Abscission olives

Anatomy of the abscission zone at the base of mature fruits has been investigated in apples (10), cherries (11), citrus (12), and olives (13) and has been discussed as related to mechanical fruit removal (2, 14), The histochemistry of the separation layer of mature fruit is very similar to that of leaves of citrus (15) and bean (16,17), The actual separation occurs through one or more processes in the separation zone (a) a weakening of the cementing ability of the middle lamella between cells, and (b) a softening of the entire cells (17), In some plants, the abscission zone is structurally differentiated as a layer of compact cells or as a zone of localized cell division in other species, abscission may occur across a transect of cells which show little or no visible diflFerentiation (18). Thus, major components of the separation process involve the dissolution of middle lamella and lysis of cell walls or entire cells in the separation zone, but this is not necessarily associated with distinctive morphological characteristics (19). 

Ethephon has received the most attention for use in loosening fruit as an aid to mechanical harvesting. Various degrees of success have been obtained using ethephon on olives (78, 79, 80), blueberries 81), cherries 82-86), plums (87), peaches (88, 89), and apples (90, 91, 92, 93). The initial visible fruit response is an increase in coloration, but higher concentrations do result in abscission of the fruit. 

Cycloheximide (CHI), when applied directly to separation zones, will inhibit abscission of citrus fruit explants 24) as it does bean petiole explants (29). By application to citrus fruit surfaces, the rind is injured, evidenced as small pitted areas, and ethylene is produced in quantities that accelerate the abscission processes (41). Apparently, CHI applied to the fruit wall enhances the senescence processes, including ethylene production, thereby stimulating citrus fruit abscission via ethylene production and not by action directly on the tissues in the separation zone (41). Cycloheximide has also been used for harvest of olives (80, 103) and apples (104). 

Olive trees, cv Picual, some 25-30 year-old, were used. Some branches were defoliated eight weeks after flowering, when the period of physilogical fruit abscission was over and before the lignification of the endocarp and the onset of oil accumulation in the mesocarp. At the same time selected fruits were enclosed in specially designed dark cages to procure non-photosynthetic conditions for the development of the encaged olive (Sanchez, 1995). 

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