Bourse Shoot Research Articles

Transport and metabolism of exogenously applied gibberellins to Malus domestica Borkh. cv. Jonagold

The radio-labeled gibberellins GA1, GA3,GA4, and GA7 were applied to intact developing applefruits (Malus domestica Borkh. cv. Jonagold) during theperiod when GAs are suggested to inhibit flower bud induction for the followingyear. Radioactivity from these compounds was found to be transported intoadjacent tissues as there are pedicels and bourses (4%). Application topedicels, after removal of the fruits, enhanced the transport into adjacentbourses up to 11%. The bud-carrying lateral bourse shoots contained onlyminor amounts of radioactivity on average 0.4% in both cases. Theseexport rates were identical, 1 or 5 days after application.After application of the corresponding deuterium-labeled GAs and analyses bymass spectrometry the specific metabolization of GA1 toGA1 13-O-glucoside and of GA3 to GA313-O-glucoside was demonstrated. Additional metabolites of GA1 andGA3 were not detected. After fruit application of GA3 theratio of GA3 to GA3 13-O-glucoside was found to be 1:2 inthe fruit. Pedicel application led to ratios of 1:4 and 1:5, respectively, inthe pedicel and in the adjacent bourse. After the application of GA4and GA7, neither glucosylation products nor other GA-like metabolitescould be identified.This is the first report of the metabolism of GAs to GA 13-O-glucosides indeveloping apple fruits. The possible function of the GAs as a signal in flowerbud formation for the following year is discussed.

Benzyladenine as A Chemical Thinner for `McIntosh' Apples. II. Effects of Benzyladenine, Bourse Shoot Tip Removal, and Leaf Number on Fruit Retention

Experiments were conducted to evaluate the effects of BA, removal of bourse shoot tips including only folded leaves and growing point, and different numbers of leaves per fruit on fruit retention and fruit development in `More-Spur McIntosh'/Malling 7 (M.7) apple trees [Malus sylvestris (L.) Mill var. domestica (Borkh.) Mansf.]. Removal of the bourse shoot tip increased fruit retention, whereas BA thinned fruit regardless of whether shoot tips were removed or not. There was no interaction between BA application and shoot tipping. BA thinned fruit only when one leaf per fruit was on a girdled small fruiting branch, but not when leaf number per fruit was two or greater. Fruit weight and soluble solids concentration increased dramatically with increasing leaf number per fruit. BA reduced fruit growth rate when <16 leaves per fruit were present on the girdled branches between 3 and 7 days after treatment, but it did not affect fruit growth rate when 32 leaves per fruit were on the girdled branches. Increasing leaf number also increased viable seed number per fruit while decreasing the number of aborted seeds, but it had no effect on the number of total seeds per fruit. BA reduced the number of viable seeds per fruit only when the number of leaves per fruit was less than four. Results suggest that BA thins apple fruit mainly by reducing carbohydrates available to developing fruitlets. Chemical name used: N-(phenylmethyl)-1H-purine-6-amine [benzyladenine (BA)].

Effect of Benzuladenine on Apple Fruit Thinning and Its Mode of Action

Benzyladenine (BA) applied at the 10-mm stage at 50 and 100 mg·L-1 thinned fruit, increased fruit size, and caused seed abortion. The translocation of 14C-sorbitol from leaves to fruit was promoted by B A application to the fruit, but not when BA was applied to the leaves. Therefore, it is unlikely that BA causes thinning directly by restricting photosynthate movement into the fruit. Net photosynthesis was decreased and dark respiration was increased when temperature following BA application was high (30 °C), whereas there was no effect when temperature was lower (20 °C). The seed number in abscising fruit was greater in BA-treated fruit than in control fruit. The number of viable seeds in BA-treated fruit was reduced. Tipping the bourse shoot increased fruit set, regardless of BA treatment. Benzyladenine thinned fruit when only one leaf was on the girdled fruiting spur, but not when leaf number was greater than two. Reduction of carbohydrates available for fruit appears to be the primary factor responsible for the thinning induced by BA. E-mail Yuan@pssci.umass.edu

