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Abstract
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.
Abstract
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.
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.
`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).
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).
Abstract
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.
Pome fruit display a biennial bearing tendency that is characterized by heavy flowering and fruit set one year followed by a year with reduced bloom and fruit set. This tendancy results in a year with heavy cropping with small fruit, and a subsequent year with large fruit and a small crop. Both situations are undesirable. Chemical thinners in the “on” year are frequently used to modify this cropping behavior. Alternative methods to control cropping by flower bud inhibitions will be discussed. Gibberellin application in the “off” year at or soon after bloom will inhibit flower bud formation and encourage moderate flowering. This method of crop regulation has been used infrequently. Gibberellins differ in their ability to inhibit flowering. Therefore, selection of a specific gibberellin and an effective concentration range may provide greater flexibility in controlling flowering. The cytokinins CPPU and thidiazuron inhibit flower bud formation, increase fruit size, and also thin fruit. Appropriate application of these cytokinins will be discussed where beneficial effects on fruit size may be achieved while maintaining a moderate level of flower bud formation.
The lack of pollination and the effects of blossom thinners were simulated by enclosing selected `McIntosh' apple spurs in super-light insect barrier netting at the pink stage of flower development. Fruit set was recorded and fruit size measured at 2- to 3-day intervals from petal fall until initial set. The effects of lack of pollination or the use of blossom thinners on initial set could not be determined with any degree of accuracy until at least 8 days after petal fall. NAA was applied at 8 ppm when fruit were 8.5 mm in diameter. Fruit set and fruit size were taken at 2- to 3-day intervals until the end of June drop. Fruit set on NAA-treated trees was greater than that on check trees for 2 weeks following application. Although NAA ultimately did cause significant thinning, it was not until 3 to 3.5 weeks after application that it was possible to determine with accuracy the thinning response to NAA. However, the thinning response to NAA could be predicted within a week after application, since growth of fruitlets that ultimately abscised slowed 4 to 7 days after the application of NAA. A working model to predict effective pollination and the response to chemical thinners in apples will be discussed.