This study aimed to understand the effects of meteorological factors on the 'Fuji' apple quality in the Circum-Bohai and Loess Plateau apple production regions of China and to guide apple production based on local climate. Fruit samples of the 'Fuji' apple and meteorological data were investigated from 132 commercial 'Fuji' apple orchards covering 44 counties in the two aforementioned production regions (22 counties per region). The partial least-squares regression (PLSR) method was first used to screen major meteorological factors that greatly affected fruit quality; these were subsequently used to establish the regression equation of fruit quality attributes and major meteorological factors. Linear programming was used to estimate optimum meteorological factors for good apple quality. The results showed that in the Circum-Bohai production region, many meteorological factors (total annual precipitation, total precipitation from April to October, lowest temperature from April to October, sunshine percentage from April to October) were significantly higher than those in the Loess Plateau production region; however, the temperature difference between day and night from April to October was significantly smaller than that in the Loess Plateau production region. The soluble solids content and skin color area of apples from the Loess Plateau production regionwere significantly greater than those from the Circum-Bohai production region. The same fruit quality factor of 'Fuji' apple was affected by different meteorological factors in the two production regions. The monthly mean temperature and monthly highest temperature from April to October of the Circum-Bohai production region had relatively larger positive effect weights on fruit quality, whereas the total annual precipitation, monthly mean relative humidity from April to October, and total precipitation from April to October of the Loess Plateau production region had relatively larger positive effect weights on fruit quality. The major influencing meteorological factors of the fruit soluble solids content were total precipitation from April to October (X-7), mean annual temperature (X-1), and the monthly highest temperature from April to October (X-5) in the Circum-Bohai production region; however, it included the monthly mean temperature difference between day and night from April to October (X-6), total annual precipitation (X-2), and total precipitation from April to October (X-7) in the Loess Plateau production region. In the Circum-Bohai production region, the optimum meteorological factors for 'Fuji' fruit quality of vigorous apple orchards were the mean annual temperature (13.4 degrees C), total annual precipitation (981 mm), monthly mean temperature (16.8 to 22.4 degrees C), lowest temperature (11.9 degrees C), highest temperature (19.5 to 26.8 degrees C), temperature difference between day and night (12.3 degrees C), total precipitation (336-793 mm), relative humidity (55.7% to 70.7%), and sunshine percentage (42.3% to 46.1%) during the growing period (April-October). In the Loess Plateau production region, the optimum meteorological factors for 'Fuji' fruit quality of vigorous apple orchards were the mean annual temperature (5.5 to 11.6 degrees C), total annual precipitation (714 mm), monthly mean temperature (13.3 to 19.9 degrees C), lowest temperature (7.9 to 9.3 degrees C), highest temperature (19.6 to 27.3 degrees C), temperature difference between day and night (7.1 to 12.4 degrees C), total precipitation (338-511 mm), relative humidity (56. 1% to 82.4%), and sunshine percentage (37.3% to 55.9%) during the growing period (April-October). The restrictive factors for high-quality 'Fuji' apples of the Circum-Bohai production region were the smaller monthly mean temperature difference between day and night, higher monthly mean lowest temperature, and larger monthly mean relative humidity during the growing period; however, those of the Loess Plateau production region were drought or less precipitation from November to March, lower monthly mean temperature, and higher monthly mean highest temperature during the growing period.
