Spur Leaf Characteristics of Nine Apple Cultivars

Abstract

Spur leaves are important in many aspects of fruit development. They are the first leaves to emerge from dormant buds of bearing apple trees, and comprise the majority of the tree canopy until shortly after bloom. Hansen (5) has indicated that the new leaves provide the "greater part by far" of photosynthates for the growth of fruit compared to carbohydrates mobilized from reserves. The removal of the spur leaves prior to or during bloom reduces fruit set (1). From a 3-year survey of more than 50 blocks of Delicious trees in major apple producing regions, Dennis (2) found that total solar radiation during the 3 week period prior to and during bloom correlated significantly with fruit set. Spur leaves comprise nearly the entire tree canopy during this critical period for fruit set and cell division and exert an important localized influence on fruit size, shape and calcium level that are important for quality and storage (3). A minimum spur leaf area is necessary for flower bud formation (6). Thus, many studies have indicated the vital role of spur leaves for fruit development, but the influence of various cultivars on spur leaves and other spur characteristics has not been well documented.