Effect of gibberellic acid and uniconazol on embryo abortion in the stenospermocarpic grape cultivars Emperatriz and Perlon

Hypothesizing that seed abortion in stenospermocarpic grapes (Vitis vinifera L.) is caused by high gibberellin levels in the seed during the first stages of its development, we studied the effect of gibberellic acid GA3 and uniconazol (a GAs biosynthesis inhibitor) on this phenomenon. In vitro germination was analyzed in the seedless cultivars Emperatriz and Perlon, which were treated with 60 and 120 mg.-l 1 uniconazol (5 and 15 days before bloom) and 100 mg.-l 1 GA3 (5 days after bloom). In addition, endogenous levels of free gibberellins in flowers and seeds of Emperatriz and Perlon were compared with their seedeed progenitor Emperador. Clusters were harvested at bloom and 20 days after bloom for gibberellin analysis and at commercial maturity for in vitro culture of the seeds. Considerable gibberellin activity was found in the three cultivars, but only small differences were detected between the seedless and the seeded genotypes. Exogenous applications of GA3 had a deleterious effect on seed growth and on in vitro germination. Uniconazol also inhibited in vitro germination, though not affecting the total number of germinating embryos plus those rescued from non-germinating seeds. In conclusion, gibberellins do not appear to be directly involved in seed abortion of the stenospermocarpic cultivars Emperatriz and Perlon, although their participation in a more complex scenario should not be rejected, taking into account that in Perlon germination rates are positively correlated with the number of clusters per plant. Treatments with growth regulators also modified berry number per cluster, berry weight and rachis morphology. Finally, the plant source was a determinant affecting germination rates in vitro.