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 vinifer a L.) is caused by high gibberellin levels in the seed during the first sta ges of its development, we studied the effect of gibberellic acid (GA(3)) a nd uniconazol (a GAs biosynthesis inhibitor) on this phenomenon. In vitro g ermination was analyzed in the seedless cultivars Emperatriz and Perlon, wh ich were treated with 60 and 120 mg.l(-1) uniconazol (5 and 15 days before bloom) and 100 mg.l(-1) GA(3) (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 harves ted at bloom and 20 days after bloom for gibberellin analysis and at commer cial maturity for in vitro culture of the seeds. Considerable gibberellin a ctivity was found in the three cultivars, but only small differences were d etected between the seedless and the seeded genotypes. Exogenous applicatio ns of GA(3) had a deleterious effect on seed growth and on in vitro germina tion. Uniconazol also inhibited in vitro germination, though not affecting the total number of germinating embryos plus those rescued from non-germina ting seeds. In conclusion, gibberellins do not appear to be directly involv ed in seed abortion of the stenospermocarpic cultivars Emperatriz and Perlo n, although their participation in a more complex scenario should not be re jected, taking into account that in Perlon germination rates are positively correlated with the number of clusters per plant. Treatments with growth r egulators also modified berry number per cluster, berry weight and rachis m orphology. Finally, the plant source was a determinant affecting germinatio n rates in vitro.