Apple Fruit Set Research Articles

Effects of environment, season and crop load on gas exchange and plant water status of Annona spp. hybrid cultivar, African Pride

SummaryDiurnal changes in net carbon dioxide assimilation (A), leaf conductance (gs) and leaf water potential (ψL) were investigated for custard apple (Annona cherimola × Annona squamosa) trees of cultivar ‘African Pride’ in subtropical Queensland, Australia. Most of the variation in A and gs could be attributed to changes in r.h. (r20.69, P<0.05). The addition of other variables besides r.h. into multiple linear regressions analysis added little to explaining the variation in A or gs. Leaf water potential (ψL) was highly responsive to air temperature (AT) (r2 = 0.56, P<0.05). The marked sensitivity of custard apple stomata to low r.h. may be one of the reasons for poor fruit set and size of custard apple fruit under subtropical conditions because of carbohydrate source limitations. The fruit set and early fruit growth of custard apple in the field could be improved by techniques which raise r.h., such as the use of windbreaks and overhead intermittent misting.

528 Modeling of Fruit Set in Apple—Approaches, Model Structure, and Initial Results

Several models of apple tree carbon balance have been developed, including a simplified model by our lab. Tree photosynthesis and total dry matter production is the best characterized except for root growth and root respiration. Once dry matter is produced and partitioned to the different organs (another key problem for modeling), the effects of carbon availability to the fruits on their growth and abscission needs to be modeled. Our approach is based on an observed relationship between increased abscission with decreased fruit growth rate of populations of fruit. From several empirical studies of fruit growth and abscission during chemical thinning or imposed stress early in the season, a relationship was found between % abscission and classes of fruit growth rates. It appears to be best if the fruit growth rate is expressed as a percent of the growth rate of the fastest growing group of fruits in each study. Thus in the model the fruit growth allowed by the available carbon each day is compared to a pre-determined maximum growth rate for the cultivar. The percent-of-maximum growth rate then determines how much abscission will occur. Then the growth rate of the remaining fruit is calculated. Additional parameters of the model allowed for a multiple-day buffer of carbon availability, an imposed fruit number reduction (i.e. equivalent to hand thinning), and temperature effects. Although there are more improvements planned, the initial tests have been promising with the simulations showing realistic patterns of fruit abscission and fruit growth.

Commercial-scale Use of Hydrogen Cyanamide for Apple and Peach Blossom Thinning

Hydrogen cyanamide (Dormex, 50% a.i.) for blossom thinning `Early Spur Rome' and `Law Rome' apple (Malus×domestica Borkh.) and `Flavorcrest' peach (Prunus persica L.) was applied with air-blast sprayers on a commercial scale. Full-bloom applications of hydrogen cyanamide at 4 pts formulation per 200 gal/acre (1288 mg·L−1) and 5 pts formulation per 200 gal/acre (1610 mg·L−1) significantly reduced fruit set in apple and peach. In `Early Spur Rome', a postbloom application of carbaryl [Sevin XLR Plus, 4 lb a.i./gal (0.48 kg·L−1)] following a full-bloom spray of hydrogen cyanamide increased fruit thinning with a significant increase in fruit size compared to an application of hydrogen cyanamide alone. In `Law Rome', trees receiving a full-bloom application of hydrogen cyanamide followed by a postbloom application of 1-naphthyl-N-methylcarbamate (carbaryl) + naphthalene acetic acid (NAA) had significantly lower fruit set and larger fruit than those in the carbaryl + NAA treatment. Apples or peaches were not marked by hydrogen cyanamide.

