Field non-destructive determination of nectarine quality under deficit irrigation

This study investigated the effects of deficit irrigation (DI) at different fruit growth stages and tree orientation on fruit quality of 'September Bright' nectarines (Prunus persica L. Batsch). Control trees were fully irrigated throughout the entire fruit development period, whereas deficit irrigation was supplied at fruit growth stage I (cell division, DI-I), II (pit hardening, DI-II), IIIa (cell expansion, DI-IIIa) and IIIb (fruit maturation, DI-IIIb). Non-destructive measurements of fruit maturity and quality were carried out using portable devices based on near-infrared spectrometry and pigment fluorescence on west- and east-oriented trees of an Open Tatura system. Chlorophyll degradation (index of absorbance difference, I-AD), soluble solid concentration (SSC), dry matter percentage (DM), anthocyanin (fluorescence excitation ratio anthocyanin relative index, FERARI) and flavonol concentrations (FLAV) were measured in the four weeks prior to harvest. Yield, crop load, fruit weight and diameter, flesh firmness, and skin dark red and light red coverage were measured at harvest. DI-I, DI-IIIa and DI-IIIb caused a significant reduction of fruit size and yield. I-AD and FERARI declined progressively towards fruit maturity but were not significantly influenced by irrigation. FLAV remained stable until harvest despite a short-term response to water deficit at the beginning of stage IIIb before returning to its previous value. Fruit SSC and DM were highest in DI IIIb and DI I, respectively, and similar to control in DI II and DI IIIa. Tree orientation did not affect fruit quality, except for higher I-AD and FLAV in west- compared to east-oriented trees. Overall, all the DI-treatments induced a crop performance loss, even though different crop parameters were affected, with DI-IIIa causing the most detrimental effect on fruit quality. The non-destructive devices proved useful in determining fruit quality in situ.