Apple Fruit Set Research Articles

Gibberellins A4+7 Influence Fruit Set, Fruit Quality, and Return Bloom of Apples

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.

The effects of temperature, vapour pressure deficit and soil moisture stress on growth, flowering and fruit set of custard apple ( Annona cherimola × Annona squamosa) ‘African Pride’

The effects of temperature, vapour pressure deficit (VPD) and soil moisture stress on growth, flowering and fruit set of custard apple (Annona cherimola × Annona squamosa) cultivar ‘African Pride’ were evaluated under controlled-environment conditions. Flowering and fruit set were affected not only by the environmental conditions during flowering, but also by vegetative flushing of the tree. Flowering was closely associated with vegetative flushing. The level of natural fruit set under controlled-environment conditions, irrespective of temperature or humidity, was low (<3.1%) compared to field or container-grown trees flowering under ambient conditions (11 and 28%, respectively). The increased set under ambient conditions appears to be due to the presence of insect pollinators, in particular Nitidulid beetles which were observed in the flowers. High VPD (1.2 kPa) severely reduced both flowering and fruit set. Soil moisture stress (mid-day leaf water potential −2.0 MPa) also reduced flowering and fruit set, particularly at high temperature (28°C). Hand-pollination of flowers, even under high VPD conditions, resulted in a significantly higher set (>20%). Productivity of custard apple in the field may be improved by cultural techniques such as overhead misting, windbreaks and efficient irrigation scheduling.

The effect of four early spring temperature regimes on apple fruit set, tree growth and the K and Ca level in fruits

In 2 experiments, 3-year-old ‘Cox's Orange Pippin’ apple trees, still in rest, were exposed until shortly before bloom to 4 temperature treatments giving 4 patterns of bud development, i.e. rapid or slow throughout, initially rapid followed by slow, and the reverse (first slow, then rapid). During and after bloom, until harvest, all trees were kept at the same temperature. The dates of full bloom differed between treatments by as much as 14 days, but there was little variation in the number of degree-days above 5°C until full bloom. Fruit set was distinctly better when buds developed rapidly than at “slow throughout”, the other treatments occupying an intermediate position. The treatments had little or no effect on shoot growth and fruit size. The amounts of Ca per fruit increased slightly when bud development was rapid initially or throughout the pre-bloom period. For K, the data of the 2 experiments were not consistent.

Influence of Honey Bee (Hymenoptera: Apidae) In-hive Pollen Transfer on Cross-pollination and Fruit Set in Apple

The ability of honey bees, Apis mellifera L., to transfer pollen within the hive through contact with nestmates was tested. In almost all cases, bees acquired pollen from nestmate contacts. Pollen viability was tested by pollinating self-incompatible apple blossoms with treated bees. The contribution of in-hive pollen transfer to cross-pollination and fruit set in apple is discussed.

The Influence of Honey Bee “Sideworking” Behavior on Cross-pollination and Fruit Set in Apples

Abstract Poor fruit set in ‘Delicious’ apple has been associated with blossom morphology, which permits honey bees to obtain nectar while standing on the petals (side-working). We observed honey bees foraging on ‘Delicious’ and recorded the percentage that touched the stigmata. In addition, the percentage of cross-pollinated ‘Delicious’ stigmata was determined daily. The percentage of foragers sideworking ‘Delicious’ initially was low, but increased daily. By the time sideworking became the predominant foraging method, after peak bloom, most blossoms had been cross-pollinated. Initial fruit set on cultivars that can be sideworked was greater than or equal to that on ‘Mcintosh’. These data indicate that cross-pollination and fruit set are not limited significantly because of sideworking.

Fruit-set after pretreatment with foreign compared with killed compatible pollen

A mechanism based on pollen growth-promoting substances has previously been proposed to explain the effects of mentor (killed compatible) pollen when it improves fertility of crosses between nearly incompatible parents. Similarly, pioneer pollination (two pollinations a day apart) stimulates growth of the last applied pollen and increases fruit-set. In the present experiments the effects of foreign-pollen pioneer treatments on fruit-set of apple, sweet cherry, and apricot were compared with the control, killed compatible pollen. All treatments were followed 24 h later with viable compatible pollen. The foreign pollen, Balsamorrhiza sagittata, did not inhibit fruit-set. When the foreign pollen was heat killed, fruit-set was at least as high as when untreated B. sagittata was used. Two other foreign pollens, Taraxacum officinale and Juniperus communis, resulted in lower fruit-set than B. sagittata but still more than the control. This effect was consistent with a previously hypothesized relationship for mentor pollen, relating size and degree of stimulation. The two nonpollen treatments examined, dried yeast and pectinase solution, slightly inhibited fruit-set. Mineral analysis of a composite of pollen and anther tissue indicated that boron and calcium were not deficient in the control pollen, and incompatibility mechanisms and heat-labile metabolites also were unlikely to have been the cause. No direct evidence was obtained, but pollen growth promotion by a diffusible growth regulator (such as gibberellin) is suggested as plausible and an area worthy of further study.

