Comparative Analyses of Volatile Metabolites Associated With Gene Expression From Non-climacteric and Climacteric Melon.

Melon (Cucumis melo L.) is an important species in the cucurbits family with a large economic importance in the world. Two melon cultivars commercially important in Brazil are the cultivars ‘Yellow’ and ‘Gaúcho’. In addition to the economic importance, these two cultivars display phenotypic differences in aroma, a major trait determining fruit quality. Volatile organic compounds (VOC) impart the different aroma found in these fruit and its biosynthesis is associated with fatty acid and amino acid metabolism. Using SPME-GC–MS and RT-qPCR techniques, volatile production and expression of seven genes (CmLOX9, CmLOX18, CmBCAT1, CmArAT1, CmPDC1, CmADH1 and CmAAT1) were determined during maturation and ripening. The climacteric melon ‘Gaúcho’ had a greater number and higher concentration of volatiles than that in the non-climacteric ‘Yellow’ melon. 2-Methylallyl acetate, 4-amino-1-butanol, 2-methylbutanol and ethyl 2-methylpropanoate were found in high concentrations in ripe climacteric ‘Gaúcho’ melons and were major contributors to its strong fruity aroma, but high concentrations of these volatiles were not found in non-climacteric ‘Yellow’ melons. The lipid pathway played a strong role in determining aroma composition in non-climacteric ‘Yellow’ melons. Most volatiles decreased during maturation and ripening explaining the non-aromatic characteristic of this cultivar. In climacteric ‘Gaúcho’ melons, the amino acid pathway was the main one related to the biosynthesis of esters, which contribute to the aroma of this cultivar. Volatile products of the branched chain amino acid pathway correlated with CmADH1 and CmAAT1 expression demonstrating their role in volatile synthesis of this climacteric melon cultivar. In addition, CmPDC1 contributes to the formation of aldehydes at the beginning of this pathway.