Quality attributes during maturation of ‘Golden Delicious’ and ‘Red Delicious’ apples grown in two geographical regions with different environmental conditions

Apples have distinctive quality attributes that may be defined by environmental conditions of the geographical regions where fruits are cultivated, such as temperature, solar radiation, photoperiod, and photothermic units. A three-year study was conducted to compare ‘Golden Delicious’ and ‘Red Delicious’ apples from two different regions, Washington, USA (WA) and Chihuahua, Mexico (CHIH). Apple samples were harvested weekly from early August to late October (~120-180 days after full bloom - DAFB), and analysed for quality parameters. Geographic environmental data were obtained, and photoperiod, solar radiation, degree-days and photothermal units were calculated. Results show quality differences between CHIH and WA apples. WA shows a ~5-week delay in apple bloom, possibly due to the lower temperatures presented in WA. Apples from both regions required the same photoperiod, ~ 2,222 h, to attain the beginning of the ripening stage, which took more days (three weeks) for CHIH apples, most likely attributed to the higher elevation of CHIH orchards (2,062 vs. 763 masl). The main distinctive quality differences found between WA and CHIH apples were firmness and aroma volatile compounds. CHIH apples presented substantially higher amounts of aroma compounds. WA apples showed greater firmness, probably due to lower photothermal units. Using all firmness data (both varieties, both growing zones) a remarkable correlation was found between firmness and photothermal units (R=0.89), which may suggest firmness could be improved by the manipulation of degree days and photoperiod, that is, temperature and light.