Apple fruit growth and maturity are affected by early season temperatures

Container-grown 'Delicious', 'Golden Delicious', 'Braeburn', 'Fuji' and 'Ro yal Gals' apple [Malaus sylvestris (L,) Mill. var. domestica (Borkh.) Mansf ,] trees, on Malling 9 (M.9) rootstock, were subjected to a range of differ ent maximum/minimum air temperature regimes for up to 80 days after full bl oom (DAFB) in controlled environments to investigate the effects of tempera ture on fruit expansion, final fruit weight, and fruit maturation. Fruit ex pansion rates were highly responsive to temperature with those at a mean of 20 degrees C being approximate to 10 times greater than those at a mean of 6 degrees C. All cultivars exhibited the same general response although 'B raeburn' consistently showed higher expansion rates at all temperatures com pared with lowest rates for 'Golden Delicious' and intermediate rates for b oth 'Delicious' and 'Fuji'. The duration of cell division, assessed indirec tly by measuring expansion rate, appeared to be inversely related to mean t emperature (i.e., prolonged under cooler conditions). Subsequently, fruit o n trees from the coolest controlled temperature treatment showed greater ex pansion rates when transferred to the field and smaller differences in frui t size at harvest than would have been expected from the measured expansion rates under the cool treatment. Nonetheless, mean fruit weight from warm p ostbloom treatments was up to four times greater at harvest maturity than t hat from cool temperature treatments. Postbloom temperature also markedly a ffected fruit maturation. Fruit from warm postbloom temperature conditions had a higher soluble solids concentration, more yellow background color, lo wer flesh firmness, and greater starch hydrolysis than fruit from cooler te mperatures.