Objective  Micro-morphology and chemical composition of the wax in pericarps of two varieties of waxy gourd were examined.

  Method   The wax on the pericarps of the differently shaped Xiamaofenpixiaodonggua (XFX) and Xiamaofenpidadonggua (XFD) waxy gourds were examined under a scanning electronic microscope. The epidermal wax composition was analyzed by non-targeted gas chromatography-mass spectrometry (GC-MS) metabolomics.

  Result  Numerous stacked rod-like structures covered the surface of XFX and XFD, but the filamentous material appeared only on XFX. Triterpenoids were the most abundant compounds found in the wax, i.e., 42.09% on XFX and 35.63% on XFD. On the other hand, the esters and alkanes differed significantly between the two varieties, which were 31.16% and 3.53%, respectively, on XFX, and 22.17% and 17.34%, respectively, on XFD. In total, 65 substances in 9 categories were identified that included 11 extremely significantly and 8 significantly differentiated compounds.

  Conclusion   The micro-structures and compositions of the epidermal wax of the two waxy gourd varieties were surprisingly different, and the structural differentiation could be chemically related. Further study to decipher the biosynthesis pathway of the waxy gourd is in order.