ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
EFFECTS OF PACLOBUTRAZOL ON SHOOT GROWTH AND FRUIT THINNING OF PEACH TREES |
| Author: | A. Blanco |
| Abstract:
The control of tree size in deciduous fruit species has been a major concern to reduce production costs. In peach and nectarine (Prunus persica (L.) Batsch), the need for a reduction in tree growth has been recently stated and thus, work on the growth inhibiting effect of different plant growth regulators has started. The results obtained with Paclobutrazol (PP333) in several fruit species (Quinlan, 1981) led us to design several experiments to test the effects of this growth regulator as a shoot growth inhibitor and as a fruit thinning agent in peach and nectarine trees. Six-year-old trees of 'Crimson Gold' nectarine, planted in a plot with sandy to sandy-loam soil, and subjected to flood irrigation, were treated with different amounts of PP333 applied at the beginning of April onto the soil, or as foliar sprays of 1 000 ppm and 250 ppm, this last one applied twice: in April and in July, after the harvest had been completed. A significant inhibition of shoot growth was found in the trees treated on the soil with the higher amounts of PP333 compared with the untreated controls, this difference being detected as early as June. The trees, all hand thinned to the same level, showed no significant differences in yield, in terms of total crop weight and number of fruits, although the mean fruit weight was greater in the trees treated with Paclobutrazol compared to the controls, the difference being significant when PP333 was applied to the soil. Foliar sprays were not as effective as soil applications. To test the effect on fruit drop, two experiments were carried out on 5-year-old 'Redhaven' and 6-year-old 'Sudanell-l' peach trees, in which foliar sprays of 2 000 ppm of Paclobutrazol were applied to the trees in three different dates: petal fall, cot split and at the beginning of pit hardening. These were compared to trees either hand-thinned or left unthinned. Different responses were observed on the two cultivars: periodical counts on the number of fruits showed no effect on their drop in 'Redhaven', following the application of PP333 being the yield only different when trees had been hand thinned and the fruits significantly greater. Shoot growth was inhibited by PP333 mainly on the two later applications, being the internodes shorter in these shoots. In 'Sudanell-l' certain fruit drop was recorded on branches of the trees treated at the earlier dates, reaching at harvest the same level as in the hand thinned trees. The yield per tree was smaller on the trees treated at these earlier dates compared to the other treatments, but only when the application was done at petal fall the fruits were larger. Shoot length was significantly shorter on the trees treated on the later dates, but the effect was smaller than in 'Redhaven'. | |
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