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Gonzalo Morales-Salazar, Bielinski M. Santos, and Jose P. Morales-Payan

Field experiments were conducted in the Dominican Republic to determine the effect of gibberellic acid (GA) and nitrogen (N) treatments on the growth of lateral branches in young `Keitt' mango plants. Two-year-old `Keitt' mango plants were pruned and treated with combinations of gibberellic acid (0, 20, 40, 60, 80, and 100 ppm) foliar sprays and soil nitrogen fertilization (18.75, 37.50, and 56.25 g). There were no N by GA interactions. Treatments did not significantly influence days to sprouting, number of sprouts, or number of leaves per sprout. N rates did not affect sprout length, whereas increasing GA rates enhanced sprout elongation. The effect of GA was described by the linear equation Y = 14.59 + 0.27X. Results indicate that GA sprays can be used to enhance sprout elongation to promote the desired round shape in canopies of `Keitt' mango plants.

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Jose P. Morales-Payan, Gonzalo Morales-Salazar, and Bielinski M. Santos

Field and container experiments were conducted in the Dominican Republic to determine the effect of gibberellic acid 3 (GA3) rates on papaya ringspot virus (PRSV)-infected seedlings and adult plants of `Cartagena Ombligua' papaya. The apical region of PRSV-infected and PRSV-uninfected plants was sprayed with GA3 aqueous solutions at rates 0, 25, 50, 75, and 100 ppm. PRSV-uninfected adult plants and seedlings produced longer internodes as GA3 rates increased. Adult PRSV-uninfected plants flowered normally at any GA3 rate. PRSV-infected seedlings and adult plants also responded to GA3 sprays, but to a lower extent. Typical symptoms of the disease were present in all the infected plants regardless of the GA3 rate applied, and adult plants did not flower at any rate. Results indicate that PRSV-infected `Cartagena Ombligua' papaya plants are responsive to exogenous GA3, although in a lesser degree than PRSV-uninfected plants. Linear regression equations described the effect of GA3 on the stem elongation of PRSV-infected and uninfected `Cartagena Ombligua' seedlings and adult plants.

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Gonzalo Morales-Salazar, Jose P. Morales-Payan, and Bielinski M. Santos

Field experiments were conducted in the Dominican Republic to determine the effect of gibberellic acid treatments on the elongation of the leading and lateral branches of `Hall' and `Semil-34' avocado (Persea americana) plants. The plant growth regulator was applied as a foliar spray to the leading branch at rates 0, 20, 40, 60, and 80 ppm. `Hall' avocado was not responsive to gibberellic acid treatment, whereas `Semil-34' was responsive, with higher rates inducing a more pronounced stem elongation. As an undesirable side effect, gibberellic acid treatment also stimulated the elongation of lateral branches in `Semil-34', making it unsuitable to enhance apical dominance on the leading branch.

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Gonzalo Morales-Salazar, Jose P. Morales-Payan, and Bielinski M. Santos

The effect of three plant growth retardants, bitertanol, tradimefon, and hexaconazole, on short-term vine regrowth of pruned `Arabe' grape (Vitis vinifera) was studied in field experiments conducted in the Dominican Republic. Individual soil drench treatments of the three retardants were applied to adult pruned `Arabe' grape plants at rates 0, 0.25, 0.50, 0.75 and 1.00 g active ingredient per plant. Three weeks after treatment, bitertanol did not have a significant effect on vegetative growth, whereas triadimefon and hexaconazole caused significant reductions on vine regrowth. The effect of triadimefon as a growth retardant was stronger than that of hexaconazole, as described by regression equations Y = 30.88 - 25.68X for triadimefon, and Y = 32.9 - 15.2X for hexaconazole.