Fruit Thinning Treatments Research Articles

Mitigation of severe water stress by fruit thinning in ‘O’Henry’ peach: Implications for fruit quality

Fruit thinning can be used to relieve water stress in peach but it is not known how fruit quality will respond under water limited conditions. To elucidate this, we applied, over the growing seasons of 2003 and 2004, irrigation and fruit thinning treatments to ‘O’Henry’ peach at the onset of Stage III of fruit development. The treatments were full irrigation (FI) and no irrigation (NI) with each receiving three crop load levels: light, commercial and heavy. Fruit size and fruit skin colouration were lower in NI than in FI but the following were higher in NI fruit: firmness, juice titratable acidity and electrical conductivity, and concentrations of dry matter and soluble solids. All the quality parameters were significantly correlated with tree water status, expressed as midday stem water potential. NI fruit matured 5–10 days later than FI fruit. The increased dry matter concentration, juice acidity, and electrical conductivity in NI fruit were indicative of lower quality at harvest. Choosing a light crop load was not effective in improving NI fruit quality except for the size. Since fruit size is the most important fruit quality attribute, its increase might compensate for yield losses resulting from heavy fruit thinning. Nevertheless, when heavy thinning is performed for mitigation of water stress in Stage III, the overall fruit quality will suffer if severe water stress is inevitable because of shortage or lack of irrigation water.

Fruit thinning in ‘Conference’ pear grown under deficit irrigation to optimise yield and to improve tree water status

SUMMARYA fruit thinning strategy is introduced for ‘Conference’ pear to mitigate water stress and to maximise yield. Three irrigation and four thinning treatments were applied. The three irrigation treatments were: full irrigation (FI); deficit irrigation, receiving 50% of the water in FI (DI-50); and deficit irrigation receiving 20% of the water in FI (DI-20). The four fruit thinning treatments were: no thinning (NT); light thinning (LT), leaving more than 80% of the crop load; medium thinning (MT) leaving 50% of the crop load; and heavy thinning (HT) leaving 20% of the crop load. All thinning treatments were combined with DI-20, but only NT and MT were combined with FI and DI-50. Fruit thinning improved fruit size in FI and DI-50, but is not recommended because of the high labour cost and reduction in total fresh-market yield. For DI-20, thinning increased the midday stem water potential ( stem), improved yield (with LT), and increased fruit size (with HT). A three-dimensional regression model was developed to optimise fresh-market yield by fruit thinning, and showed the impact of stem. Using the model, it was also possible to choose, for each value of stem, a suitable crop load to maximise the fresh-market yield.

Responses of apple fruit size to tree water status and crop load

The combined effects of irrigation rate and crop load on apple yield and fruit size were examined in two commercial apple orchards (cv. Golden Delicious) in a semi-arid zone. The irrigation rates applied were 1, 3 and 7 mm day(-1), and the two fruit thinning treatments involved adjusting crop load to 100 and 300 fruits per tree at Ortal and 50 and 150 fruits per tree at Matityahu. Unthinned trees served as the control. The fruit from each tree was picked separately, and fruit size distribution was determined with a commercial grading machine. Midday stem water potentials varied from -0.9 to -2.8 MPa, crop load varied from 80,000 to 1,900,000 fruit ha(-1) and crop yield varied from 10 to 144 Mg ha(-1). Midday stem water potential decreased with increasing crop load in all irrigation treatments at Matityahu, but only in the 1 mm day(-1) treatment at Ortal. The extent of the lowering of midday stem water potential by crop load decreased with increasing soil water availability. At both orchards, a similar response of total crop yield to crop load on a per hectare basis was observed. Mean fruit mass and relative yield of fruit > 70 mm in diameter increased with midday stem water potential, with the low crop loads having similar but steeper slopes than the high crop load. The responses of mean fruit mass and relative yield of fruit > 70 mm in diameter to midday stem water potential were similar at both orchards, perhaps indicating that thresholds for irrigation scheduling are transferable to other orchards within a region. Factors that may limit the transferability of these thresholds are discussed.

EFFECT OF FRUIT CROP LOAD ON PEACH ROOT GROWTH

Field experiments were conducted on mature, late-maturing peach trees (‘O' Henry’) to study the influence of assimilate availability on root growth. Crop load was used to vary assimilate availability by imposing three different fruit thinning treatments: thinned to commercial fruit loads, unthinned and completely defruited. Seven trees were used for each treatment, and four ingrowth root bags were buried per tree during four different periods of the growing season (corresponding to the three fruit growth stages and after fruit harvest). The bags were collected one month after burial and the root growth into each bag was determined from dry weight of all newly developed roots in a bag. Root growth values varied depending on crop load and fruit growth stage. During the first stage of fruit growth there was no effect of crop load on root growth. Root growth in all thinning treatments increased compared to the first stage and was significantly higher for the defruited trees. The root growth was minimal during the third stage of fruit growth in all the treatments. After harvest, root growth increased again in all the treatments. These experiments clearly demonstrated that there are seasonal patterns to root growth activity in peach trees and that crop load clearly influences the extent of that activity primarily during the late spring when the fruits are in the second stage of fruit growth.