Effect of Benzyladenine (BA) on Fruit Thinning and Carbohydrate Status in Apples

BA applied at the 10-mm stage at 50 and 100 ppm thinned, increased fruit size, and seed abortion. Net photosynthesis was decreased and dark respiration was increased when temperature following BA application was high (30°C), whereas there was no effect when temperature was lower (20°C). The seed number in abscising fruit was greater in BA-treated fruit than in control fruit. The number of viable seeds in BA-treated fruit was reduced. Tipping the bourse shoot increased fruit set, regardless of BA treatment. BA did not thin fruit with 25 leaves or greater. The translocation of 14C-sorbital from leaves to fruit was promoted by BA application to the fruit, but not when BA was applied to the leaves. The thinning induced by BA will be discussed in relation to available carbohydrate.

Crop loading studies with ‘Royal Gala’ and ‘Braeburn’ apples: Effect of time and level of hand thinning

Abstract The effects of time and level (fruit number/tree) of hand thinning on fruit size were investigated for ‘Royal Gala’ and ‘Braeburn’ apple (Malus domestica (Borkh.)) trees growing on dwarfing rootstocks. Early thinning resulted in larger fruit at harvest in three separate experiments whereas the number of fruit per tree had a significant influence on mean fruit weight in only one experiment. Compared to thinning at full bloom (FB), mean fruit weight of ‘Royal Gala’ at harvest was reduced by 16% when thinning was delayed by 3–4 weeks after full bloom (WAFB), with a much smaller decrease in weight with further delay. ‘Braeburn’ gave the opposite pattern, with the greatest loss in mean fruit size at harvest being recorded when thinning was delayed by 8 WAFB. Thinning 4 or 8 WAFB resulted in a 17% decrease in leaf area per tree of ‘Royal Gala’ compared to thinning at FB, whereas laterthinning of ‘Braeburn’ reduced leaf area per tree by 6% per 4 weeks delay in thinning. Removal of fruit from ‘Braeburn’ spurs at FB reduced spur leaf size, king flower receptacle diameter/dry weight, and bourse shoot length on that spur in the year after treatment compared to removal at a later time.

The Bases of Productivity in Apple Production Systems: The Role of Light Interception by Different Shoot Types

Although apple (Malus domestica Borkh.) system yield differences are generally related to whole-canopy light interception, this study tested the hypothesis that these orchard yields are related primarily to total light intercepted by the spur canopy. Seasonal leaf area development of different shoot types, exposed bourse shoot leaf net photosynthesis, fruit growth, whole canopy light interception (by image analysis of fisheye photographs) and relative light interception by different shoot types (by a laser assisted canopy scanning device) were estimated within four 14-year-old `Empire' apple production systems (slender spindle/M.9, central leader/M.7, central leader/M.9/MM.111 and Y-trellis/M.26). The final LAI values were CL/M.7 = 1.8, CL/9/111 = 2.3, SS/M.9 = 2.6 and Y/M.26 = 3.6. Exposed leaf net photosynthesis showed few differences and was not dependent upon the production system. Yields of the pyramidal shaped tree forms were 40 to 42 t·ha-1 while Y-trellis produced 59 t·ha-1, with similar fruit sizes. Again, yields were primarily related to the percentage of light intercepted by the whole canopy, 48% to 53% for conic forms versus 62% for the Y-trellis system. Laser analyses showed that the Y-trellis system intercepted about 20% to 30% more light with the spur canopy than the conic tree forms, supporting the hypothesis. Yields were better correlated with spur canopy LAI and spur canopy light interception than with extension shoot canopy LAI and light interception.

