EFFETTI DEL PACLOBUTRAZOLO (PP333) SU PIANTE DI NOCCIOLO SOTTOPOSTE A POTATURA DI RICOSTITUZIONE

A trial was carried out in 1988 to 1990 in a 17-year-old hazelnut orchard of "Tonda Romana" with trees spaced 4x2m. The plants trained to vase on a medium textured soil were subjected to heavy pruning in 1987. The next year pruned trees with many vigorous shoots were treated with Paclobutrazol (foliar and soil applications at 0.36% a.i.) or submitted to summer pruning by thinning of the shoots inside the canopy. The treatments were repeated in 1989 and 1990, but only half of the trees were treated in 1990 in order to determine the residual effect of Paclobutrazol.

In 1988, 1989, and 1990 data were collected on: photosynthesis, carbohydrate, starch and chlorophyll content by monthly recording from July to October. Shoot lenght, vegetative and flower buds and staminate ament number were recorded per shoot at the end of each year. Foliar and soil application of Paclobutrazol reduced vegetative activity and promoted flower bud induction. Similar effects were obtained by summer pruning by shoot thinning. The leaves of treated trees were richer in chlorophyll and carbohydrates resulting in more active photosynthesis.

The treatments of Paclobutrazol repeated in 1989 and 1990 confirmed the results of 1988. In 1990 Paclobutrazol showed a residual effect only on trees submitted to foliar application. The effect of Paclobutrazol on growth is similar to thinning of shoots but the mechanism of action is different. Summer pruning reduces shoot lenght by reduction of availability of metabolites, instead, Paclobutrazol does not change leaf number, but modifies the hormonal balance. The residual effect of Paclobutrazol lasts about 1 year after foliage applications.