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Jose P. Morales-Payan and Bielinski M. Santos

Container experiments were conducted in the Dominican Republic to determine the effects of gibberellic acid (GA3) and nitrogen (N) treatments on the seedling growth of Spanish lime (Melicoccus bijugatus), golden apple (Spondias dulcis), and acerola (Malpighia punicifolia). The three species responded with linearly increased height and dry weight to increasing GA3 levels. Each species responded differently to N rates. Spanish lime did not respond to N supply, whereas golden apple was highly responsive and the growth of acerola was reduced at high N rates.

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Bielinski M. Santos and Jose P. Morales-Payan

Nursery experiments were conducted in the Dominican Republic to determine the tolerance of tamarind (Tamarindus indica), acerola or Barbados cherry (Malpighia punicifolia), and zapote (Calocarpum sapota) irrigation with saline water (0, 2, 4, 6, and 8 dS/m) at different frequencies (every 24, 48, and 72 hours) during 60 days. Results indicate that tamarind was the less salt-sensitive and zapote the less salt-tolerant of the three species. Linear relationships were found between salt concentration and growth, with biomass accumulation decreasing as salinity and irrigation frequency increased.

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Bielinski M. Santos and Jose P. Morales-Payan

The response of young `Cartagena Ombligua' papaya (Carica papaya) plants to soil-applied copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn) was determined. Nursery experiments were conducted in the Dominican Republic, where Cu (0, 0.023, 0.046, 0.069, and 0.092 g), Mn (0, 0.27, 0.54, 0.81, and 1.08 g), Fe (0, 0.49, 0.98, 1.47, and 1.96 g) and Zn (0, 0.2, 0.4, 0.6, and 0.8 g per plant) were individually applied 20 days after transplanting. There were significant responses to the four elements. Maximum growth was obtained with 0.092 g Cu, 0.4 g Zn, 0.54 g Mn, or 0.98 g Fe per plant.

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Bielinski M. Santos and Jose P. Morales-Payan

Studies were conducted in the Dominican Republic to determine the short-term response of young `Cartagena Ombligua' papaya (Carica papaya) plants to nitrogen (N), phosphorus (P), and potassium (K) fertilization. N, P2O5, K2O were individually applied 20 days after transplanting at rates 0, 6, 12, 18, and 24 g per plant. Plant height, stem diameter, leaf area, and root and shoot dry weight responded to N and K in a quadratic fashion (N:Y= 30.79+ 1.35X-0.07X2; K20:Y = 30.02 +1.6X - 0.06X2). Maximum growth was obtained with 6 and 18 g of N and K2O, respectively. P fertilization did not significantly affect shoot growth, but it stimulated root growth (Y = 2.02 + 0.41X - 0.013X2).

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Bielinski M. Santos and Jose P. Morales-Payan

The effect of varying calcium (Ca), magnesium (Mg), boron (B), and molybdenum (Mo) rates on the growth of young `Cartagena Ombligua' papaya (Carica papaya) plants was studied in experiments conducted in the Dominican Republic. Rates of 0, 3, 6, 9, and 12 g Ca; 0, 0.85, 1.7, 2.55, and 3.4 g Mg; 0, 20, 40, 60, and 80 mg B; and 0, 0.05 0.1,0.15 and 0.2 mg Mo per plant were applied to the soil 20 days after transplanting. Ca did not stimulate plant growth, but instead was toxic at rates of 9-12 g per plant. Mg fertilization significantly stimulated root growth (Y = 2.35 + 0.48X, r 2 = 0.95), but not shoot growth. Mo applications decreased plant growth, whereas B enhanced overall plant growth (Y = 10.64 + 70.5X, r 2 = 0.96).

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Jose P. Morales-Payan and Bielinski M. Santos

Experiments were conducted in the Dominican Republic to determine the effect of physical and chemical treatments on the germination of the ornamental palms Roystonea hispaniolana Bailey (Royal palm), Acrocomia quisqueyana Bailey (Corozo palm), Sabal umbraculifera Mart (Cana palm), Phoenix canariensis (Canary Islands date palm), Veitchia merrillii (Becc) Bailey (Manila palm), Chrysalidocarpus lutescens Wendl (Areca palm), and Caryota urens (Fishtail palm). Treatments were seed immersion in water or gibberellic acid 3 (GA3) solution for 72 hours, immersion in concentrated nitric acid for 5 minutes, or cracking of the seed coat. Rate and percentage of emergence 90 days after treatment were measured. The best results for Roystonea, Phoenix, Veitchia, Caryota, and Chrysalidocarpus were obtained soaking the seeds in water or a 200-ppm gibberellic acid solution. Nitric acid and seed coat cracking significantly reduced the germination percentage in all the species, except Acrocomia guisqueyana and Sabal umbraculifera. Seeds of Acrocomia did not germinate as a response to any of the treatments tested. Sabal seeds germinated only after coat cracking or nitric acid treatment.

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Bielinski M. Santos and Jose P. Morales-Payan

Trials were conducted under controlled conditions to determine the tolerance of young papaya plants (15 cm tall) to postemergence herbicides. Herbicides used were paraquat (1.68 Kg ai/Ha), MSMA (2.24 Kg ai/Ha), 2,4-D (4.26 Kg ai/Ha), bromoxynil (0.28 Kg ai/Ha), cyanazine (1.12 Kg ai/Ha), dimethenamid (1.12 Kg ai/Ha), endothal (0.56 Kg ai/Ha), imazameth (0.067 Kg ai/Ha), imazethapyr (0.028 Kg ai/Ha) lactofen (0.12 Kg ai/Ha), oxyfluorfen (0.03 Kg ai/Ha), acifluorfen (0.28 Kg ai/Ha), atrazine (2.24 Kg ai/Ha), and bentazon (1.12 Kg ai/Ha) as well as the untreated control. Atrazine, bentazon, cyanazine, imazemeth, imazethapyr, and dimethenamid did not cause phytotoxicity at the rates used and were equal to the untreated control. Other herbicides caused severe injuries followed by total death at 10 days after treatment.

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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.

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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, 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.