Abstract
The mango cultivar 'Apple' is commercially important in Kenya but highly susceptible to russeting. Russeting refers to an area of fruit skin where the primary (epidermal) surface has been replaced by a secondary (peridermal) surface. The objective was to establish histologies, gene expressions and chemical compositions of a natural periderm, a wound-induced periderm and of cuticles of an un-russeted skin. Fluorescence microscopy revealed a suberized phellem in natural and wound-induced periderms. Wound-induced periderms had more cell layers and a higher mass than natural periderms. Compared with cuticles, periderms showed decreased expressions of cuticle-related genes (MiSHN1, MiGPAT6, MiCUS1, MiCER1, MiWCB11) and increased expressions of periderm-related genes (MiMYB93, MiNAC058, MiCYP86A1, MiCYP86B1, MiGPAT5, MiABCG20). Natural periderms and wound-induced periderms contained cutin and suberin monomers (C16-C28), including carboxylic, dicarboxylic, and ω-hydroxy acids and primary alcohols. Cuticles of the primary skin contained cutin monomers of similar chemistry but shorter chain lengths (C16-C22). The wax composition in natural and wound-induced periderms was similar to that in cuticles. Lignin monomers in natural and wound-induced periderms contained p-hydroxyphenyl, guaiacyl and syringyl units, but only traces of these occurred in cuticles. In 'Apple' mango, the histologies, gene expressions and compositions of natural and wound-induced periderms are largely the same.