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  • Author or Editor: Duane W. Greene x
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Preharvest application of 500 ppm aminoethoxyvinylglycine (AVG) delayed bloom and increased initial fruit set of mature ‘McIntosh’, ‘Spartan’, and ‘Spencer’ apple trees (Malus domestica Borkh.). Final fruit set was enhanced for ‘Spencer’ by a slight suppression of ethylene evolution by flowers harvested during anthesis. AVG reduced fruit weight but increased the fruit length/diameter (L/D) ratios for all 3 cultivars. Vegetative growth effects were confined to an enhancement of spur elongation. Fruit set was improved on ‘Richared Delicious’ and ‘Red Spur Delicious’ by fall (preharvest) and by full-bloom AVG sprays. Postbloom sprays were ineffective. AVG reduced fruit weight but enhanced fruit L/D ratios. A fall treatment of 500 ppm AVG increased both the number and average length of spur shoots on ‘Richared Delicious’. Young ‘Red Spur Delicious’ trees responded to bloom-time AVG (250, 500 ppm) and 6-benzylamino purine (BA) plus gibberellic acid (GA4+7) sprays (500 ppm each) with markedly increased feathering and an overall increase in extension growth and number of leaves per lateral growing point. However, these same treatments reduced the size and weight of individual leaves.

Open Access
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Initial fruit set was increased on ‘Delicious’ and to a lesser extent on ‘McIntosh’ following a 500 ppm preharvest aminoethoxyvinylglycine (AVG) treatment. Final fruit set was increased by AVG only on ‘Delicious’. One day following a chemical thinner application, ethylene production in check and AVG-treated limbs was similar. AVG did not inhibit naphthaleneacetic acid (NAA) induced ethylene production from either fruits or leaves. June drop from AVG-treated limbs appeared to be increased. Carbaryl reduced fruit set on AVG-treated limbs to the same level as on check limbs, while NAA at 15 ppm on ‘Delicious’ reduced the crop load below that of check limbs. AVG reduced fruit size on ‘Delicious’ (which was not overcome by thinners) but did not reduce fruit size on ‘McIntosh’. The length/diameter (L/D) ratios of ‘McIntosh’ and ‘Delicious’ were increased by AVG, but NAA reduced the L/D ratios on both check and AVG-treated limbs. NAA increased the number of “pygmy” fruit on ‘Delicious’, and when combined with preharvest AVG, the number was twice as great as when NAA was applied alone.

Open Access
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`Gardiner Delicious'/MM.lO6 apple (Malus domestics Borkh.) trees were initially sprayed in 1985 with paclobutrazol (PB) at 250 mg.liter-1 at tight cluster and again on 10 and 25 June and 29 July. From 1986 through 1988, PB sprays of 85 or 100 mg·liter-1 were applied at either petal fall (PF) + 2 or PF + 4 weeks and one to two additional sprays were applied per year when growth resumed. Promalin was applied to one group of trees that received PB starting at PF + 2 weeks. PB reduced terminal, lateral, and total shoot growth the year of application and in subsequent years. Although average shoot length of lateral and terminal shoots was reduced, the greatest reduction in growth occurred because PB prevented spurs from growing into lateral and terminal shoots. Compared to unsprayed trees, PB reduced pruning time in all 4 years by 23% to 70%. PB increased bloom only the first year after application, but increased fruit set for 2 years due to a carryover effect. Application of PB in 1985 caused a reduction in fruit size, sometimes in soluble solids concentration, length: diameter (L : D) ratio, and pedicel length. Promalin either overcame the reduction in the ratio or increased it in 1986. Reduced rates of PB in subsequent years caused few adverse effects on the fruit. PB increased flesh firmness when applied at PF + 2 weeks but not at PF + 4 weeks. Trees treated with PB produced fruit with higher flesh Ca and less bitter pit, cork spot, and senescent breakdown following regular air storage. Chemical names used: ß -(4 -chlorophenyl)methyl α -(1,1-dimethylethyl) -1H-l,2,4-triazole-1-ethanol (paclobutrazol, PB); gibberellins A4+7 plus N-(phenylmethyl) -1H-purine-6-amine (Promalin).

Free access
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Several experiments were conducted to evaluate the influence of time, concentration, and number of GA4+7 applications on ‘McIntosh’, ‘Early McIntosh’, and ‘Empire’ apples (Malus domestica Borkh.). GA4+7 at 150 mg·liter−1 increased fruit set and inhibited flower bud formation on ‘McIntosh’ and ‘Early McIntosh’. Flower bud formation was inhibited on ‘McIntosh’ when GA4+7 was applied over a wide range of times from 6 days before full bloom to 34 to 35 days after full bloom. Applications made 45 and 60 days after full bloom had no effect. Following storage, ‘Empire’ fruit treated with GA4+7 were softer and had a higher incidence of senescent breakdown than controls. Postbloom sprays of GA4+7 increased fruit set on ‘Empire’ one year when applied from 0 to 150 mg·liter−1, while two applications of 50 mg·liter−1 on similar trees in another year caused thinning. GA4+7 sprays appeared to advance ripening of ‘Empire’ apples. Gibberellin sprays reduced seed number. GA4+7 inhibited flowering in ‘Empire’. Repeat applications 19 and 34 days after full bloom were only slightly more inhibitory to flowering than one application of 0, 50, 100, or 150 mg·liter−1 made 10 days after full bloom.

