BACKGROUND: A near-isogenic line (NIL) of melon (SC10-2) with introgression in linkage group X was studied from harvest (at firm-ripe stage of maturity) until day 18 of postharvest storage at 20.5°C together with its parental control ('Piel de Sapo', PS). RESULTS: SC10-2 showed higher flesh firmness and whole fruit hardness but lower juiciness than its parental. SC10-2 showed a decrease in respiration rate accompanied by a decrease in ethylene production during ripening, both of which fell to a greater extent than in PS. The introgression affected 11 volatile organic compounds (VOCs), the levels of which during ripening were generally higher in SC10-2 than in PS. Transcriptomic analysis from RNA-Seq revealed differentially expressed genes (DEGs) associated with the effects studied. For example, 909 DEGs were exclusive to the introgression, and only 23 DEGs were exclusive to postharvest ripening time. Major functions of the DEGs associated with introgression or ripening time were identified by cluster analysis. About 37 genes directly and/or indirectly affected the delay in ripening of SC10-2 compared with PS in general and, more particularly, the physiological and quality traits measured and, probably, the differential non-climacteric response. Of the former genes, we studied in more detail at least five that mapped in the introgression in linkage group (LG) X, and 32 outside it. CONCLUSION: There is an apparent control of textural changes, VOCs and fruit ripening by an expression quantitative trait locus located in LG X together with a direct control on them due to genes presented in the introgression (CmTrpD, CmNADH1, CmTCP15, CmGDSL esterase/lipase, and CmHK4-like) and CmNAC18.

A methodology for making consistent studies of outliers of non-climacteric melon volatile organic compounds at harvest is reported. The juice was squeezed from the fruit of the 'Piel de sapo' cultivar harvested during two consecutive seasons and the aroma volatiles were extracted by headspace solid phase microextraction and measured by gas chromatography coupled to mass-spectrometry. A deconvolution analysis was performed to obtain volatile organic compounds. For multivariate the reliable identification of outliers, compound classes were studied as a percentage of total area counts of the melon compounds identified in the chromatogram by principal component analysis and partial least-squares discriminant analysis, and then verified by correlation analysis, box-whisker plot, and formal tests for univariate outliers. Principal component analysis was the key methodology for selecting outliers in variables that mostly did not follow a normal distribution. The presence of an excess in terms of relative percentage of area and the diversity of minor compounds such as alcohols, terpenes, acids, among others, are usually a sign of anomalous data that can be considered outliers in the aroma of this non-climacteric cultivar. This multivariate approach removed outliers, but kept the variability of aroma among the samples of every cultivar.

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