Applications of Endothalic Acid, Pelargonic Acid, and Hydrogen Cyanamide for Blossom Thinning in Apple and Peach

Blossom thinning of `Early Spur Rome' apple (Malus domestica Borkh.) and `Redhaven' peach (Prunus persica L.) with hydrogen cyanamide (Dormex, 50% a.i.), endothalic acid [(Endothal, 0.4 lb a.i./gal (47.93 g a.i./L)], and pelargonic acid (Thinex, 60% a.i.) was studied in 1995 and 1996. Full-bloom applications of hydrogen cyanamide at 2 pt formulation/100 gal (1288 mg a.i./L) and 2.5 pt formulation/100 gal (1610 mg a.i./L) or endothalic acid at 1 pt formulation/100 gal (59.9 mg a.i./L), once at 70% bloom and again at full bloom, reduced apple fruit set. Pelargonic acid was only effective in thinning apple blossoms when applied twice—at 40% bloom and again at full bloom—at 1.5 pt formulation/100 gal (1.12 mL a.i./L) per application. Pelargonic acid marked apples in 1995 but not 1996. Neither hydrogen cyanamide nor endothalic acid marked apples. A single full-bloom application of hydrogen cyanamide, endothalic acid, or pelargonic acid effectively thinned peach blossoms in 1995; however, in 1996, only hydrogen cyanamide at 2.5 pt formulation/100 gal effectively thinned peach blossoms. Peaches did not show fruit marks with any of the peach blossom thinners.

The role of ethylene in apple fruit set

SummaryApplication of branch sprays of silver thiosulphate (STS) and of aminooxyacetic acid (AOA) did not affect fruit set or fruit size in three apple cultivars. In contrast, sprays of aminoethoxyvinyl glycine (AVG) (100 and 200 ppm) improved fruit set of open-pollinated flowers. Ethephon (40 to 100 ppm) did not affect fruit set significantly, yet at 100 ppm it eliminated the promotive effect of AVG. In two experiments, AVG tended to reduce ethylene production from flowers excised 1–10 d after treatment, but variability was high and the differences were not statistically significant. In an additional experiment, AVG inhibited ethylene production by all portions of dissected flowers (pedicels, receptacle, petals), with least effect on peduncles/pedicels. The peduncle/pedicels produced 5 to 25% of the total ethylene evolved by the flower cluster, the receptacle 20 to 50% and the petals approximately 50%.

FUNCTIONALITY OF POLLEN AND FRUIT SET IN APPLES

FUNCTIONALITY OF POLLEN AND FRUIT SET IN APPLES

The Effect of Accel and Carbaryl on the Fruit Set, Yield, Quality, and Leaf Mineral Composition of Apples

Experiments were performed to determine the effect of Accel and carbaryl on the fruit set, yield, quality, and leaf mineral composition of three apples cultivars: `Empire', `Jon-A-Red', and `Braeburn'. The treatments used were Accel at 25, 50, and 75 ppm; carbaryl at 0.05%, 0.1%, and 0.2%. There were significant increases in length: diameter ratio, weight of fruit per tree, pH, and percent red color. Mean fruit weight, percent N, K, and Mg as the rates of Accel and carbaryl increased. Sugar content in the fruit and the levels of P, Ca, Mn, Fe, Cu, and Zn in the leaves were not affected. We conclude that the increased fruit weights were due to increased cell numbers and the few fruit that remained after thinning, thereby leading to increased amounts of assimilates directed to the developing fruit. The increase in percent red color is indicative of the effect of the treatments on the degree of ripening.

The relationship between early-season leaf feeding by apple rust mite,Aculus schlechtendali(Nal.), and fruit set and photosynthesis of apple

SummaryComparisons were made of numbers of fruit set on individual blossom clusters or whole trees of apple cvs Bramley’s Seedling and Cox’s Orange Pippin infested with large numbers of apple rust ...

