Cultivar and Canopy Position Effects on Seasonal Development of Vegetative Spurs of Apple

Abstract

Vegetative (nonflowering) spur characteristics of `Granny Smith', `Lawspur Rome', and `Redchief Delicious' apples (Malus domestics Borkh.) at two canopy positions (1 and 2 m heights) were examined on eight dates throughout a growing season. `Granny Smith' had a greater leaf number/spur (LNO/SP) at each date than `Rome' and `Delicious'. Area/leaf (LA) and dry weight/leaf (LDW) for `Delicious' were substantially less than for `Granny Smith' and `Rome'. Area/leaf increased rapidly after full bloom (FB) until FB + 21 days for `Delicious', FB + 35 for `Granny Smith', and FB + 56 for `Rome', after which no further changes occurred. For each cultivar, leaf area/spur (LAMP) and leaf dry weight/spur (LDW/SP) increased rapidly from FB until FB + 35 days and then more gradually until FB + 104 days. From FB + 21 onward, `Granny Smith' had greater LA/SP and LDW/SP than `Rome', which, in turn, was greater than for `Delicious'. At harvest (FB + 160), LA/SP was 2.5-fold greater for `Granny Smith' and 1.7-fold greater for `Rome' than for `Delicious'. Cultivar differences for leaf dry weight/leaf area (LDW/LA) were small and canopy position differences were large. LDW/LA declined from 7 days before FB to FB + 7, then gradually increased to the end of the season. Dry weight of the vegetative spur buds (with leaves removed) was lower for `Delicious' than for `Rome' or `Granny Smith'. Total spur dry weight (bud + leaves) was, from FB + 21 onward, greatest for `Granny Smith', intermediate for `Rome', and lowest for `Delicious'.