Effect of Fungicidal Sprays During Bloom on Apple Fruit Set and Occurrence of Russet

Effect of Fungicidal Sprays During Bloom on Apple Fruit Set and Occurrence of Russet

Changes in fruit set, leaf size and shoot growth of apple caused by some fungicides, insecticides and a plant growth regulator

SummaryOf seven chemicals sprayed onto apple flowers before flowering or at petal-fall stage one fungicide (triadimefon) increased fruit set, and one insecticide (chlorpyriphos) and the growth regulator (paclobutrazol) decreased it. These three chemicals sprayed at green-cluster stage also reduced eventual leaf size. Later sprays of chlorphyriphos and paclobutrazol sometimes reduced, and gamma-HCH sometimes increased, bourse shoot growth.

Effects of Inhibitors of Ethylene Synthesis or Action, GA4+7, and BA on Fruit Set of Apple, Sour Cherry, and Plum

Abstract Several inhibitors of ethylene synthesis or action were tested to determine their effects on fruit set of apple (Malus domestica Borkh.)9 sour cherry (Prunus cerasus L.) and plum (P. domestica L). None increased set of cherry or plum and only aminoethoxyvinylglycine (AVG) increased set of apple. This compound reduced set in cherry. GA4+7, benzylamino purine (BA), and Promalin (GA4+7 + BA) were ineffective in increasing fruit set of apple with or without AVG, and GA4+7 was likewise ineffective on cherry. AVG (50 to 200 ppm) increased set of apple by as much as 10-fold when applied between pink and petal fall.

Effect of Chemical Thinners on Fruit Set and Fruit Characteristics of AVG-treated Apples

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.

The effect of supplementary hand pollination on fruit set and pollen tube growth in apple

The effect of supplementary hand pollination on fruit set and pollen tube growth in apple

ON THE ROLE OF ETHYLENE IN APPLE FRUIT SET

ON THE ROLE OF ETHYLENE IN APPLE FRUIT SET

The Effect of BeelureR, A Bee Attractant, on the Behavior of Honey Bees and Fruit Set of Apple, 1980

Abstract The effects of Beelure (Helena Chemical Co.) on (1) the number of foraging bees, (2) the percent of bees with pollen, (3) the percent of bees foraging on non-floral foliage and, (4) the fruit set of the trees.were measured. All test were done at the Virginia Polytechnic Institute and State University Horticulture Research Farm in Blacksburg, Virginia.

Pollination, initial fruit set and fruit drop in apples: analysis using mathematical models

SummaryThe pollination model takes account of the effective pollination period (EPP) of the flowers, ovule fertility, insect visiting rate and the probability that insects will be carrying compatible pollen. In the fruit drop model it is assumed that the probability that a fruitlet will drop increases as the number of fertilized ovules it contains decreases; there is also a term for stress. The results indicate that the best strategy for ensuring adequate pollination is that which leads to a high insect visiting rate (e.g. many hives in orchards). Increasing the probability that insects will be carrying compatible pollen also increases the likelihood of successful pollination, but this is a ‘limiting returns’ relationship. Variations in the EPP cause relatively small differences in pollination and fruit set. The models can be used to explore a number of facets of pollination and fruit drop in apples.

Retention of Fruit Firmness and Increase in Vegetative Growth and Fruit Set of Apples with Aminoethoxyvinylglycine1

Abstract Aminoethoxyvinylglycine (AVG), an inhibitor of ethylene synthesis, applied to ‘Delicious’ apple trees (Malus domestica Borkh.) 2 weeks before harvest reduces loss of flesh firmness of apples in storage and increases vegetative growth in the following growth season. When applied to ‘Delicious’ or ‘Golden Delicious’ trees after full bloom, the “June drop” was completely eliminated; thus, fruit set was significantly increased.

