Effect of pre-harvest application of ethephon on colouration and expression of ripening related genes in citrus fruit

Abstract

In citrus, post-harvest treatment with ethylene or ethephon in an airtight container frequently resulted in fruit calyx drying, browning and abscission, with a consequent reduction in commercial value. To avoid these problems, pre-harvest degreening with ethepnon was performed on ‘CARA CARA’ navel orange fruits. An earlier and deeper orange colour development was obtained after treatment, reflecting at higher lightness (L*) and a*/b* ratio. The total carotenoid content in flavedo significantly increased, paralleling with a remarkable decrease in chlorophyll content, while in flesh TSS, TA and Vc were all not affected. A transcriptome analysis revealed that 171 genes in flavedo were involved in ethylene-degreening. These ethylene-responsive genes were involved in photosynthesis, chloroplast biogenesis, sugar metabolism, secondary metabolism, and activation of regulatory processes, including transcription regulation and protein posttranslational modification. In the chlorophyll metabolism, a chlorophyllase gene was strikingly increased, indicating the role of ethylene in promoting chlorophyll degradation. While, the genes related to carotenoid metabolism did not show any significant expression change after ethephon treatments. In conclusion, our data showed that pre-harvest degreening was an effective method to accelerate colour improvement, and meanwhile created a solid foundation for future investigations on the molecular mechanism underlying degreening of orange fruits.

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