EFFECT OF ROOTSTOCK ON FLOWERING BEHAVIOUR, FRUIT SET, YIELD AND FRUIT CHARACTERS OF ANNA APPLE

EFFECT OF ROOTSTOCK ON FLOWERING BEHAVIOUR, FRUIT SET, YIELD AND FRUIT CHARACTERS OF ANNA APPLE

Thidiazuron Effects on Fruit Set, Fruit Quality, and Return Bloom of Apples

Thidiazuron (THI) applied at full bloom (FB) at 10 or 50 mg·liter–1 thinned `McIntosh' apples (Malus domestica Borkh.) and reduced return bloom. The same concentrations applied at 22 days after FB (DAFB) thinned excessively and inhibited return bloom even more. THI at 1, 5, or 15 mg·liter–1 did not thin `Empire' at FB, but when applied 18 DAFB, these concentrations achieved thinning, with 5 mg·liter–1 reducing crop load to near ideal commercial levels. Return bloom of `Empire' was not influenced by THI at these concentrations. THI increased fruit weight, flesh firmness, soluble solids concentration, and fruit asymmetry on `McIntosh' and `Empire' and reduced red pigmentation and seed count on `McIntosh', especially when applied 22 DAFB. A FB application of CPPU and THI, each at 5 or 10 mg·liter–1, on `Delicious' increased the fruit length: diameter (L: D) ratio and flesh firmness (at harvest and following 26 weeks of refrigerated storage and reduced return bloom). CPPU at either 5 or 10 mg·liter–1 increased the fruit L: D ratio more than 25 mg Promalin/liter. Chemical names used: N-phenyl-N′-1,2,3-thiadiazol-5-ylurea (thidiazuron); N-(2-chloro-4-pyridyl)-N′-phenylurea (CPPU); N-(phenylmethyl)-1H-purine-6-amine plus gibberellins A4+7 (Promalin).

Validation of PC-REDAPOL: Fruit Set Prediction Model for Apples

The personal computer version of the REDAPOL apple fruit set prediction model has been validated in Arizona and Washington orchards. The PC-REDAPOL computer simulation model is designed to predict the percentage of blossoms setting fruit on apple trees. PC-REDAPOL predictions were within the 95% CI of the actual average percentage of blossoms setting fruit in 16 out of 23 model validation tests. The model also accurately predicted fruit set on limbs where honey bee, Apis mellifera L., visitation and pollination were stopped at different points during bloom. PC-REDAPOL has all the features of the original REDAPOL model, plus additions such as the ability to update estimates of the honey bee foraging population on apple trees during a simulation, pest management information, and a degree-day calculator. The program runs on IBM compatible personal computers and is available on request.

Comparison of NAA and Carbaryl Petal-fall Sprays on Fruit Set of Apples

Biennial bearing of apple trees can be overcome either by the use of a blossom chemical thinner or by early application of a postbloom thinner. Carbaryl (Sevin) is a post-bloom fruit-thinning chemical with an effective thinning period of 4 to 5 weeks after bloom. Sevin was compared in 1992 and 1993 with NAA as an early petal-fall spray. Sevin treatments reduced fruit set to one fruit per cluster with no adverse side effects on the foliage. NAA inconsistently reduced fruit set and the remaining fruit were in clusters, The NAA-treated foliage was adversely affected; having small curled leaves. NAA at 10 ppm under-thinned in 1992 and seriously over-thinned in 1993, whereas Sevin treatments were consistent for fruit thinning in both years. Sevin applied at petal-fall or at petal-fall + 7 days effectively reduced fruit set and reduced fruit competition.

COMPARISON OF NAA AND SEVIN PETAL FALL SPRAYS ON FRUIT SET OF APPLES

In Washington and other western states Elgetol, a blossom thinning agent was previously used before the postbloom NAA and Sevin applications and there was no need for an earlier timing of NAA and Sevin treatments. In 1989, Elgetol was removed from the market by the manufacturer because of minor crop use and the high cost of re-registration. Without a blossom thinner it is impossible to guarantee a return bloom on severe biennial bearing cultivars such as Golden Delicious and Fuji. Even though adequate fruit thinning occurs with the postbloom thinning sprays, flower Initiation may not occur for the next years crop because the application is made too late.NAA and Sevin are used as postbloom sprays for reducing fruit set of apples. The usual time of application is when the largest fruit are from 10 to 15 mm in diameter. Sprays applied at the 10-15 mm fruit diameter stage take advantage of warm weather after spraying which increases stress and maximizes reduction of fruit set with a minimum effect on the seed number, however, when temperature is cold seed abortion occurs without adequate reduction of fruit set.This report compares the efficacy of the postbloom thinners NAA and Sevin as early petal fall sprays for reducing fruit number and increasing return bloom the following year. Sevin is most effective as an apple fruit abscission agent when applied at petal fall. In trials for 2 years there was no reduction in fruit seed number, no reduction in fruit size and no effect on fruit shape. In comparison NAA applied at petal fall tended to reduce seed number, reduce fruit size, flatten or distort fruit shape and cause leaf curling.

