Isolation of molecular markers for the evaluation of quality in pre-harvest and postharvest stages in rocket and melon

The development of rapid, reliable and specific methods are necessary for the evaluation of quality in ready-to-eat vegetables during the production chain from pre- to post-harvest and storage stages. Since the quality after harvest cannot be improved but only preserved, quality markers must be isolated in order to identify the minimum variation of quality already after the first day of storage. Our objective was to identify stress responsive genes that are associated with quality losses and can be used as quality markers in both rocket (Diplotaxis tenuifolia L.) and melon (Cucumis melo L.) fresh cut produce. Quality markers were isolated by transcriptome sequencing (RNA-Seq) analysis in rocket. Rocket plants were grown using hydroponic systems in controlled growth chambers for 3 weeks prior to stress treatment. In pre-harvest was imposed salinity (200 mM NaCl), heat radical stress (40°C), nitrate deficiency (absence of NH4+/NO3-), while in post-harvest was imposed chilling (4°C), wounding, dark and water stress. Sampling was performed after 24 hours and total RNA was extracted from stressed and control plants and sequenced with a two paired-end Illumina sequencing approach. Bioinformatics analyses identified interesting candidate genes that encoded proteins associated with senescence, degenerative processes and quality loss and that showed an up-regulation in all the stresses. The identification of molecular markers in melon was performed by searching for the homologous genes of the putative markers identified in rocket. The expression levels of these quality markers was analyzed by quantitative PCR (qPCR) at different time points from harvest to 14 days of storage at 20°C (stress) and 4°C (control) in rocket and melon produce. Real-time analyses showed that in both species all genes increased their mRNA abundance soon after the harvest until the 3rd day of storage (at 20°C) and until the 11th day of storage (at 4°C). These results show that senescence associated markers will be useful to evaluate the quality of the produce during shelf life.