Relationships between Stem Length, Leaf Area, Stem Weight, and Accumulated Growing Degree-days in Apple Shoots

The relationship of leaf area and stem weight, with stem length at different times during the year, was studied on 5 apple ( Malus domestica Borkh.) cultivars. Leaf area was related linearly to stem length, but the slope differed by up to 2-times between cultivars. Stem dry weight increased curvilinearly with respect to stem length and showed less variation among cultivars than did leaf area. These 2 relationships combined indicated that the stem constitutes an increasing proportion of the total shoot weight with increasing stem length. Dormant stems had a greater weight per unit length than stems of growing shoots. Both stem length and leaf area showed strong fitting linear relationships with accumulated growing degree-days, but the stem length relationship showed less variability among cultivars than did leaf area.