Mineral accumulation in apple fruit as affected by spur leaves

The mineral composition of apple ( Malus domestica Borkh.) fruit from spurs with artificially adjusted spur leaf areas was examined throughout fruit development. Primary leaf and/or bourse shoot removal at bloom or petal fall reduced Ca content during the growing season on ‘Gala’, ‘Golden Delicious’ and ‘Royal Gala’. Bourse shoot removal 75 days after full bloom had a similar but less pronounced effect on final fruit Ca content for ‘Royal Gala’. Primary leaves assisted movement of Ca into fruit earlier and were more efficient on a per leaf area basis throughout fruit growth than bourse leaves. Fruit Mg contents showed similar but less consistent responses to spur leaf removal compared with Ca. Fruit K contents and fruit fresh weight were similar from spurs whose primary spur or bourse shoots/leaves had been removed.

321 GIBBERELLIN METABOLISM AND FLOWERING IN APPLE

Some apple cultivars are biennial. Experiments with the facultatively parthenocarpic apple cultivar `Spencer Seedless' indicated that seeds are responsible for inhibiting flowering (Chan and Cain, Proc. ASHS 91:63-68, 1967). Because gibberellin inhibits flowering in apple, seed GAs may be responsible for biennial bearing, or seeds may affect metabolism of GAs in bourse shoots. To obtain additional information, 14C - G A12 was injected into seeds or bourse shoots of `Spencer Seedless' and the metabolites were extracted after 24 or 48 hr. Metabolites moved from seeds to bourse shoots and vice versa in 1992, only the most polar compound(s) being transported. However, transport was not observed in 1993. Five metabolites of 14C - G A12 were found in apices following injection, 5 to 7 in seeds. Two metabolites occurred in fruit flesh following seed treatment. The presence of seeds appeared to have no qualitative effect on metabolism in the bourse shoot, although the metabolites have not yet been identified.

295 EFFECTS OF SEED NUMBER, TIME OF DEFRUITING, AND BOURSE SHOOT LENGTH ON FLOWERING IN APPLE

Chan and Cain (Proc. ASHS 91:63-68, 1967) demonstrated that seeded apple fruits inhibited flowering, whereas seedless ones did not. `Spencer Seedless' spurs bearing seeded or seedless fruits were defruited at various times after anthesis in 1989-1991 and fruit weight, seed number and bourse shoot length recorded, as well as repeat bloom. Similar defruiting treatments were also applied to entire `Paulared (all seeded fruits) trees in 1991 and 1992. In all years spurs bearing seedless fruits flowered the following year, regardless of defruiting time, shoot length or fruit weight per spur. Flowering of spurs bearing seeded fruits decreased as defruiting was delayed. In all years over 90% of spurs bearing fruits containing a total of 5 seeds or less flowered, whereas 90% of those with more than 5 seeds remained vegetative. Flowering was not correlated with shoot length or fruit weight. Bearing spurs of `Paulared' flowered when whole trees were defruited within 60 days after anthesis, but flowering was greatly inhibited when fruits were left on for 97 and 74 days in 1991 and 1992, respectively.

LEAF AND FRUIT DEVELOPMENT OF `EMPIRE' APPLE TREES AS INFLUENCED BY SHADING AND FOLIAR MICRONUTRIENTS.

Lower scaffold branches of `Empire'/M.7 apple trees which were planted in 1975 and trained as Central Leaders were shaded or left exposed from 1986-1988. Foliar micronutrient sprays of N, Zn and B were applied 3 times in the early season of each year to both shaded and exposed scaffold branches in an attempt to improve spur vigor. In 1988 spur and bourse shoot leaf area development and fruit growth were monitored. Shading resulted in greater initial spur leaf area at 3 weeks after bloom but shorter leaf duration. Spurs on shaded branches had lost 2/3 of their leaf area by 11 weeks after full bloom while exposed branches had lost only 25%. Bourse shoot leaf area was greater on exposed branches throughout the season. Foliar sprays of micronutrients did not increase leaf area or leaf duration of either spur leaves or bourse shoot leaves. Fruit growth rate was reduced by shading most in the early season. Final fruit size, color, soluble solids and dry matter were reduced by shading. Foliar micronutrient sprays did not affect fruit growth rate any time during the season or final fruit size, color, soluble solids and dry matter. There was also no interaction of shading and foliar nutrition on fruit size or quality. It appears that the negative effects of shading on spur vigor and fruit quality cannot be reversed by foliar micronutrient sprays.

