© 1995 Heron Publishing—Victoria, Canada
The effect of defruiting at different stages of fruit development on leaf photosynthesis of "Golden Delicious" apple
R. Gucci (1), >L. Corelli Grappadelli (2), S. Tustin (2, 3) and G. Ravaglia (2)
1. Dipartimento di Coltivazione e Difesa delle Specie Legnose, Sez. Coltivazioni Arboree, University of Pisa, Pisa, Italy / 2. Dipartimento di Colture Arboree, University of Bologna, Bologna, Italy / 3. The Horticulture and Food Research Institute of New Zealand, Havelock North Research Centre, Private Bag 1401, Havelock North,
New Zealand / Received March 4, 1994
Summary
Net photosynthetic rates (A) of leaves on 11-year-old, field-grown apple trees (Malus domestica Borkh. cv. Golden Delicious) were measured after removal of fruits at four different stages of development. Defruiting decreased
A by 21, 42, 27 and 7% when fruits were growing at 311, 293, 229 and 113 mgDW day–1, respectively. Photosynthesis was inhibited more in the afternoon than in the morning, but it was not affected during the
first 8 h after fruit removal. Inhibition of A was positively correlated with crop sink strength, but it was not correlated with fruit relative growth rate or crop load.
Defruiting decreased A at saturating irradiances (PPFD > 1000 µmol m–2 s–1), but did not modify the apparent quantum yield of single leaves. These results suggest that the overall effect of defruiting
on carbon fixation is negligible in dense canopies, but it may be significant in sparse canopies and in single shoots.
Keywords:
apparent quantum yield, fruit growth rate, Malus domestica, sink strength.
