APPLE FRUIT REMOVAL AND LIMB GIRDLING AFFECT FRUIT AND LEAF CHARACTERISTICS

Mature apple trees (Malus domestica Borkh.) were studied in 1989 and 1 990 to explore the effect of crop load on fruit dry weight (DW), dry-m atter concentration (DMC), specific leaf area (SLA), and leaf C exchan ge, using girdled (G) and nongirdled (NG) limbs. Fruit DW and DMC decr eased with heavier fruit loads. Fruit on G limbs had higher fruit DW a nd DMC than on NG limbs. SLA on NG limbs was unaffected by crop load, but increased dramatically on G limbs with a crop load of less than on e fruit per square centimeter limb cross-sectional area. These leaves also had a low photosynthetic rate, high stomatal resistance, and high internal CO2 concentration. The results do not support the concept of feedback inhibition of photosynthesis and demonstrate specific circum stances in which the capacity of sinks to use assimilates was saturate d. Exceeding this limit by significantly reducing sink strength result ed in excessive carbohydrate accumulation in leaves. Nutrient levels i n leaves on G, nonfruiting limbs were generally lower than for the oth er treatments.