Peel degreening is an important aspect of fruit ripening in many citrus fruit, and previous studies have shown that it can be advanced by ethylene treatment or by low-temperature storage. However, the important regulators and pathways involved in natural peel degreening remain largely unknown. To determine how natural peel degreening is regulated in lemon fruit (Citrus limon), we studied transcriptome and physiochemical changes in the flavedo in response to ethylene treatment and low temperatures. Treatment with ethylene induced rapid peel degreening, which was strongly inhibited by the ethylene antagonist, 1-methylcyclopropene (1-MCP). Compared with 25 ºC, moderately low storage temperatures of 5–20 °C also triggered peel degreening. Surprisingly, repeated 1-MCP treatments failed to inhibit the peel degreening induced by low temperature. Transcriptome analysis revealed that low temperature and ethylene independently regulated genes associated with chlorophyll degradation, carotenoid metabolism, photosystem proteins, phytohormone biosynthesis and signalling, and transcription factors. Peel degreening of fruit on trees occurred in association with drops in ambient temperature, and it coincided with the differential expression of low temperature-regulated genes. In contrast, genes that were uniquely regulated by ethylene showed no significant expression changes during on-tree peel degreening. Based on these findings, we hypothesize that low temperature plays a prominent role in regulating natural peel degreening independently of ethylene in citrus fruit.

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Maintenance of green peel is desirable during storage and marketing of sudachi (Citrus sudachi Hort. ex Shirai) fruit. This study investigated the potential of edible coatings and 1-methylcyclopropene (1-MCP) treatment in extending the postharvest life during storage at 10, 15, and 20°C. Edible coatings were applied on freshly harvested green sudachi fruit either as a layer by layer (LBL), which involved alternate deposition of chitosan and alginate, or as an ion complex (IC) coating, which involved one-time deposition of a chitosan and alginate mixture. Storage at 10°C maintained the green peel color for up to 15 d with no significant differences among the treatments. At 15 and 20°C, the edible coatings significantly lowered ethylene production and respiration rates, and noticeably maintained green peel color for up to 19 d when applied as tri-layer IC, and 15 d when applied as tri-layer LBL. In addition, tri-layer IC coatings during storage at 15°C appeared to be more effective as they further extended the green peel stage to 21 d compared with 7 and 11 d for mono-and bilayer coatings, respectively. By contrast, 1-MCP treatment failed to inhibit peel yellowing, but instead stimulated fruit respiration and ethylene production. From these results, it is evident that edible coatings may provide a promising postharvest method to extend the postharvest life and preserve the quality of sudachi fruit.

AbstractPeel degreening is an important aspect of fruit ripening in many citrus fruit, and earlier studies have shown that it can be advanced either by ethylene treatment or during low temperature storage. However, the important regulators and pathways involved in natural peel degreening remain largely unknown. To understand how natural peel degreening is regulated in lemon (Citrus limon L.) fruit, flavedo transcriptome and physiochemical changes in response to either ethylene treatment or low temperature were studied. Ethylene treatment induced rapid peel degreening which was strongly inhibited by the ethylene antagonist, 1-methylcyclopropene (1-MCP). Compared with 25°C, moderately low temperatures (5°C, 10°C, 15°C and 20°C) also triggered peel degreening. Surprisingly, repeated 1-MCP treatments failed to inhibit the peel degreening induced by low temperature. Transcriptome analysis revealed that low temperature and ethylene independently regulated genes associated with chlorophyll degradation, carotenoid metabolism, photosystem proteins, phytohormone biosynthesis and signalling, and transcription factors. On-tree peel degreening occurred along with environmental temperature drops, and it coincided with the differential expression of low temperature-regulated genes. In contrast, genes that were uniquely regulated by ethylene showed no significant expression changes during on-tree peel degreening. Based on these findings, we hypothesize that low temperature plays a prominent role in regulating natural peel degreening independently of ethylene in citrus fruit.HighlightCitrus peel degreening is promoted by low temperature via modulation of multiple genes associated with chlorophyll degradation, carotenoid biosynthesis, photosystem disassembly, phytohormones and transcription factors without involving ethylene signalling.

For marine transport bound for North America of three astringent-type persimmons, 'Tonewase', 'Hirateneashi', and 'Nakataniwase', optimum temperature and efficacy of 1-MCP treatment were studied for fruit transported in carton boxes coated with a water-impervious material. In addition, the effect of MA packaging was investigated in 'Tonewase' fruit. On the whole, a lower temperature ranging from 25 to 0°C resulted in longer control of fruit softening in 'Tonewase' fruit; however, fruit stored at 5 and 10°C showed symptoms of chilling injury. The benefit of 1-MCP treatment at harvest persisted for up to two weeks at 25 and 20°C, three weeks at 15 and 10°C, four weeks at 5°C, and 1 week at 25°C following one-month storage at 0°C. MA packaging using polyethylene film had significant inhibitory effects on fruit softening at low temperature, while its additive effects with 1-MCP treatment were limited. In 'Nakataniwase', fruit softening progressed immediately after transfer to 25°C following one-month storage at 0°C, even in fruit treated with 1-MCP. In 'Hiratanenashi', fruit stored at 0°C for one month did not soften for up to 10 days after transfer to 25°C, regardless of 1-MCP treatment. These results suggest that the optimum temperature for marine transport bound for North America, possibly taking around one month, is 0°C. In addition, 1-MCP treatment at harvest is not sufficient to retain commercial fruit quality during shelf life after marine transport in 'Nakataniwase' fruit. In 'Tonewase', the combination of marine transport at 0°C and 1-MCP treatment at harvest or MA packaging can effectively inhibit softening during shelf life following marine transport. In 'Hiratanenashi' fruit held at 0°C, 1-MCP treatment is not necessary to maintain fruit quality for up to 10 days during shelf life following marine transport.