Fruit set and June drop in Cox's Orange Pippin apple as affected by pollination and treatment with a mixture of gibberellins A 4 and A 7

Single spray applications of 100 ppm of a mixture of the gibberellins A 4 and A 7 (GA 4 + 7) were made on fruiting spurs of the apple cultivar Cox's Orange Pippin to investigate the effect on set, June drop and growth of fruits, as well as on shoot development and flower-bud formation on the bourses. Applications were made from 1 to 50 days after full bloom following partial hand-pollination of flowers, i.e. two stigmas per flower pollinated. In another experiment applications were made from 1 to 20 days after full bloom following complete (five stigmas per flower) or partial (two stigmas per flower) hand-pollination, after open pollination, or on emasculated flowers. GA 4 + 7 only temporarily increased fruit set after open pollination or after effemination of flowers, and then only after application 1 day after full bloom. GA 4 + 7 did not affect the very high fruit set after complete or partial hand-pollination. Both latter pollination treatments induced an equally high fruit set. GA 4 + 7 reduced June drop significantly whenever fruits were left after first drop, except after early applications following open pollination. GA 4 + 7 was effective in June-drop reduction up to 40 days after full bloom, i.e. until the onset of the June drop. Fruit size was not clearly affected by GA 4 + 7. The smaller fruits obtained in some cases after GA treatment could be explained by assuming that maturity was reached by fruits that would have abscised without an exogenous GA 4 + 7 supply. GA 4 + 7 also increased seed abortion. Fruit length was increased by GA 4 + 7 only for applications made up to 20 days after full bloom. GA 4 + 7 stimulated bourse-shoot development to some extent. Flower-bud formation on the bourses was not clearly affected by GA 4 + 7, but was markedly influenced by the presence of fruits. That GA 4 + 7 reduced June drop so much in spite of a slight promotive effect on bourse-shoot growth and a slight abortive action on seeds suggests that these gibberellins may be specific stimuli for apple-fruit growth after actual fruit set is achieved.

The Utilization of Post-harvest Urea Sprays by Senescing Apple Leaves1

Abstract Senescing apple leaves absorbed 80% of applied urea in 48 hr with greater absorption in light than in darkness. The amount of urea absorbed paralleled the increase in the concn of soluble N and urea N. The bulk of the increase in soluble N was urea and the changes in total soluble N paralleled the changes in urea N. During leaf senescence, chlorophyll, total N and protein declined and much of this N was translocated into storage tissues. Trees which received a post-harvest urea spray produced a significantly greater amount of shoot growth and fruit set of apples than trees receiving no urea or a soil application of urea. The yield was not significantly different between trees receiving a 5% urea spray and trees receiving the soil application of urea. However, the efficiency of N utilization by a 5% urea spray was 4-fold greater than the soil application.

Some Effects of CCC and Alar on Fruit Set and Fruit Quality of Apple1

Abstract The growth retardants, CCC and Alar, were compared for their effects on fruit set and fruit quality of apple. Early season sprays were applied to ‘Golden Delicious’ and midsummer applications were made on ‘Idared’. Pre-bloom sprays of Alar increased fruit set on ‘Golden Delicious’. Pre-bloom applications of CCC and post-bloom applications of Alar tended to reduce set. Neither chemical influenced fruit size, flesh firmness or percent soluble solids of ‘Golden Delicious’ at the concentration used in this study. Pre-bloom sprays of both retardants increased the severity of fruit russet on this cultivar; post-bloom sprays did not affect russet. On ‘Idared’, Alar reduced fruit size and increased red color; it also increased flesh firmness at harvest but not after storage to March. CCC did not affect any measured characteristic of ‘Idared’ apples.

Some Effects of CCC and Alar on Fruit Set and Fruit Quality of Apple1

Abstract The growth retardants, CCC and Alar, were compared for their effects on fruit set and fruit quality of apple. Early season sprays were applied to ‘Golden Delicious’ and midsummer applications were made on ‘Idared’. Pre-bloom sprays of Alar increased fruit set on ‘Golden Delicious’. Pre-bloom applications of CCC and post-bloom applications of Alar tended to reduce set. Neither chemical influenced fruit size, flesh firmness or percent soluble solids of ‘Golden Delicious’ at the concentration used in this study. Pre-bloom sprays of both retardants increased the severity of fruit russet on this cultivar; post-bloom sprays did not affect russet. On ‘Idared’, Alar reduced fruit size and increased red color; it also increased flesh firmness at harvest but not after storage to March. CCC did not affect any measured characteristic of ‘Idared’ apples.

Effects of growth regulators on fruit set and June drop of pears and apples.

To increase yields of pear and apple trees the growth regulators kinetin, gibberellin (A3 and a mixture of A4 and A7), Alar and CCC were applied by spraying on blossoms or fruitlets and by injection into the trunk. Kinetin and particularly gibberellins were effective in stimulating fruit set in pears. Doyenne du Cornice pear set more fruits with a mixture of gibberellin A4 and A7 than with gibberellin A3. Although the majority of stimulated fruits abscised during the June drop period, the crop was markedly increased. The growth retard-ants Alar and CCC were inactive in increasing fruit set, but prevented excessive drop of fruits when applied after a gibberellin application.-Lab. TuinbPl, Wageningen. (Abstract retrieved from CAB Abstracts by CABI’s permission)