Open Access
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Abstract

A postbloom foliar application of 1500 and 3000 ppm paclobutrazol (PB) increased flesh firmness of ‘Delicious’ apple (Malus domestica Borkh.) but reduced seed number and fruit size at harvest. The following year, flowering was not affected, but fruit set was increased. A decrease in terminal growth, leaf size, fruit L/D ratio, fruit size, pedicel length, and fruit soluble solids were also observed with the high rate of PB. PB increased fruit flesh calcium and total yield, and retarded fruit ripening. Dichlorobutrazol (DCB) did not affect final terminal growth but reduced L/D ratio, pedicel length, and fruit size the year after application. Following storage, flesh firmness of PBtreated fruit was not influenced, but senescent breakdown was dramatically reduced. Retarded ripening and reduced senescent breakdown were attributed to increased calcium in fruit flesh. Variability in terminal growth was increased as the inhibitory effects of PB dissipated. Three years after application, fruit L/D ratio and pedicel length were decreased, even though there was no longer a reduction in terminal growth. Chemical names used: (2RS, 3RS)-1-(2,2-dichlorophenyl-4-4-dimethyl-2-(1H,1,2,4-triazol-lyl)pentan-3-ol (paclobutrazol); (2 RS, 3 RS)-1-2,2-dichlorophenyl-4,4-dimethyl-2-(1H1,2,4-triazol-lyl)pentan-3-ol (dichlorobutrazol).

Open Access
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Abstract

Sprays of silver nitrate (AgNO3), aminoethoxyvinylglycine (AVG) and gibberellins A4+7 (GA4+7) plus 6-benzylamino purine (BA) were applied with 0.1% Triton B-1956 at bloom to ‘Richared Delicious’ apple trees (Malus domestica Borkh.). AVG at 200 ppm alone or when applied with 50 ppm each of GA4+7 and BA increased fruit set whereas GA4+7 plus BA applied alone at 50 ppm caused fruit thinning. AVG reduced endogenous ethylene production and overcame the increased ethylene production brought about by GA4+7 plus BA application. AVG applied alone at 200 ppm or when combined with GA4+7 plus BA reduced fruit size and increased the L/D ratio at harvest.

Open Access
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Regulation of biennial bearing in pome fruit is usually accomplished by chemically removing fruit during the “on” cycle. The advantages and disadvantages of regulating biennial bearing by inhibiting flowering in the “off” cycle were discussed. Gibberellins and the two phenyl urea cytokinin-like compounds, thidiazuron and CPPU have been shown to inhibit flowering in pome fruit. It was concluded that inhibition of flowering with commercially available gibberellins was not a commercially acceptable approach to regulate biennial bearing. The inhibition of flowering was erratic, fruit thinning and increased fruit set could not be predicted, and seed abortion following gibberellin application could predispose fruit to reduced postharvest life because of reduced calcium uptake. Regulation of flowering by inhibiting flower bud formation appeared to be a viable way to regulate cropping on nonbearing tress or trees that were not carrying a crop.

Full access
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Plant growth regulators (PGRs) play an important commercial role in horticulture. Although often expensive, they are generally used on high value crops where the costs can be retrieved through the increased value their usage creates in a given crop. The impetus for development of new PGRs is generally initiated by the agrochemical industry where they perceive a need that has a profit potential, whereas the motivation for the development of a PGR by researchers is largely to aid the industry they serve. University and government researchers initially follow a prescribed protocol early in the development process, but once they have gained personal experience with a PGR, further research is often guided by personal observations and keen technical insight. During the development and evaluation process, university and government researchers are optimistic, and negative effects are generally viewed as challenges, that can and will be overcome. Discussion and effective communication are critical components in the overall development of a new PGR. Researchers generally exchange information very freely, unless restricted from doing so by a nondisclosure or other contract agreement. The underlying goal for university and government researchers is to get approval of a new PGR product and/or use that will allow growers to produce a high quality product for consumers with an improved profit margin for growers. Development of new PGRs is undergoing major change that unfortunately will lead to the development and registration of fewer compounds. There are not as many agrochemical companies, there are a decreasing number of university and government researchers, and diminishing funds available to support the development of new PGRs.

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