PRELIMINARY RESULTS ON INCREASING FRUIT SET IN OLIVES (OLEA EUROPAEA L.) BY CHEMICAL AND MECHANICAL TREATMENTS.

Fruit set in olive is normally very low compared to the high number of fertile flowers and plant potentiality. Several agronomical and chemical attempts have been made to improve yield on olive by reducing alternate bearing, fruit drop or increasing fruit set (Lavee, 1988). Often fruit set is affected by availability of nutrients or by a competition between reproductive and vegetative organs for their utilization (Sachs and Hackett, 1983). Both improvement of plant nutrition (by foliar and soil fertilization), and regulation of competition between reproductive and vegetative sinks may be possible (Klein and Weinbaum, 1984). Our goal was mainly to temporarily reduce vegetative growth favouring reproductive activity by Plant Growth Regulators (PGRs): Dichlobutrazole, Hexaconazole, Dikegulac and Abscisic acid (ABA).

The first two PGRs belong to the thriazole family: both are well known for their fungicide properties and for their easy uptake and translocation into the plant. Dichlobutrazole is also known to reduce size in ornamental plants (Pannelli, personal comun.), while other effects on endogenous phytormone balance are still not known (Davis et al., 1988; Grossmann, 1990). Dikegulac and ABA were tested respectively for their ability to temporarily block shoot elongation and for reduction of stomata aperture which both result in temporary growth reduction (Maag, 1984; Davies et al., 1979).