Abstract: High temperature during fruit expansion is an important environmental factor affecting the quality of Newhall navel orange in southern Jiangxi Province. It is important to analyze the effects of high temperature on the quality of Newhall navel orange and construct a high-temperature impact evaluation index for the assessment of climatic quality of Newhall navel orange. In this study, based on multi-year quality data of Newhall navel oranges in seven main producing counties (districts) of southern Jiangxi Province and the meteorological data, we analyzed the effects of high-temperature days and accumulated heat of mean high temperature (i.e., daily mean temperature ≥30 ℃), daytime high temperature (i.e., daily maximum temperature ≥35 ℃) and nighttime high temperature (i.e., daily minimum temperature ≥24 ℃) during fruit expansion on solid-acid ratio, single fruit weight and vitamin C of Newhall navel oranges by correlation analysis. The fluctuation models of solid-acid ratio, single fruit weight and vitamin C were established by multiple stepwise regression and probability distribution fitting, and the threshold value of high temperature effect of each quality factor was determined. Finally, the high-temperature impact evaluation index (HIEI) was established by the weighted summation of the fluctuation model of each quality factor, of which the weight coefficients of each quality factor was determined by the analytic hierarchy process (AHP) method. Results showed that the effects of high temperature during fruit expansion on the quality of Newhall navel oranges were stage-dependent. High temperature in June significantly increased the solid-acid ratio and vitamin C content (P<0.05) and showed a weak positive correlation with single fruit weight (P>0.05). High temperature from July to September was negatively correlated with solid-acid ratio and single fruit weight, with a negative correlation between nighttime high temperature days and vitamin C content (P<0.01). The determination coefficient (R²) of each quality factor fluctuation model was between 0.51-0.81, and the quality fluctuation simulated by the model could well reflect the actual measured fluctuation. The thresholds of the HIEI of mild, moderate and severe levels were -7 to 0, -13 to -7, and <-13, respectively.

Key words: Newhall navel orange, quality factor, high-temperature parameter, response model, construction of evaluation index, impact level.