Effect of CPPU on fruit and shoot growth of apple

The effects of CPPU on the growth of fruits and bourse shoots of apple were examined by targeted applications of 20 mg I“1 CPPU to fruitlets and/or bourse-shoot and spur leaves. Treating fruitlets and fruitlets-plus-leaves stimulated fruit growth to a similar extent; fruit growth rate was temporarily suppressed when only the leaves were treated. Conversely, bourse shoot growth was stimulated by leaf and leaf-plus-fruit treatments. All CPPU applications reduced the content of fruit soluble solids and induced a paler yellowish- green fruit ground colour.

Effect of previous-season and current light environments on early-season spur development and assimilate translocation in ‘Golden Delicious‘ apple

Flowering spurs of ‘Golden Delicious’ apple showed variation in patterns of leaf area development during the period between petal fall and June drop. Differences were the result of changes to bourse leaf area in response to shading of the spur occurring in the previous season or during current-season development. Bourse leaf area was lowest on spurs which were shaded in the previous season. These spurs developed bourse shoots with fewer leaves and which ceased extension growth earlier than bourse shoots on well illuminated spurs or those temporarily shaded in the current season. Dry weight per unit leaf area of spur leaves was markedly greater for well exposed spurs than for spurs shaded in either the previous or the current season. Similar responses were observed with bourse-shoot leaves in the period five to eight weeks after full bloom. Patterns of allocation of 14C-labelled photoassimilate derived from spur or bourse leaves, two weeks after full bloom, were not affected by shade treatments. In contrast, the temporary shading of well-exposed spurs, five weeks after full bloom, significantly reduced the proportion of spur leaf assimilate partitioned to the fruitlets, compared with unshaded spurs. A similar but non-significant trend was also evident for assimilate originating from the bourse leaves. The early termination of bourse shoot growth on spurs which were shaded in the previous season resulted in more bourse-derived assimilate being partitioned to fruitlets, in comparison with spurs from well-exposed sites, the differences increasing with time after full bloom. Overall, shade-induced effects on spur ‘vigour’ appeared to be related to changes in total spur photosynthetic potential rather than to qualitative differences in the partitioning of assimilates.

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.

The role of spur and bourse leaves of three apple cultivars on fruit set and growth and calcium content

SummaryIndividual 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. Defoliation had 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.

Spur Development of `Delicious' Apple as Influenced by Position, Wood Age, Strain, and Pruning

The role of spur leaves in bud and fruit development on two spur-type `Delicious' apple strains (Malus domestica Borkh.) and factors affecting spur development were studied. Reducing spur leaf area on vegetative spurs in August reduced the number of spurs that flowered the following year but did not affect flower size. On spurs that did flower, leaf area reduction the previous year did not influence leaf number or area, but the bourse shoot leaf area was reduced. Spur bud diameter, leaf area, size, specific leaf weight (SLW), and leaf dry weight were larger on 2-year-old vegetative spurs than on 1- or 3-year-old spurs. Within each age section of a limb, spur leaf number, area, size, SLW, and bud diameter decreased from the apical to basal positions on the limb. Flower number did not vary within a limb section, but fruit set was lower on the most apical and basal spurs compared to midshoot spurs. Fruit size was largest at the apical end of each limb section and was smallest at basal positions. These relationships were not affected by strain, tree age, or orchard location. Summer pruning at 30 days after bloom tended to increase leaf number, area, size, and spur length compared to unpruned trees or pruning later in the season but did not influence spur bud diameter.

