Tracking the development of the superficial scald disorder and effects of treatments with diphenylamine and 1-MCP using an untargeted metabolomic approach in apple fruit

Superficial scald is still one of the most important postharvest physiological disorders in apples. Commercial control of this disorder has been accomplished by selecting resistant cultivars, treating fruit with DPA and ethoxyquin, using oil-soaked fruit wraps and storing the fruit under low O2. However, the causal reason for scald development is still a mystery. Research has indicated that the scald-promoting factor or inducing compound may be formed or accumulated in apple cuticle then rediffused back into the hypodermis, thereby causing damage. Hydroperoxides, auto-oxidative product from α-farnesene, have been thought to be the toxic compounds, inducing scald; however, it is not explained how the hydroperoxides move from the cuticle to the hypodermis. The identification and dynamic changes of 6-methyl-5-heptene-2-one as a natural volatile in apple fruit during ripening were made, which accumulated in higher quantitaty in cuticular wax than in headspace. The close relationship between the chloroplast breakdown and amount of α-farnesene changes, the induction of scald-like symptom on the surface of apple fruit by 6-methyl-5-heptene-2-one and the sensitivity of fruit to this ketone damage were investigated. Our results suggest that the accumulation of 6-methyl-5-heptene-2-one in the cuticular wax of apple fruit might be the causal reason for scald development in apples.

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Intermittent Warming Effects on Superficial Scald of Apple Fruit

HortScience ◽

10.21273/hortsci.31.4.605b ◽

1996 ◽

Vol 31 (4) ◽

pp. 605b-605

Author(s):

Thair F. Alwan ◽

Christopher B. Watkins

Keyword(s):

Fruit Ripening ◽

Marked Reduction ◽

Apple Fruit ◽

Oxidation Products ◽

Superficial Scald ◽

Cooperative Agreement ◽

Postharvest Treatments ◽

Conjugated Trienes ◽

Hexane Extracts ◽

Intermittent Warming

Fruit of `Cortland', `Delicious' and `Law Rome' were warmed for 24 hours at 20°C either weekly, once every 2 weeks, or once every 3 weeks during storage. The effect of these treatments on fruit ripening and concentrations of alpha-farnesene and conjugated trienes in hexane extracts of the skin were measured during storage. Without warming, scald incidence of the cultivars was 70%, 14%, and 85%, respectively. Intermittent warming treatments resulted in a marked reduction of scald though effectiveness was affected by cultivar. In `Cortland', scald was reduced only by the weekly warming treatment (10%) as was less effective than DPA (1%). In `Delicious', all warming treatments were equally effective. In `Law Rome', weekly warming resulted in better control of scald (3%) than DPA (14%) and less frequent warming was proportionately less effective in controlling the disorder. Concentrations of conjugated trienes at 281 nm did not relate consistently to scald incidence after storage. However, ratios of conjugated trienes of 258 nm or 269 nm with 281 nm strongly support a hypothesis that non-toxic and toxic oxidation products of alpha-farnesene interact and influence the effectiveness of postharvest treatments on scald control (Du and Bramlage, 1993; JASHS 118:807-813). A hypothesis relating the interactions between ripening and scald development will be presented. Supported in part by USDA Specific Cooperative Agreement 58-1931-5-017.

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Expression of Alpha-farnesene Synthase Gene AFS1 in Relation to Levels of Farnesene and Conjugated Trienols in Peel Tissue of Scald-susceptible `Law Rome' and Scald-resistant `Idared' Apple fruit

HortScience ◽

10.21273/hortsci.39.4.782b ◽

2004 ◽

Vol 39 (4) ◽

pp. 782B-782

Author(s):

Steven W. Pechous ◽

Bruce D. Whitaker* ◽

Christopher B. Watkins

Keyword(s):

Sharp Increase ◽

Biosynthetic Pathway ◽

Apple Fruit ◽

Oxidation Products ◽

High Rate ◽

Subsequent Increase ◽

Transcript Levels ◽

Superficial Scald ◽

Apple Peel ◽

Apple Cultivars

Fruit of different apple cultivars vary widely in susceptibility to superficial scald. The genetic and biochemical factors involved in this variation are unknown. Conjugated trienol (CTol) oxidation products of alpha-farnesene have been linked with scald induction, and a high rate of farnesene synthesis in peel tissue of scald-prone apples early in storage is often associated with development of the disorder. Pre-storage treatment of apple fruit with 1-methylcyclopropene (1-MCP) inhibits the early burst of farnesene production and prevents scald, suggesting that ethylene induces transcription of genes involved in farnesene synthesis. We recently cloned a gene from apple peel tissue, AFS1, which encodes alpha-farnesene synthase, the last enzyme in the farnesene biosynthetic pathway. In this study, expression of AFS1 was compared in scaldsusceptible Law Rome (LR) and scald-resistant Idared (IR) apples at harvest and over 20 weeks of storage at 0.5 C. AFS1 transcript levels were closely correlated with accumulation of farnesene and CTols. In fruit of both cultivars, a sharp increase in AFS1 mRNA during the first 4 to 8 weeks of storage preceded a proportional rise in farnesene and a subsequent increase in CTols. However, maximum levels of AFS1 transcript, farnesene, and CTols were, respectively, 2.5-, 4-, and 33-fold greater in LR than in IR apples. Treatment of fruit with 1-MCP at harvest suppressed the increases in AFS1 transcript and farnesene early in storage, but AFS1 expression and farnesene synthesis recovered in LR fruit after 20 weeks. Scald incidence in LR apples after 20 weeks at 0.5 °C plus 1 week at 20 °C averaged 86%, whereas IR fruit had no scald. 1-MCP treatment reduced scald incidence in LR to <1%.

