Alternate bearing in olive
Alternate bearing (AB), a low-yield off crop (OFF tree, OFF year) followed by a high-yield on crop (ON tree, ON year), is initiated in perennial tree crops by adverse climate events that occur during bloom or fruit set and affect not only the crop trees, but also the pollinizer trees, causing poor flowering, reduced pollination and fruit set, or excessive flower and fruit drop. The result is an OFF crop that is typically followed by an ON crop. Conversely, optimal climate conditions during bloom and fruit set such that normal crop thinning fails to take place result in an ON crop, which is followed by an OFF crop. Globally, AB is a serious economic problem for oil and table olive growers. In OFF years, trees produce large fruit but too few to provide a good income. In ON years, trees produce a large number of small fruit of reduced commercial value that take longer to mature, attain size and accumulate oil. The delayed harvest exacerbates AB. For 'Manzanillo' olive (Olea europaea L.) in California, our results documented that the setting ON crop reduced spring and summer vegetative shoot growth, thereby reducing the number of nodes that could bear inflorescences the following spring. The ON crop further reduced floral intensity by inhibiting spring bud break. The negative effects of the ON crop of fruit on summer vegetative shoot growth and spring bud break were partially mitigated with cytokinin plant growth regulators.
Fichtner, E.J. and Lovatt, C.J. (2018). Alternate bearing in olive. Acta Hortic. 1199, 103-108
ON-crop tree/year, OFF-crop tree/year, vegetative shoot growth, spring bud break, plant growth regulators, auxin-transport inhibitor, cytokinin