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The discovery of auxins provided the basis for current chemical fruit thinning of apples. The promotion of postbloom fruit abscission was first reported over 60 years ago ( Davidson et al., 1945 ), and since then, synthetic auxins, NAA and its

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-naphthaleneacetic acid (NAA) has been successfully used to control basal sprouts in several crops ( Boswell and McCarty, 1974 ; Eynard et al., 1986 ; Holt and Chism, 1988 ; Stover et al., 2006 ) and has shown some success in sucker control in hazelnut in Europe

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synthetic auxins reduced preharvest fruit drop of apples ( Gardner et al., 1940 ; Marini et al., 1993 ) and oranges ( Gardner et al., 1950 ; Zur and Goren, 1977 ). One application of naphthalene acidic acid (NAA) may delay apple fruit drop for ≈10 to 14 d

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, color, and cro p value by as much as 20% while maintaining fruit quality ( Byers and Eno, 2002 ). Naphthaleneacetic acid (NAA), a synthetic auxin, and aminoethoxyvinylglycine (AVG), an inhibitor of ethylene biosynthesis are two compounds that

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Abstract

Leaves of ‘Mountain Snow’ chrysanthemums (Chrysanthemum morifolium Ramat.), sprayed with 10 mm NAA or 10 mm NAAEE, exhibited severe epinasty after 24 hr, while leaves sprayed with 5 mm ethephon did not. Treatment with 100 μm AOA 24 hr before application reduced ethylene production rate of leaves, but not epinasty. Localized application of NAA to adaxial, abaxial, or both leaf surfaces resulted in similar amounts of leaf epinasty. Epinastic leaves had enlarged adaxial epidermal cells. Size of abaxial epidermal cells was unchanged. This study provides evidence that leaf epinasty of chrysanthemum following NAA application is not the result of auxin-induced ethylene production. Chemical names used: (aminooxy)acetic acid (AOA); 1-naphthaleneacetic acid (NAA); 1-naphthaleneacetic acid ethyl ester (NAAEE); and (2-chloroethyl)phosphonic acid (ethephon).

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(NAA) combined with 6-benzylaminopurine (BAP) ( Tokuhara and Mii, 1993 ), thidiazuron (TDZ) ( Ernst, 1994 ), and zeatin ( Park et al., 2003 ). Most of the studies performed to date involve the production of shoots through the formation of protocorm

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tips of strawberry cv. Camarosa was investigated. Two types of auxins, IBA and naphthaleneacetic acid (NAA), in different concentrations, were assessed for root induction. ‘Camarosa’ strawberry is a cultivar that is popularly grown in Cameron Highlands

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NAA at 0.25% to 1.0% applied in late May on the basal portion of thornless blackberry (Rubus, subgenus Eubatus) primocanes inhibited lateral shoot growth in the treated area and reduced the number of primocanes. However, regrowth occurred near or below ground from axillary buds not contacted by NAA. Rates of (0.25% and 0.12570 NAA did not affect the terminal or lateral growth above the treated area. The reduced number of basal lateral shoots facilitated machine harvesting. Chemical name used: napthaleneacetic acid (NAA).

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Experiments were carried out in the southeastern United States between 1998 and 2006 to evaluate the potential for applications of NAA, Ethrel, or both, in the on-year of a biennial bearing cycle to increase return bloom in apple. Four bi-weekly applications of 5 ppm NAA beginning in mid June (summer NAA) increased return bloom, measured as the percentage of floral spurs in the year after treatment. The level of return bloom on trees receiving a summer NAA program was more than 2-fold higher than on untreated control trees, averaged across seven different experiments. Four applications of 5 ppm NAA at weekly intervals leading up to harvest (August/September) increased return bloom also. Combining 150 ppm Ethrel with summer NAA sprays resulted in an additive effect on return bloom compared to NAA or Ethrel alone. The effect of flower cluster density on return bloom the following year was more negative on control trees than it was on trees sprayed with Ethrel in the previous year. Treatment effects on fruit maturity at harvest were generally neutral, although flesh firmness was reduced in some experiments. NAA or Ethrel sprays in the on-year of a biennial bearing cycle may provide a strategy for achieving more consistent flowering and cropping in apple.

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Foliar application of plant growth regulators (PGR) is an established horticultural practice. We are using a finite dose system to examine diffusion of 14C-labeled PGRs, primarily napththaleneacetic acid (NAA), from aqueous droplets and deposits through enzymatically isolated plant cuticles (CM) as affected by spray adjuvant chemistry, solution pH, and epicuticular wax. Recent studies have focused on a nonbuffered aqueous medium, which approximates field application conditions. Despite the negligible buffering capacity of the spray solution, there were significant differences in NAA diffusion with solution pH. At pH 3.2, NAA (pKa = 4.2) diffusion was two-fold greater than at pH 5.2. Additives (surfactants, urea, and urea:NH4NO3, 1:1 mixture) in the spray solutions increased the initial rate and absolute amount of NAA diffused. The polyethoxalated octylphenol surfactant (Triton-X) TX-45 (EO 5.5) enhanced rate and quantity of NAA diffusion. This enhancement was observed with CM, but not after removal of the epicuticular waxes, implicating an interaction between surfactant and waxes. Urea, over a four-fold concentration range, increased NAA diffusion 5% to 31% after 144 h. The urea:NH4NO3 mixture increased NAA diffusion to a greater extent at pH 5.2 (+136%) than at pH 3.2 (+8.4%) after 144 h.

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