Effect of fruit bagging on chlorophyll degradation and related gene expression in nectarine peel

Abstract:【Objective】The peach (Prunus persica L.) is a stone fruit crop with high economic value, favored by consumers worldwide for its rich flavor and nutritional value, and is one of the main fruits consumed in many countries. Currently, fruit quality has become a key factor influencing consumers’ choice. Among fruit quality attributes, skin color is one of the most intuitive factors that consumers consider when selecting fruits. Chlorophyll content is a crucial factor affecting the base color of the fruit skin and the overall appearance of the fruit, as it is closely related to fruit ripening. However, there has been no report about the impact of bagging on the degradation of chlorophyll genes in peaches. In this study, two nectarine varieties with similar ripening periods were used as materials to preliminarily explore the effects of bagging on the degradation pattern of chlorophyll in nectarine skin and the expression of genes related to chlorophyll degradation, with the aim of providing a basis for determining the ripening period of nectarine fruits and the differences in base color.【Methods】Using two nectarine va-rieties Zhongyou No. 18 and Zhongyou No. 19 as subjects of the study, the color changes of fruit peels before ripening were quantified using a colorimeter, and the chlorophyll contents were measured using a UV spectrophotometer. There has been no report on the expression of chlorophyll degradation genes in bagged peach fruits to date. To fill this gap, the expression of genes related to chlorophyll degradation was detected using real-time quantitative polymerase chain reaction (qRT-PCR), and the coding sequences (CDS) of the relevant genes were sourced from genomic databases. By establishing the correlation between chlorophyll degradation and gene expression through statistical analysis, the impact of bagging on the chlorophyll degradation in nectarine fruit skin was determined.【Results】The L* values (indicating the lightness or darkness of color) of the fruit skin for the bagged Zhongyou No. 18 and Zhongyou No. 19 nectarine varieties showed a significant increase compared to the control, which suggested that bagging could enhance the brightness of the fruit and improve its color. For both Zhongyou No. 18 and Zhongyou No. 19, the a* values (representing the red-green color axis) of the fruit skin rose rapidly from 44 to 12 days before full maturity (DBM), with the bagged fruits exhibiting a more rapid increase in a* values than the control. Bagging accelerated the increase in a* values during this period, leading to lighter coloring and a cleaner base color of the fruit skin compared to the control. Bagging resulted in a decrease in the b* values (indicating the yellow-blue color axis) for white-fleshed peaches, whereas in yellow- fleshed peaches, bagging led to an increase in b* values. From 44 to 12 DBM, the chlorophyll content in bagged fruits significantly decreased compared to the control. Therefore, bagging treatment accelerated the degradation of chlorophyll in the fruit skin. After bagging, the chlorophyll content in the varieties reached the harvest level approximately one week earlier than the control. The fluorescence quantitative results indicated that the expression levels of PpCLH1 in bagged fruits at 23 and 12 DBM were higher than those in the control. The expression of PpPAO increased during the ripening process of Zhongyou No. 19 fruits. The PpSGR gene was significantly and more highly expressed in fully mature fruits of both Zhongyou No. 18 and Zhongyou No. 19 compared to the control, and its expression was advanced and markedly higher after bagging treatment at 23 DBM.【Conclusion】This study investigated the impact of bagging on the expression of chlorophyll degradation genes and analyzed its relationship with color difference and chlorophyll content. It was found that bagging led to the premature high expression of chlorophyll degradation genes PpCLH1, PpPAO and PpSGR, indicating that PpCLH1, PpPAO and PpSGR were key genes in the degradation of chlorophyll in the skin of nectarine fruits before ripening. This provides a new perspective for further elucidating the degradation of chlorophyll in the skin during the development of peach fruits and also offers a reference for exploring the molecular mechanisms of chlorophyll degradation during peach fruit development.