during early fruit development, epidermal cells (EC) and hypodermal cells (HC) in russet non-susceptible cultivars occurred in greater numbers per unit area than in russet-susceptible ones. The EC and HC were lower in height, shorter in length, and of reduced tangential surface area. There were little differences in S or Fmax between non-susceptible and susceptible cultivars. However, the εmax were higher for the skins of non-susceptible cultivars, than for those of susceptible ones. This difference was larger for the young than for the later growth stages. It is concluded that russet-susceptible cultivars generally have larger cells and a wider distribution of cell sizes for both EC and HC. These result in decreased εmax for the skin during early fruit development when russet susceptibility is high. This increases the chances of skin failures which is known to trigger russeting.

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