Fruit thinning in ‘Conference’ pear grown under deficit irrigation: Implications for fruit quality at harvest and after cold storage

Fruit thinning in pear is feasible for mitigation of water stress effects. However, it is not well known how fruit quality at harvest and after cold storage is affected by pre-harvest water stress. Even less is known about the effects of fruit thinning on quality under these circumstances. To elucidate these, we applied deficit irrigation (DI) and fruit thinning treatments to ‘Conference’ pear over the growing seasons of 2008 and 2009. At the onset of Stage II (80 and 67 days before harvest in 2008 and 2009, respectively), two irrigation treatments were applied: full irrigation (FI) and DI. FI trees received 100% of crop evapotranspiration (ETc). DI trees received no irrigation during the first three weeks of Stage II to induce water stress, but then received 20% of ETc to ensure tree survival. From bud-break until the onset of Stage II and during post-harvest, FI and DI trees received 100% of ETc. Each irrigation treatment received two thinning levels: no thinning leaving commercial crop load (∼180 fruits tree⁻¹), and hand-thinning at the onset of Stage II leaving a light crop load (∼85 fruits tree⁻¹). Under commercial crop loads, DI trees were moderately water-stressed and this had some positive effects on fruit quality. DI increased fruit firmness (FF), soluble solids concentrations (SSC) and acidity at harvest while no changes were observed in fruit maturity (based on ethylene production). Differences in FF and acidity at harvest between FI and DI fruit were maintained during cold storage. DI also reduced fruit weight loss during storage. But fruit size was reduced under DI. Fruit thinning under DI resulted in better fruit composition with no detrimental effect on fresh-market yield compared to un-thinned fruit. Fruit size at harvest and SSC values after five months of cold storage were higher in fruit from thinned trees than fruit from un-thinned trees. Fruit thinning increased fruit ethylene production, indicating advanced maturity. This may lead to earlier harvest which is desirable in years with impending drought. Fruit thinning is therefore a useful technique to enhance pear marketability under water shortage.     

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.     

Site and fruit maturity influence on the quality of European plum in organic production

Information available on the role of site and fruit maturity in the quality of European plums in organic production has not been studied to date. European plum cv. ‘Green Gage’ grown in organic production was harvested in order to study the effect of site and fruit maturity on fruit quality. At harvest, significant differences were found in fruit weight, colour, firmness and TSS between harvest dates, whereas significant differences were found in fruit weight, colour, firmness and fruit Ca content between sites. Differences remained during storage. Fruit weight loss during storage was affected by site. Fruit with high Ca content showed higher firmness both at harvest and during storage. Harvest moment should not be chosen according to date, since differences between sites at the same date have been found. Firmness and colour parameters a* and h° would be useful to distinguish maturity at harvest between different sites and harvest dates. Linear regression between h° and firmness at harvest would allow the use of the h° colour parameter as a non-destructive measurement to distinguish maturity. Organic orchards should keep a minimum level of Ca in order to assure a slower fruit softening during storage.     

Changes in ripening behavior of ‘d'Anjou’ pears (Pyrus communis L.) after cold storage

‘d'Anjou’ pear fruit, harvested at optimum maturity with flesh firmness of 6.8 kg, were stored at ?1.1°C. Fruit were ripened at 20°C for 15 days following storage for 1–8 months. Dessert qualities were evaluated organoleptically on Day 10 of each ripening period. Changes in fruit firmness, extractable juice, titratable acids, solubl solids, respiration, ethylene production and internal ethylene were determined daily during each ripening period. Fruit firmness declined continually from 6.8 kg at harvest to 4.5 kg after 8 months of storage. Fruit stored for 2–8 months softened with a similar pattern during a 15-day ripening period at 20°C, while fruit stored for 1 month softened at a slower rate during ripening to 3.2 kg, with a coarse and dry texture after 15 days at 20°C. Fruit stored for 2–4 months ripened with the desirable buttery and juicy texture, while those stored for more than 5 months ripened with a coarse or mealy and dry texture. The buttery and juicy texture was highly correlated with a lower extractable juice, which could be used for quantitative determination of storage life based on ripened fruit quality. Changes in titratable acids and soluble solids during each ripening period were not associated with changes in dessert qualities of the ripened pears. Rates of respiration, ethylene production and internal ethylene during ripening at 20°C varied with duration of storage, but were not associated with changes in dessert qualities of the ripened fruit.     

