Effects of gibberellic acid, asparagine and glutamine on flower bud induction in olive

In 1992, the following treatments were applied to olive trees, cv. Maurino, which had average flowering: removal of 50% and 100% of the flowers in mid-June, leaf treatment with gibberellic acid (GA(3)) at 60 ppm in mid-July, at the end of August, in mid-October and in July, August and October, leaf treatment with paclobutrazol (PP333) at 1000 ppm at the end of October, treatment of the soil with asparagine (10(-5) M) and glutamine (10(-5) M) at the end of December. Thinning and complete removal of the blossoms stimulated vegetative activity. Treatments with GA(3) in July slightly increased vegetative growth in both the treatment year and the following year, while the later treatments and those with asparagine and glutamine stimulated growth only in the following year. PP333 reduced plant growth in the year following treatment. The complete or partial removal of the olive blossoms strongly increased flowering and fruit production in the year following treatment. Treatment with GA(3) and PP333 did not significantly influence flowering or fruit production in the following year. Application of asparagine and glutamine positively influenced the induction process without affecting production per tree. Therefore, GA(3) and other hormonal substances seem not to have a direct influence on flower bud induction but rather, induction is mediated by their effects on the availability and distribution of the assimilates. Asparagine and glutamine may be involved in the inductive process as messengers in relation to the food reserves in the plant.