QTL analysis reveals the effect of CER1-1 and CER1-3 to reduce fruit water loss by increasing cuticular wax alkanes in citrus fruit

Postharvest water loss causes fruit softening, wilting, and a decline in quality and commodity value. Cuticular wax is a key barrier against non-stomatal water loss and plays a crucial role in fruit quality maintenance. However, there has been limited research on the genetic basis of fruit wax and postharvest water loss. Here, we found that HJ (Citrus reticulata) and ZK (Poncirus trifoliata) fruit had significant differences in postharvest water loss and cuticular wax. HJ fruit had a lower wax content and a faster water loss, and the main aliphatic wax components were alkanes and aldehydes. By contrast, ZK fruit had a higher wax content and a slower water loss, and the main aliphatic wax components were only alkanes. Correlation analysis revealed that fruit water loss seemed to be correlated with cuticular wax alkane in the F₁ pseudo-testcross population of HJ and ZK. Furthermore, through high-density genetic map and bulk segregant analysis, alkanes and fruit water loss were co-localized to QTL3, resulting in the identification of CER1-1 and CER1-3 as the candidate genes. Heterologous overexpression in Arabidopsis revealed that they were involved in alkane synthesis and reduction of leaf water loss. In addition, coating with C28 alkane could reduce postharvest fruit water loss of six citrus varieties. Collectively, we speculated that cuticular wax alkanes might play an important role in limiting fruit water loss. The study provides new insights into the development of coating agents and breeding of citrus varieties with better storage performance.