Effect of the bearing condition of the tree and defoliation on the dormancy onset and release of olive buds

Leafy and defoliated 3-node cuttings of 'Manzanilla de Sevilla' olive were obtained in the field from June 1996 until February 1997 and forced for budburst in a growth chamber at 20 degrees C. Defoliation increased budburst of cuttings taken from both bearing (ON) and non bearing (OFF) trees, although the budburst pattern differed. In OFF defoliated cuttings, there was a steady decrease in budburst from June to December, except in September when budburst increased. In February, defoliation had no effect and there was a sharp increase of budburst due to inflorescence development. In ON defoliated cuttings, there was a variable but relatively uniform budburst trend and a small final inflorescence development. Reproductive budburst was only observed after chilling accumulation. Forcing temperatures influenced the time and duration of reproductive budburst: 12.5 degrees C promoted earlier and slower budburst and 30 degrees C later and faster budburst comparing with 20 degrees C. Anatomical observations confirm a differential behavior in ON and OFF development after sufficient chilling accumulation. Dormancy and release from dormancy of OFF buds appears to be a prerequisite for inflorescence development.