Effects of irrigation on fruit ripening behavior and metabolic changes in olive

Abstract

Olive (Olea europaea, cv Leccino) fruits grown under different water regimes were analyzed by metabolomics and specific transcript accumulation analyses. The fruit from non-irrigated (rain-fed) and irrigated trees cultivated under field conditions, with a seasonal water amount equivalent to the calculated crop evapotranspiration (ETc) was compared in the last developmental phase and, in particular, at commercial harvest. Metabolomics (GC–MS) analysis identified several hundred metabolites in ripe mesocarp, 46 of which showed significantly different contents in the rain-fed and irrigated samples. Some compounds involved in primary metabolism (carbohydrates, amino acids, organic acids) and secondary metabolism (squalene, simple phenols) appeared to be more abundant when irrigation was performed. Higher levels of total polyphenol were observed in the rain-fed fruit, which at ripening showed an increase in anthocyanin concentration. These data indicate that ripening in olives is affected by irrigation. In addition, expression analyses of three key polyphenol biosynthetic genes (phenylalanine ammonia lyase (PAL), chalcone synthase (CHS), dihydroflavonol reductase (DFR)) and two genes involved in triterpenoid metabolism (β-amyrin synthase and cycloartenol synthase) were also performed. The analyzed genes showed different expression patterns throughout ripening, and the resulting PAL, DFR and β-amyrin synthase transcript accumulation was found to be affected by the different water regimes at specific stages of fruit development.