Influence of berry growth and growth regulators on the development of grape peduncles in Vitis vinifera L.

Removal of grape berries (cv. Roter Gutedel) after setting (10 d after anthesis) had just a slight effect on the subsequent health of the peduncle. But if younger berries of flowers were removed before this stage the peduncle formed abscission layers along its length, and/or it died. Treatment of deflowered peduncles with a-naphthalene acetic acid (NAi\) prevented peduncle abscission and death; it is suggested that auxins produced by flowers have a hormonal role in maintaining normal development of the peduncle. Treatment with 2-chloroethyltrimethyl ammonium chloride (CCC), benzyladenine (BA), indole-3-acetic acid (IAA) or 3-indolebutyric acid (IBA) did not give these effects. The lack of effect of the latter two compounds (auxins) is possibly due to their catabolism. Treatment with gibberellic acid (GA) resembled NAA in that it also maintained the health of deflowered peduncles, but GA had the additional effect of causing prolonged development of metaxylem. Gibberellin produced by developing berries may also have a hormonal role in peduncle development. The occurrence of grape peduncle necrosis (stiellaehme), which appears associated with a gibberellin deficiency during setting, supports this idea.