Source - sink manipulation to increase melon (Cucumis melo L.) fruit biomass and soluble sugar content

Various source–sink perturbations were employed to alter partitioning to orange flesh melon (Cucumis melo L. reticulatus group) and thus to influence fruit biomass and soluble sugar content (indexed as total soluble solids of fruit juice, % TSS), with attention given to the timing of treatment application. A strong relationship existed between harvest index and fruit mass (r2 = 0.88) in control plants, whereas the correlation with fruit TSS was poor (r2 = 0.11). Augmentation of assimilate supply to fruit early in fruit development (before approx. 21 days before harvest, DBH) resulted in more fruit set and increased fruit biomass, whereas augmentation after 21 DBH resulted in increased fruit TSS. Thus, fruit biomass was increased (1644 cf. 1442 g FW per fruit for control, P = 0.02), but not TSS, on plants in which fruit set was delayed (source biomass increased, harvest index decreased from 59% for control to 38%). Treatment of plants with a cytokinin-based vegetative growth inhibitor at 14 DBH produced fruit with higher TSS (11.3 cf. 10.7% for control). Thinning fruit to leave 1 fruit per plant 1 week before harvest increased the proportion of fruit in a population that exceeded a quality control standard of 10% TSS from 20 to 80%. Variations in plant response with timing of treatment application are interpreted in terms of fruit development (cell division, cell expansion, and sugar accumulation phases). Although a detriment to yield (15 cf. 31 t/ha for control), the fruit thinning treatment was recommended for commercial use and a simple model was developed to calculate the required farm-gate price of fruit to make thinning economically viable.

Individual and combined effects of shading and thinning chemicals on abscission and dry-matter accumulation of ‘Royal Gala’ apple fruit

SummaryShade and chemical thinning treatments were applied to mature ‘Royal Gala’/M.26 apple trees either alone or in combination to study their effects on the pattern of abscission and growth of spur fruit. Natural fruit drop occurred in two distinct waves in both years; the first wave peaked 20 d after bloom (DAB) at a weekly abscission rate of c 15% in both years. The second wave of fruit drop in 2001 occurred earlier and was more intense than in the previous season. Application of NAA as a bloom thinner increased the maximum weekly abscission rate during the first wave of fruit drop in both years. Chemical fruit thinning treatments (Carbaryl in 2000, BA or delayed lime sulphur in 2001) had no effect on abscission or growth of spur fruit. Covering trees with 80% shade cloth for 3 d (2000) or 5 d (2001) stimulated a wave of fruit abscission that peaked c 10–15 d after removal of the cloth. Shade during the period from 20–25 DAB stimulated more fruit drop than earlier shade treatments, resulting in weekly abscission rates as high as 70%.There were no additive effects of combining thinning chemicals and shade treatments on abscission of fruit from spurs. However, additive effects of shade and thinning treatments were observed when measured as whole-tree crop density values, indicating that abscission of fruit from one-year wood was stimulated when low light conditions preceded application of (fruit) thinning chemicals. Shading trees from 34–39 DAB in 2000 resulted in a transient reduction and subsequent increase in the rate of dry-matter accumulation in fruit that were retained. Considerable challenges lie ahead in developing models of fruit growth that can account for the inter-dependent effects of light and crop load on fruit abscission and development that exist within an orchard environment.

結果節位の異なるイチジク果実の形質と糖集積に及ぼす摘果の影響

イチジク'桝井ドーフィン'を用い, 結果枝内の第7節以下のすべての果実を横径が約4mmに達した結果期に摘果して, 第8節と第13節の果実の形質と糖集積に及ぼす影響を調査した.1. 第8節と第13節の果実が結果から成熟までに要した日数は73∿74日で, 摘果区と無処理区との間に差はなかった.結果後の果実肥大において, 第8節の果実では摘果処理の影響が小さかったが, 第13節では果径が肥大初期から大きくなる傾向が認められた.2. 無処理区の収穫果実は, 第8節と第13節の果実は第3節の果実に比べ横径と果実重が著しく小さく, 肥大が劣った.第8節, 第13節の果実は, 第3節に比べて果皮色のE値が高く着色が劣り, 小果, 果托の糖度も低かった.果実の硬度は, 節位間に差がみられなかった.3. 摘果区では, 第13節の収穫果実の横径と果実重が無処理区より大きくなり, 果肉内では小果よりも果托の重量が増加した.果皮色のE値は, 第8節では摘果区が無処理区より低くなって着色が優れ, 第13節でも摘果区が低下傾向となった.果実の硬度は, 第8節, 第13節の両節位とも処理区間に差がなかった.4. 摘果区では, 第8節, 第13節の小果および果托で無処理区に比べ単位重量当たりの果糖, ブドウ糖含量が増加した.また, 部位ごとの重量から換算した糖の総量も無処理区より多くなり, 特に, 重量増加が顕著であった第13節の果托で糖の集積が促進された.

