Abstract

Sun-injury (=sunburn) on apples, as well as in other species, is a physiological disorder that develops in thefield when high irradiance combines with elevated temperature during the growing season. This causesphotooxidative and heat stress that finally leads to symptoms in sun-exposed fruit tissue. The objectiveof this study was to assess metabolite profiles changes, as a consequence of these abiotic stresses, usingVIS/NIR reflectance in Granny Smith apples. Individual fruit was tagged and weekly monitored from60 until 151 DAFB. Vis/NIR reflectance measurements (350–1100 nm) were taken on the fruit surfaceon apples unexposed to direct sunlight (NE, class 0), exposed to direct sunlight (EX, class 1) and thosethat developed sunburn in the categories of Mild (class 2), Moderate (class 3), and Severe (class 4).Spectral curves were analyzed using discriminant partial least square models (PLS-DA) and interval PLSdiscriminant analysis (iPLS-DA). PLS-DA analysis was able to separate fruit with and without visiblesun injury with a classification error of 22.5% and 35.7% for class 3 and 2, respectively. Class 3 and 4observed at 129 DAFB was predicted through reflectance spectra captured 87 DAFB by PLS-DA, with550–570 nm, 715–750 nm, and 810–850 nm spectral intervals responsible ranges for discrimination. Suchchanges in Vis/NIR reflectance among classes would be related to changes in pigments (carotenoidsand flavonoids) and apple tissue structural properties. These findings indicate that the method offerspotential for nondestructive prediction of sunburn occurrence on apples in the orchard, that could leadto development of an automated system to forecast sunburn occurrence.