Comparative analysis of the crystal morphology, chemical composition and key gene expression between two kumquat fruit cuticular waxes during postharvest cold storage

Waxes have an important protective role in the postharvest storage potential of fruit. However, there are few studies in which the waxes of fruit of kumquat cultivars have been analysed. In this work, the fruit of a kumquat mutant with a relatively thin skin ('Huapi' kumquat, HPK) was found to present lower fruit weight loss and decay during cold storage than the fruit of the control ('Rongan' kumquat, RAK) did. Scanning electron microscopy observations revealed the epicuticular wax crystals on the HPK fruit were more abundant and larger than those on the RAK fruit at harvest. Gas chromatography-mass spectrometry analysis showed the amounts of total wax, triterpenoids and most of the aliphatic wax fractions on the HPK fruit were much higher than those on the RAK fruit throughout the cold storage process. Correlation analysis showed that differences in amounts of fatty acids and aldehydes might be key factors responsible for the differences in the postharvest traits between the two kumquat cultivars. Additionally, the real-time quantitative RT-PCR analysis results indicated that 12 genes involved in wax synthesis, transport and transcription were considered to play important roles in regulating the wax formation of kumquat fruit during cold storage.