EFFECTS OF CHRONIC SHADE AND FOLIAR NUTRIENT SPRAYS ON APPLE SPUR VIGOR AND PERFORMANCE

Eleven year-old Empire/M.7 apple trees were shaded continously for 4 years with half-tree shading cages. Shading reduced primary spur leaf duration, bourse shoot leaf area, specific leaf weight, spur diameter and bud diameter. Over the four years, shaded spurs continued to increase in length but spur diameter increased very little resulting in long and brittle spurs. However, shaded spurs continued to flower and set fruit. Leaf area development was similar inside and outside the cages at one week after bloom but by 2 weeks after bloom, spurs inside the cages had significantly lower leaf area. Shading reduced fruit set, fruit size, fruit color, fruit soluble solids and fruit dry matter. Fruit growth rate was reduced by shading early in the season but was no different than the unshaded controls by 4 weeks after full bloom.In an attempt to reverse the negative effects of shading on spur vigor, foliar urea, zinc-EDTA and solubor were sprayed 3 times during the early growing season each year. Rather than increasing spur leaf area, foliar nutrient sprays significantly reduced bourse shoot leaf area and did not increase the duration of primary spur leaves. Although foliar nutrients reduced total spur leaf area, they improved fruit size, color and soluble solids slightly.

Seasonal Development of the Leaf Canopy of ‘Macspur McIntosh’ Apple Trees

Abstract Leaf canopy development of 7- and 10-year-old- ‘Macspur McIntosh’/M.7 apple (Malus domestica Borkh) trees was studied in 1986. All growing points were counted on six trees of each age at budbreak and at appropriate intervals thereafter. The growing points were divided into old spurs, new spurs, terminal shoots, lateral shoots, and bourse shoots. Only old spur leaves were present from budbreak to pink; at pink, terminal shoots could be distinguished; at petal fall, the other three types could be identified. Shoot leaves averaged nearly 50% larger than spur leaves and made up 36.8% of the leaf numbers and 45.7% of the leaf area at full leaf. The leaf canopy was 10% complete at full bloom and 23% complete at petal fall. Total leaf area/tree increased 8-fold in the 4 weeks after full bloom.

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.

Translocation properties of carbaryl in relation to its use as an apple fruitlet thinner

SummaryLocalized treatment of either fruitlets, pedicels or bourse shoot leaves of cv Discovery apple trees with 2 100 ppm carbaryl caused significant fruitlet abscission. Whereas carbaryl applied to a pedicel moved in significant amounts into the fruitlet, carbaryl applied to the fruitlet itself or to the bourse shoot leaves was not translocated. Carbaryl applied to a fruitlet did not enter the seeds. A possible mode of action is discussed and some practical implications considered.

Effect of Spur Defoliation and Ringing during Bloom on Fruiting, Fruit Mineral Level, and Net Photosynthesis of ‘Golden Delicious’ Apple1

Abstract Leaf areas on individual spurs were modified in the pink stage of flower development on ‘Golden Delicious’ apple (Malus domestica Borkh.), and the effects on fruiting, mineral content, and net photosynthesis (Pn), of leaves on those spurs determined. Removal of a 3mm-ring of bark from the spur increased initial fruit set, determined 1 week after petal fall, compared to normal spurs. The combination of ringing and removal of all leaves resulted in a complete loss of fruit. Final fruit set was reduced by any treatment involving ringing, reduction in spur leaf area, or injury to the stigmas. The greatest number and total weight of fruit at harvest were given by undefoliated, unringed spurs where the bourse shoot was allowed to develop. Ringing reduced Pn at petal fall but had no effect later in the season. Presence of the bourse shoot reduced Pn of spur leaves in early June. Spur leaves on fruiting trees had an important localized influence on fruit set, ultimate fruit size, and fruit Ca level of fruit produced on that spur.