Performance of 'Braeburn', 'Golden Delicious' and 'Yataka Fuji' apple on Mark and M.9 rootstocks at multiple locations across North America

The performance of three apple (Malus x domestica Borkh.) cultivars ('Braeburn', 'Gibson Golden Delicious' and 'Yataka Fuji') on two dwarfing rootstocks (M.9 T337 and Mark) was studied for five years at multiple sites across North America as part of a large international cultivar evaluation trial. The trees were trained as slender spindles, and arranged in a randomized block design at each site. Cultural practices followed regional commercial recommendations, except that no calcium was applied. The effect of rootstock on cultivar performance was examined. Whether trees were propagated on Mark or M.9 made no difference to cultivar comparisons of the number of days between bloom and maturity, nor fruit red Color, soluble solids concentration, or length/ diameter ratio, but these measures were affected by location and/or location x cultivar interaction. Scion differences in bloom density ratings were consistent across all rootstocks and locations, with 'Braeburn' having the greatest bloom density, followed by 'Golden Delicious', and then 'Yataka Fuji.' Skin russet was unaffected by rootstock; 'Golden Delicious' had slightly more russet than 'Braeburn'. Rootstock affected flesh firmness consistently, with fruit from trees on Mark being about 0.27 kg firmer than on M.9. Rootstock differentially affected cultivar fruit size, flesh titratable acidity and yield efficiency. However, the cultivar x rootstock interaction effect was small compared to location differences for fruit size and yield efficiency, and its effect on fruit acidity was limited to one location. Rootstock influenced cultivar tree size (trunk cross-sectional area, tree height and spread), but the presence, direction and magnitude of the rootstock effect varied with location and cultivar. At sites and for scions where tree size differed significantly between rootstocks, trees on Mark tended to be larger than those on M.9 in sites with cold winters and smaller than on M.9 in southern sites. Rootstock also affected cumulative yield; the extent and direction of the effect varied with location but not cultivar. At the majority of locations, 'Golden Delicious' was more productive than 'Braeburn', but not more yield-efficient. At 13 of 19 locations, 'Golden Delicious' was more yield-efficient than 'Yataka Fuji'.