Effects of varying pollen load on fruit set, seed set and seedling performance in apple and pear

Two apple crosses and one pear cross were carried out using three different pollen densities. In one of the apple crosses, both fruit and seed set decreased when a mixture of pollen and powder (diluted pollen treatment) was used for pollination. Also, seedlings from the undiluted treatment were more vigorous than those originating from pollination with diluted pollen. In the other apple cross, however, no effect on fruit set, seed set or growth in the first year was found. Mean diameter after the second year differed among treatments, but did not seem to be related to pollen density. For pear, the number of good seeds decreased and the number of deaf, probably unfertilized, seeds increased with decreasing pollen density. However, there was no apparent significant effect of pollen density on seedling growth. With respect to scab resistance and mildew attack in both apple crosses, no differences among treatments were found. The results indicate that gametophytic competition may occur in apple crosses, but that it is probably weaker in pear.

EFFECT OF FOLIAR APPLICATIONS OF FISH HYDROLYSATE FERTILIZER OR UREA ON APPLE YIELD AND FRUIT QUALITY

A study was conducted in 1992 at Highmoor Farm, Monmouth, ME to test the effects of fish hydrolysate fertilizer on fruit set, fruit size and fruit quality of apple. Mature, semi-dwarf `Delicious' and `Golden Delicious' trees received 2.76g/1 N, supplied by either fish hydrolysate fertilizer or urea, or received no fertilizer (control). Fertilizers were applied via three foliar sprays applied at seven day intervals, beginning at petal fall. Fish hydralysate fertilizer reduced fruit set of `Delicious' and `Golden Delicious'. Foliar urea increased fruit set and yield of 'Golden Delicious'. Neither fertilizer affected mineral nutrient concentrations of leaves collected in July. Fish hydrolysate increased fruit russeting on both cultivars. Fish hydrolysate is not recommended as a foliar fertilizer for apples.

CPPU Influences Fruit Quality, Fruit Set, Return Bloom, and Preharvest Drop of Apples

CPPU was applied to whole spur `Delicious' apple (Malus domestica Borkh.) trees in central Washington at 0,6.25,12.5,25, or 50 mg·liter-1 at full bloom (FB) or FB plus 2 weeks. At both application times, the flesh firmness of treated fruit linearly increased with increasing concentration. CPPU applied at 0,5,10,15, or 20 mg·liter-1 to spur `Delicious' trees in Massachusetts at king bloom resulted in a linear increase in flesh firmness at harvest and following 28 weeks in air storage at 0C. CPPU did not affect the incidence of senescent breakdown, decay, or cork spot. Fruit length: diameter (L/D) ratios generally increased at all doses. Fruit weight was not influenced at either location. All CPPU concentrations reduced return bloom on `Delicious' apples in Massachusetts in 1989. Of the 10, 20, or 40 mg·liter-1 treatments for `Empire' apples, only CPPU at 40 mg·liter-1 reduced return bloom. CPPU applied to `Empire' apples in Massachusetts did not effect fruit set, soluble solids concentration, L/D, or firmness; however, fruit weight increased linearly with concentration. CPPU applied at 100 mg·liter-1 retarded preharvest fruit drop of `Early McIntosh' in Massachusetts for ≈7 days but was not as effective as NAA at 20 mg·liter-1. In a larger semicommercial trial, `Delicious' fruit treated with CPPU at 5,10, or 15 mg·liter-1 at FB, petal fall (PF), or PF plus 1 week, respectively, were harvested and graded over a commercial packing line. Malformities caused by CPPU at the highest doses reduced packout, although all CPPU application rates reduced the percent fruit culled due to poor color. CPPU increased packed fruit size, since the size of fruit (64 mm in diameter) in the &gt;150-fruit/box size decreased, while the size of fruit (72 mm in diameter) in the 100- and 130-fruit/box sizes increased. Treated fruit stored for 7 months at 1C were firmer than nontreated controls. Chemical names used: N-(2-chloro-4-pyridyl)- N' -phenylurea (CPPU); 1 naphthalene-acetic acid (NAA).