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Volatile Cuticular Components Involved in Superficial Scald

HortScience ◽

10.21273/hortsci.31.4.605a ◽

1996 ◽

Vol 31 (4) ◽

pp. 605a-605

Author(s):

S. Wee ◽

R.M. Beaudry

Keyword(s):

Gas Chromatography ◽

Mass Spectroscopy ◽

Malus Domestica ◽

Apple Fruit ◽

Superficial Scald ◽

Conjugated Trienes ◽

Gas Chromatography Mass Spectroscopy

Autoxidation products alpha-farnesene of have been implicated in superficial scald induction for apple (Malus domestica cv. Cortland Apple) fruit. We suspect the apple cuticle acts as a sink where α-farnesene can accumulate and eventually autoxidize into hydroperoxides, conjugated trienes, 6-methyl-5-hepten-2-one (ketone), and other compounds. These oxidized byproducts may diffuse back into the peel, thereby initiating the scald process. Cortland apples were stored at 0.8°C. Volatile cuticular components were analyzed at 2-week intervals by gas chromatography–mass spectroscopy. Only two scald-related volatiles were found, 6-methyl-5-hepten-2-one and α-farnesene. The identification of these compounds may allow the determination of cuticular involvement in superficial scald, as well as a possible correlation between the volatiles and apple scald development. α-farnesene concentrations initially increased and was followed by a decline, possibly due to its autoxidation.

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Biosynthesis of α-Farnesene in Apple Fruit

HortScience ◽

10.21273/hortsci.32.3.458a ◽

1997 ◽

Vol 32 (3) ◽

pp. 458A-458

Author(s):

H.P.V. Rupasinghe ◽

G. Paliyath ◽

D.P. Murr

Keyword(s):

Enzyme Purification ◽

Apple Fruit ◽

Oxidation Products ◽

Purification And Characterization ◽

Developing Regions ◽

Physiological Disorder ◽

Superficial Scald ◽

Feeding Experiments ◽

Surface Wax

α-Farnesene is an acyclic sesquiterpene hydrocarbon that is a constituent of the surface wax of apples (Malus domestica Borkh.). Although, oxidation products of α-farnesene have been implicated in the development of the physiological disorder superficial scald in apple, the mechanism of α-farnesene biosynthesis has not been studied in detail. We are currently investigating α-farnesene biosynthesis in relation to superficial scald development in apples. Radiolabelled feeding experiments using isolated tissue segments indicated that α-farnesene is derived from trans,trans-farnesyl pyrophosphate (FPP), mainly in the skin rather than cortex. Among the other labeled products detected, farnesol level was over a hundred-fold higher compared to α-farnesene. However, [1-3H] trans,trans-Farnesol was not incorporated into α-farnesene. Feeding radiolabelled FPP to skin tissue segments of scald-developing and normal apples showed differential incorporation of radiolabel into various products. Though the incorporation into α-farnesene was nearly the same, there was higher levels of incorporation into farnesyl esters in normal apples. As well, the levels of radiolabelled in the farnesol fraction was three times higher in scald-developing regions. These results indicate that there are potential difference in the biosynthesis and metabolism of farnesyl components between scald-developing and normal apples. In studies using cell-free extracts, farnesol formation was observed from labeled FPP and was two-fold higher in crude membrane extract compared to crude cytosol. Our results indicate that α-farnesene formation in apple fruit tissue is through FPP and is possibly catalyzed by a single sesquiterpene synthase enzyme. Purification and characterization of this enzyme are in progress.

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Prestorage Heating of Apple Fruit for Enhanced Postharvest Quality: Interaction of Time and Temperature

HortScience ◽

10.21273/hortsci.27.4.326 ◽

1992 ◽

Vol 27 (4) ◽

pp. 326-328 ◽

Cited By ~ 38

Author(s):

Joshua D. Klein ◽

Susan Lurie

Keyword(s):

Lower Incidence ◽

Apple Fruit ◽

Soluble Solids ◽

Postharvest Quality ◽

Superficial Scald ◽

Acid Ratio ◽

Fruit Damage

`Anna' and `Granny Smith' apples (Malus domestics Borkh.) that were kept at 46C for 12 hours or at 42C for 24 hours before storage at 0C were firmer at the end of storage and had a higher soluble solids: acid ratio and a lower incidence of superficial scald than unheated fruit. These heat regimes produced results similar to those obtained by keeping fruit at 38C for 72 or 96 hours before storage. Prestorage regimes of 46C for 24 hours or 42C for 48 hours resulted in fruit damage after storage.

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