Flower thinning method affects mineral composition of `Braeburn' and `Fiesta' apple fruit

Summary

Fruit mineral concentrations measured at harvest can have major effects on apple fruit quality on the tree or during storage. Orchard practices must therefore seek to optimize fruit mineral composition. The purpose of this study was to describe and elucidate the effects of hand thinning on whole trees and individual spurs on apple fruit mineral composition. Two methods of flower and fruitlet thinning were compared with no thinning on `Braeburn' and `Fiesta' apple trees. Alternate whole flower/fruitlet clusters or all but one flower/fruitlet within every cluster were removed at full bloom or 14±21 d after full bloom. Alternate-cluster thinning reduced final fruit numbers per tree and fruit Ca concentrations by up to 22%, while increasing final fruit size by up to 21%, compared with no thinning. These effects on fruit Ca concentrations were also measured across a range of fruit size classes. Within-cluster thinning at full bloom or up to 21 d after full bloom also reduced fruit numbers per tree but increased fruit size substantially, by up to 65% compared with no thinning, this effect being less for later thinning. However, fruit mineral concentrations were not influenced by this treatment. Some fruiting spurs were singled to one fruit 14 d after full bloom on alternately flower cluster thinned trees and on trees that had not been thinned at bloom, and compared with unthinned spurs on the same trees. Fruit Ca concentrations, primary spur leaf areas and primary spur leaf areas per fruit were greater for spurs bearing a single fruit (achieved by thinning manually or through natural abscission) than for multi-fruited spurs on the same trees. Spurs bearing one fruit on unthinned trees had greater fruit Ca concentrations, primary spur leaf areas and primary spur leaf areas per fruit, but lower fruit weight than the same spurs on alternate-cluster thinned trees. However, spurs on unthinned and alternate-cluster thinned trees with the same primary leaf areas per fruit had similar final Ca concentrations. Fruit size and crop loads were found not to be important in explaining fruit Ca concentration differences between thinning methods. However our results suggest that thinning method may affect Ca accumulation in apple fruit by altering the relationship between fruit numbers and leaf areas on individual spurs.     

Partial rootzone drying maintains fruit quality of ‘Golden Delicious’ apples at harvest and postharvest

Partial rootzone drying (PRD) has been evaluated at harvest, but its effects on apple fruit postharvest life is little known for apples grown in semi-arid regions. The objective of this study was to test the hypothesis that water savings via PRD may affect fruit quality at harvest and postharvest-life of ‘Golden Delicious’ apples grown in a semi-arid region. The experiment was conducted from 2005 to 2007. The irrigation treatments were commercial irrigation as control (CI) and PRD. After 3 years of evaluation, fruit quality at harvest, measured as fruit weight, flesh firmness, and total soluble solids concentration, was similar between CI fruit and PRD fruit. Dry matter concentration (DMC) was higher in PRD fruit than in CI fruit in 2005. The fruit quality after 18 days storage at room temperature (13–18 °C and 51–56% relative humidity) was similar between CI fruit and PRD fruit. The DMC was the highest in PRD fruit in the 2005 and 2007 growing seasons, and tended to be higher in PRD fruit than in CI fruit in 2006. Total soluble solids concentration was ≈8.7% higher in PRD fruit than in CI fruit in 2007. Fruit weight loss was similar between treatments. This study suggests that water deficit via PRD did not damage fruit quality at harvest or after storage at room temperature. Additionally, PRD irrigation saved about 3240 m³ of water per hectare. Therefore, PRD can be recommended for commercial use in semi-arid regions and to those growers interested in either long-term storage or distant markets.     

Improvement of fruit quality and storage potential of ‘Braeburn’ apple through deficit irrigation

Summary

We explored the potential of deficit irrigation (DI) applied at different times during the growing season for improving fruit quality and storage potential of ‘Braeburn’ apple growing in a commercial orchard. Because DI often reduces fruit size, effects of fruit size on fruit quality were also examined. The irrigation treatments were: commercially irrigated control (C), early deficit irrigation (EDI) applied from 63 to 118 d after full bloom (DAFB), and late decifit irrigation (LDI) applied from 118 DAFB to final harvest on 201 DAFB. Both EDI and LDI improved fruit quality in terms of increases in: dry-matter concentration (DMC) at harvest, flesh firmness, total soluble solids, and total soluble sugars both at harvest and after storage. The DI fruit had less weight loss during storage than did C fruit. Deficit irrigation affected the concentrations of a few individual aroma volatiles but not total volatile concentration. Incidence of physiological disorders was not affected by irrigation treatments. Mean fruit weight was lower in DI than in C but the difference was not significant. Among the quality attributes studied, only firmness and DMC were affected by fruit size with their values being higher in smaller fruit.     

浸钙对猕猴桃果实硬度变化影响的生化机制

猕猴桃果实在贮藏过程中硬度下降分为两个明显的阶段，第一阶段硬度下降较快，主要与淀粉的快速水解有关，由于采后浸钙不能有效地降低淀粉酶的活性，因而钙处理对第一阶段硬度下降的影响不大。第二阶段的硬度下降主要与果胶物质的水解有关，钙处理后的果实，多聚半乳糖醛酸酶（ＰＧ）的活性降低，非水溶性果胶物质的降解及水溶性果胶物质的上升速度变慢，从而有效地减缓了果实的软化速度。钙处理对猕猴桃果实的ＡＣＣ氧化酶及纤维素酶的活性没有明显的影响。     

猕猴桃总淀粉酶活性与果实软化的关系

猕猴桃采后的软化过程分为两个明显的阶段，其中第一阶段果实的快速软化与淀粉酶活性的上升所引起的淀粉的快速降解显著相关（Ｒ＝０．９９）。用机械伤或乙烯处理可提高淀粉酶的活性，加速淀粉的降解，从而促进了果实的软化。与冷藏相比，气调贮藏可明显地阻止淀粉酶活性的上升，减少淀粉的降解，因而较好地保持果实的硬度。     

