Influence of Rootstock on ‘Delicious’ Apple Fruit Shape

Abstract

Differences in scion growth, measured as trunk cross-sectional area (TCA), were observed for trees on 32 apple rootstocks during two seasons. M.27 EMLA (E), P.16, V.3, and P.22 were the least vigorous rootstocks and P.18, A.313, and seedling the most vigorous. Fruit length/diameter (L/D) ratio, a measure of fruit elongation and typiness, for ‘Starkspur Supreme’ and 'Redchief (Campbell) Delicious’ varied with rootstocks and season. Fruit were more elongate during a growing season that was cooler among the two seasons. The relationship between rootstock vigor and fruit L/D ratio was curvilinear with both ‘Delicious’ strains in both seasons. Trees on the most dwarfing rootstocks M.27E and P.16 had the lowest fruit L/D ratio. As rootstocks increased in vigor from extremely dwarf to semidwarf, e.g., M.7, fruit L/D ratio was higher. Fruit L/D ratio for rootstocks more vigorous than M.7, e.g., P.18 and seedling, was similar to that for semidwarf rootstocks. Rootstock accounted for 40 to 83% of the variation in fruit L/D ratio, depending on the season and ‘Delicious’ strain.