The Carbohydrate Balance of Alternate-bearing Citrus Trees and the Significance of Reserves for Flowering and Fruiting1

Abstract Two alternate bearing ‘Wilking’ mandarin ( Citrus reticulata Blanco) trees, an “on” and an “off” tree were uprooted and dissected into 11 organ types. Starch and soluble sugar concentrations were determined for each organ. Starch concentrations were 3.6 (leaves) to 17.4 (medium roots) times higher in the “off” tree. Soluble sugar concentrations were 1.5 (leaves) to 1.9 (medium roots) times higher in the “off” tree. A total dry matter, starch and soluble sugar balance was compiled for each tree. The “off” tree contained 13.26 kg starch and 10.66 kg soluble sugars; as against 2.95 kg starch and 6.75 kg soluble sugars in the “on” tree (excluding the fruit). The majority of this reserve pool would presumably be recycled and used for next year’s crop. Removal of fruit by mid-summer permitted reasonable flower bud differentiation the following year, connected with a build up of the starch reserve levels.