Use of hydrogen cyanamide for apple and plum thinning

Effects of various concentrations of Dormex (a.i. 49% hydrogen cyanamide) on fruit thinning of ‘Rome Beauty’ apple (Malus domestica Borkh.), ‘Friar’ and ‘Simka’ plums (Prunus salicina Lindley) were studied. A full bloom application of Dormex at all tested concentrations decreased ‘Rome Beauty’ apple fruit set and yield, and increased fruit weight. Dormex at 0.25% (v/v) resulted in adequate apple thinning, indicated by production of an optimum fruit weight (320 g). Prebloom and full bloom applications of Dormex at greater than 0.75% reduced plum fruit set and yield in ‘Friar’. Full bloom application of Dormex at 0.50% showed a satisfactory fruit set, yield, and fruit weight in ‘Friar’ plum. Prebloom Dormex application had no significant effect on `Simka' plum fruit set or yield, but full bloom application decreased fruit set and yield.

EFFECTS OF HYDROGEN CYANAMIDE ON APPLE AND PLUM FRUIT THINNING

Influence of various concentrations of hydrogen cyanamide (HC) on fruit thinning of `Rome Beauty' apple (Malus domestica Borkh.), `Friar,' and `Simka' plums (Prunus salicina Lindley) were studied. A full bloom application of HC at all tested concentrations decreased `Rome Beauty' apple fruit set and yield, and increased fruit weight. Hydrogen cyanamide at 0.25% (V/V) resulted in adequate apple thinning, indicated by the production of an ideal fruit weight. Prebloom and full bloom applications of HC at greater than 0.75% reduced plum fruit set and yield in `Friar.' Full bloom application of HC at 0.25% to 0.50% showed a satisfactory fruit set, yield, and fruit size in `Friar' plum. Full bloom application decreased fruit set and yield in `Simka' plum. Hand thinning, as well as chemical thinning, is recommended for plums.

THE ROLE OF SPUR AND BOURSE LEAVES OF THREE APPLE CULTIVARS ON FRUIT SET AND GROWTH AND CALCIUM CONTENT

The development of a complete and healthy early season canopy of spur leaves, and later addition of bourse leaves, is essential for fruit set, fruit growth and quality in apple. The present study was undertaken to evaluate the temporal role of spur leaves and bourse shoots on fruit set, growth and return bloom in three apple cultivars and fruit Ca Level at harvest in two cultivars. Individual flowering spurs on mature wood of “Cox's Orange Pippin”, “Golden Delicious” and “Crispin” apple trees were modified by removing the spur leaves, the bourse shoot, or both, at full bloom and two, four and eight weeks afterwards. Leaf removal reduced fruit set, yield (as fruit number and not size), fruit calcium level at harvest, and return bloom. Defoliationhad its greatest effect on fruit calcium level when done early in the season and plots of this against treatment time suggested a curvilinear relationship. Return bloom was dependent on the presence of the bourse shoots on the spur but not on spur leaves. Return bloom of all three cultivars declined with the number of fruitlets per spur four weeks after full bloom.

Actographs for Recording Daily Activity of Plum Curculio (Coleopera: Curculionidae)

Two types of actographs were designed to study changes in daily activity of plum curculio, Conotrachelu8 nenuphar (Herbst), throughout two growing seasonsin southwestern Quebec. The technique is based on plum curculio’s thanatose behavior. During the time when adult plum curculio are active, they repeatedly climb up the walls of cages and drop to the floor. The rate at which they do so provides a measure of their activity. Two years’ data indicated that their activity patterns change throughout the growing season. Before apple fruit set, plum curculio dropped mostly during the night. During fruit set and June drop, they remained active throughout the day and night. During mid-summer, the pattern of activity was less predictable. Adults resumed nocturnal dropping activity during the fall.