Differential aroma volatiles in non-climacteric near-isogenic lines of melon as biomarkers of differences of flesh firmness at harvest

Two non-climacteric near-isogenic lines (NILs) of melon (Cucumis melo L.), SC10-2 and SC7-1, containing introgressions of the Korean cultivar \'\'Shongwan Charmi\'\' accession PI161375 (SC) into the Spanish cultivar \'\'Piel de Sapo\'\' (PS) were studied. Data were analysed by different supervised and unsupervised multivariate statistical techniques in order to determine the most discriminant aroma volatiles analyzed by constant flow gas-chromatography mass-spectrometry that could be associated with differences in ripening and flesh firmness in non-climacteric melons. The NILs and the parental showed non-climacteric behaviour during ripening. SC10-2 was harvested at least 7 days later than the control. At harvest, only the NIL SC10-2 showed 65% higher flesh firmness than PS. Whole fruit hardness of SC7-1 was 34% lower than PS. The results obtained by the partial-least square discriminant analysis showed that the aroma better discriminated SC10-2 than SC7-1 from the control, with scarce differences between SC7-1 and PS. The aldehydes (Propanal, 2-methyl-) and the ketones (2-3 Pentanedione) were the most discriminating volatile groups among the NILs studied and PS. Higher levels of several aldehydes (Propanal, 2-methyl-, Benzaldehyde, 2,4-dimethyl-/Benzaldehyde, 3,4-dimethyl-, Butanal, 2-methyl-), not present in PS line, discriminated the NIL SC10-2 from the control PS. Also, SC10-2 displayed lack of some ketones (Acetophenone) and very low presence of alcohols (as for example, Cyclohexanol, 3,5-dimethyl-) compared with PS. The NIL SC7-1 was highlighted by higher relative content in alcohols (1-Octanol, 3-Ethyl-2-heptanol) and one acetate ester (Acetic acid, phenylmethyl ester) than PS and presence of ketones (2-3 Pentanedione, 2-Cyclopenten-1-one, 3,5,5-trimethyl-) that were absent in PS. The results are discussed in terms of the aroma biosynthesis pathways that could be affected by the introgressions.