Discriminant models development for abiotic stress-related physiological disorders on apples based on visible-near-infrared reflectance spectroscopy
Keywords: abiotic stress, Vis-NIR, pome fruit, post harvest
Apple production in Chile, as in many other semi-arid production regions in the world, occurs inareas with stressful climatic conditions during the growing season. This, not only leads to ‘stress-related symptoms’ on the fruit that appear pre-harvest, such as sunburn, but also to postharvest disorders and erratic maturity behavior. Among postharvest physiological disorders caused by abiotic stress (high irradiance, elevated temperature, etc.), sunscald and flesh Browning (FB) have important economic implications for growers and packers. Sunscald (i.e. delayed sunburn) symptoms (dark brown patches) appear only on the sun-exposed section of the fruit during low temperature storage. Flesh Browning is commonly observed in many apple cvs, including Cripp’s Pink. These symptoms appear in cortex tissue (i.e. flesh) as diffuse or defined brown (oxidized) patches in part or all around the flesh during cold storage. Although both disorders mentioned earlier have different origin and symptoms expression, they both have antioxidant metabolites and specific regulatory metabolites associated with their expression postharvest. Along with metabolomics studies to understand the origin of sunscald and FB, it would be faster and more efficient, to test the correlation of these metabolites with non-destructive spectral techniques, such as UV/Vis/NIR spectroscopy. The development of such models could be critical to understand how preharvest factors (and stress events) affect postharvest physiological disorders development. The latest is key to, in the future, predict fruit behavior and quality based on growing conditions in the field that imprints on metabolomics.The objectives of the current proposal are: - To correlate antioxidant metabolites, such as ascorbic acid, glutathione, and specific phenolics involved in sunscald development on apples cv. Granny Smith, with pre-and-post harvest UV-Vis/NIR spectral tissue fingerprint. - To correlate specific metabolites (antioxidants, growth regulators) with flesh browning appearance in apples cv. Cripp’s Pink, and pre-and-post harvest spectral tissue fingerprint. - To correlate spectroscopy measurements on apple skin (external) during its growth on the tree with FB appearance during cold storage, and - to study predicted model’s performance over two storage temperature regimes with differential expression of FB. To accomplish this two experiments will be set up. The first one will address sunscald development. Granny Smith apples will be sampled sequentially from 60 days after full bloom until 5 months following cold storage every 15 days. Five replications per sunburn category of 10 apples each will be used for reflectance measurement and metabolic profiling (antioxidant metabolites, phenolics, aminoacids). Sunscald appearance postharvest will be monitored. The second experiment will address flesh browning development. In this experiment Cripp’s Pink apples will be samples 60 days after full bloom until 5 months following cold storage every 15 days. As in sunscald, five replications of 10 apples each will be used for reflectance measurement and metabolic profiling (antioxidant metabolites, sugars, and amino acids, ATP.). This time a correlation of external and internal reflectance will be obtained. The expected results are development of spectral tissue fingerprinting for sunscald and flesh browning, and their metabolic changes, that could be used as a tool to predict, via discriminant models, the appearance of both disorders during cold storage.
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