Quantifying sink and source limitations on dry matter partitioning to fruit growth in peach trees

We describe an approach for determining the degree of sink and source limitations on peach (Prunus persica L. Batsch) fruit growth during several growth periods. Source limitations on fruit growth may be due to either a shortfall in assimilate supply within the tree (supply limitation) or to a deficiency in the capacity of the translocation system to deliver assimilates in sufficient quantity to support the maximum fruit growth rate (transport/competition limitation). To ascertain the potential maximum rate of fruit growth, fruit thinning treatments were used. One month after bloom, the number of fruits per tree was adjusted to between 50 and 700 on an early and a late maturing peach cultivar (cvs Spring Lady and Cal Red, respectively). Rates of potential sink demand, potential source supply and actual fruit growth were estimated from sequential harvests of all fruits on 42 trees on two (Spring Lady) and three (Cal Red) dates. These values were used to estimate the proportion of potential growth achieved, and the supply and transport/competition limitations on fruit growth. The results indicated that source limitations were significant on trees with moderate to high fruit numbers. These source limitations were due to supply limitations during all harvest intervals and to transport/competition limitations during the early harvest intervals. Sink limitations occurred to the greatest extent during the mid‐period of fruit growth on the later maturing cultivar.

Nutrient Concentration and Fruit Thinning Affect Shelf Life of Long English Cucumber

Long English cucumber (Cucumis sativus L.) plants were treated with one of three nutrient concentrations in combination with two fruit thinning treatments forming a 3 × 2 factorial greenhouse experiment. High nutrient concentration enhanced fruit color at harvest and prolonged shelf life but reduced marketable fruit per plant. Thinning of one-third of the fruit from the main stem and laterals had a similar effect. Cucumbers harvested from the upper canopy generally had longer shelf life than those from the lower canopy. Shelf life was correlated with fruit color at harvest.

ウンシュウミカン若木の着果程度及び摘果が果実の形質, 翌年の着花などに及ぼす影響

Six-year-old trees of‘Miyagawa Wase’, an early ripening satsuma mandarin, bearing various fruit loads under natural condition were selected (non-fruit-thinning tree group). Trees in almost the same range of fruit load as in the non-fruit-thinning tree group were obtained by thinning fruits on heavily loaded trees (fruit-thinning tree group). The influences of fruit load and fruit thinning treatments on the fruit character, flower bud formation in the following season and the other components were investigated.1. The Brix of juice was higher with an increasing index of fruit load (No. of fruits per 10, 000 leaves) in the fruit-thinning tree group. However, the changes in Brix with increasing index of fruit load were small and the correlation between these two components was very low in the non-fruit-thinning tree group.2. In the lower range of index of fruit load, the Brix of juice in fruit-thinning trees was lower than that in non-fruit-thinning trees which were similarly loaded. When fruits were mixed and classified by fruit size, the Brix of larger fruit was lower in both group. Also the Brix of fruit in the fruit-thinning tree group was lower than that of the same size fruits in the non-fruit-thinning tree group.3. The more severe fruit thinning resulted in a lower Brix value independent of the fruit load in both groups of trees (the intensity of fruit-thinning treatment in non-fruit-thinning tree group was considered as zero percent).4. Acid concentration of juice correlated positively with index of fruit load in both tree group. When fruits were mixed and classified by fruit size, the acid concentration of similar size fruit was almost the same in both group. Fruit thinning therefore, seems to have little affect on the acid concentration of juice.5. The average weight per fruit decreased with increasing fruit load in both tree group, with no clear difference between the two tree group.6. In the non-fruit-thinning tree group, the summer shoot leaves in that year sprouted considerably regardless of fruit load. There was less sprouting in the fruit-thinning tree group and this decreased with increasing fruit load, to almost no sprouting at a index of fruit load of above 600.7. Trees of both groups having a low fruit load flowered abundantly much in the following year. The flowering in the fruit-thinning tree group was lower than that in the non-fruit-thinning tree group at similar fruit load. The flowering was insufficient to expect a normal yield at a index of fruit load of more than 550 in the non-fruit-thinning tree group, and more than 450 in the fruit-thinning tree group.

Effects of Fruiting, Pruning, and Nitrogen Fertilization on Shoot Growth of ‘Empire’ Apple Trees1

Abstract Three fruit thinning, 2 pruning, and 2 nitrogen fertilization treatments, in factorial combination, were established in a 7-year-old orchard of ‘Empire’ apple (Malus domestica Borkh.)/Malling Merton 106. The pruning and N fertilization treatments were continued over a 4-year period; the initial fruit-thinning treatments induced significantly different bearing patterns that persisted through the 4 years and no additional thinning was done. The thinning treatments resulted in significant differences in yield, but pruning and N had little effect. Total shoot growth/tree was unaffected the first year, but large differences developed in the succeeding years. Crop load and N had major effects on shoot growth while the effect of pruning was minor. Total shoot growth was more closely related to shoot numbers than to mean shoot length and was negatively correlated with the previous year’s crop.

Branch Samples for Yield and Fruit Size Comparisons in Apple1

Abstract Differential fruit thinning treatments produced differences in yield, fruit numbers, and fruit size in 2 ‘McIntosh’ and 1 ‘Empire’ apple (Malus domestica Borkh.) orchards. Fruit set, crop load, and fruit size data calculated from branch samples paralleled corresponding data for whole trees.