Influence of Apple Cultivar and Canopy Position on Fruit Spur Leaf Development Within a Season

Abstract

Flowering and fruiting spur characteristics of ‘Granny Smith,’ ‘Lawspur Rome Beauty’ (‘Rome’) and ‘Redchief Delicious’ (‘Delicious’) apples ( Malus domestica, Borkh.) were examined at two canopy heights throughout a growing season. The first leaves (primary) to develop on the fruiting spur were distinguished from bourse leaves which developed later in the axils of primary leaves and which formed either a rosette of leaves or a short shoot. The primary leaf number/spur (LNO/SP) declined from about eight at full bloom (FB) to five at fruit harvest (FB + 160 days) with all three cultivars. Bourse LNO/SP increased from FB to FB + 104 days and was greatest for ‘Granny Smith’ and least for ‘Delicious.’ With each cultivar, bourse leaves had greater area/leaf (LA) and dry weight/leaf (LDW) than primary leaves. Development of primary leaf area/spur (LA/SP) and leaf dry weight/spur (LDW/SP) occurred from 7 days before FB to FB + 21 days. ‘Rome’ had greater primary LA/SP and LDW/SP than ‘Granny Smith’ and ‘Delicious.’ Bourse leaf development started at FB and continued to FB + 104. ‘Granny Smith’ and ‘Rome’ had much greater bourse LA/SP and LDW/SP than ‘Delicious.’ At fruit harvest leaf dry weight/leaf area (LDW/LA, specific leaf weight) was similar for primary and bourse leaves and cultivar differences were small. Cultivar effects were much greater than canopy position effects for all leaf traits except LDW/LA. Fruit dry weight was positively correlated with most bourse leaf traits with ‘Granny Smith’ but with ‘Delicious’ the correlations were poor except for LDW/LA.