LAUSR

BACKGROUND Consumers of grapefruit require consistent fruit quality with a good physical appearance and taste. The air temperatures during the growing season affects both the external (external color index ECI) and internal (titratable acidity TA and total soluble solids ratio TSS/TA) fruit quality of grapefruit. The objective of this study was to develop computer models that encompass the relationship between preharvest air temperature and fruit quality to predict fruit quality of grapefruit at harvest. RESULTS There was a logarithmic relationship between the number of days with a daily minimum air temperature ≤ 13°C and ECI, with a greater number of days resulting in higher ECI. In addition, there was a second-order polynomial relationship between the number of hours ≥ 21°C and both TA and TSS/TA, with a greater number of hours resulting in lower TA and higher TSS/TA. Model performance for predicting the ECI, TA and TSS/TA during 2004-05 and 2005-06 growing seasons was good, with Nash and Sutcliffe coefficient of efficiency (NSE) values of 0.835 and 0.917 for ECI, 0.896 and 0.965 for TA and 0.898 and 0.966 for the TSS/TA, respectively for each season. Applying the model to statistical survey data covering 13 growing seasons demonstrated that the TSS/TA model was robust. CONCLUSION Statistical models were developed that predicted the development of grapefruit ECI, TA and TSS/TA. The TSS/TA model was confirmed after application to long-term statistical survey data covering 13 growing seasons. This article is protected by copyright. All rights reserved.