In vitro studies of ABA and ethephon induced abscission in olive organs

Abstract

SummaryDetached reproductive shoots of olive (Olea europaea L. cv. Konservolia) were basally fed continuously with solutions of 25 ppm (0.10 mM) or 50 ppm (0.19 mM) abscisic acid (ABA) and 25 ppm (0.17 mM) or 50 ppm (0.32.mM) (2-chloroethyl)phosphonic acid (ET) individually or in combination, four weeks before full bloom. Leaf and flower abscission were counted along shoots at 24 h intervals over a 120 h period. A lag period of 72 h was needed for the first abscission of both organs in the control (water). By 120 h leaf abscission in control remained low (about 15%), although flower abscission was four-fold higher (about 60%). All treatments with growth regulators reduced the lag period for the first leaf and flower abscission to 48.h. Individual ABA or ET applications resulted in a very low leaf abscission at 48 h treatment. The effect was increased by increase in both concentration and application period, attaining maximum values after 120.h (60–95%). The combination of ABA and ET at both levels showed a synergistic effect on leaf abscission, resulting in a considerable abscission at 48 h and an almost complete leaf shedding even after 96.h application time (90–95%). After 48 h treatment, a separation layer was developed in petioles of seventh node sections only in the combined application of ABA and ET at 50 ppm level. ET was continuously more effective than ABA on olive flower abscission. Both concentrations of individual ABA treatments showed similar effects on olive flowers, over all the examined periods. The combined ABA and ET applications were more effective than single ones on flower abscission. Profiles of leaf and flower abscission showed decreasing trends from the basal to the upper nodes of shoots in all treatments, but the effect of combined applications extended with higher rates to the top of the shoot. Statistically significant differences in leaf and flower abscission were found among treatments, as well as among different node positions over all the experimental time. Our results showed the combination of ABA and ET to be very effective for olive leaf abscission.