苹果采收适期与果实生物学指标的相关研究

对新红星、金冠等５个品种果实生物学指标在果实成熟和贮藏期变化规律进行了研究，并对其各自在判断果实成熟和确定采收适期中的作用和意义进行了评价。认为果实糖和酸含量、糖酸比例、可溶性固形物、维生素Ｃ等项指标只能指示果实品质的优劣；果肉硬度在果实成熟衰老过程中变化激烈，但进入成熟期有一缓慢变化时间，也降低了其判断成熟的精确性，只可作为参考指标；果实淀粉的消长规律直接反映果实的成熟状态，是果实成熟的重要标志。果实剖面淀粉磺－碘化钾染色面积大小，在一定程度上指示了果实成熟度，不同品种有其特定染色图谱。     

Leatheriness and mealiness of peaches in relation to fruit maturity and storage temperature

Summary

`Huangjin' peaches (Prunus persica Batsch) were harvested at commercial harvest time (commercial) and 20 d before (early) or after (later) commercial harvest. Fruit from each harvest were stored at three temperature regimes (0, 5 and 10°C) at 95% r.h. After four weeks of storage at 0 or 5°C, early harvested fruit developed more leatheriness but less mealiness and later harvested fruit did not develop leatheriness but developed more mealiness comparedwith fruit from commercial harvest. Overall, fruit stored at 5°C developed more mealiness but less leatheriness than fruitat 0°C for the same period of storage. When stored at 10°C for two weeks, after which fruit were senescent, fruit did not develop any leatheriness or mealiness regardless of harvest times. Fruit with leatheriness were firmer (>30 N) thanjuicy or mealy fruit (<10 N) after the same period of cold storage and 4 d at 20°C. Mealy fruit were as soft as juicy fruit. 1-Aminocyclopropane-1-carboxylate oxidase (ACO) activity, 1-aminocyclopropane-1-carboxylic acid (ACC) content, and polygalacturonase (PG) and galactosidase (GAL) activities were lower, and insoluble pectin content was higher in leathery fruit than that in juicy or mealy fruit. ACO, PG and GAL activity, ACC, and insoluble pectin content were similar between mealy and juicy fruit.     

Combinations of GA3 and AVG delay fruit maturation,increase fruit size and improve storage life of `Feicheng' peaches

Summary

Different concentrations of aminoethoxyvinylglycine (AVG) and gibberellic acid (GA₃) and their combinations, applied at two stages of fruit growth, were evaluated for prolonging the marketing season of `Feicheng' peaches. GA<sub>3</sub> applied at the end of pit hardening, or AVG applied two weeks before commercial harvest, inhibited fruit maturation on the tree, delayed harvest and reduced flesh browning after cold storage in a concentration-dependent manner. A synergistic effect was found when both GA<sub>3</sub> and AVG were used, with the combination of 100 or 150.mg l<sup>±1</sup> GA<sub>3</sub>, applied at the end of pit hardening, and 100 mg l<sup>±1</sup> AVG, applied two weeks before harvest giving the best results. These combinations retarded the change in ground colour, loss of firmness, and reduction in acidity by 2±3 weeks. Since harvest was prolonged by 2±3 weeks, soluble solids content (SSC) in fruit increased compared with the control (harvested earlier). Fruit size was significantly greater on treated trees compared with the controls when fruit set was controlled to the same level by hand thinning. After four weeks of storage and 4.d at 208C, 83% of control fruit developed tissue browning, but only 5% of AVG + GA<sub>3</sub>-treated fruit developed browning after six weeks of storage and 4 d at 208C. Thus, the marketing season of `Feicheng' peaches was prolonged by at least four weeks by 100 or 150 mg l^±1 of GA₃ and 100 mg l^±1 of AVG. Fruit treated with 150 mg l^±1 GA₃ plus 100 to 150 mg l^±1 AVG showed similar results but failed to ripen properly after cold storage.     

The inhibition of flower bud differentiation in ‘Crimson Gold’ nectarine with GA3 as an alternative to hand thinning

The reduction of flower bud density by gibberellin sprays, to adjust the cropping level, is a novel approach to fruit thinning of peach and nectarine. A linear reduction in the number of flowers developed per unit of shoot length was found following the spray application of increasing concentrations of GA₃, in the nectarine cultivar ‘Crimson Gold’. These reductions in flower number led to reductions in yield at harvest, and increases in mean fruit weight. Flowering was slightly delayed by the GA₃ treatments, but no differences in ripening were detected at harvest, this depending rather on fruit size. The yield obtained by the application of 200 mg l⁻¹ GA₃ corresponded to that obtained with a very good thinning level, as established by hand thinning. No secondary effects on vegetative growth followed either the application of GA₃ or the reductions in crop load by means of hand thinning. Decreasing crop-loads have resulted in an increase in fruit size and an advance of fruit ripening, measured by greater levels of soluble solids and lower flesh firmness. A good commercial quality fruit size was obtained for crop-loads of 300 fruits per tree or less.     

Flower bud thinning in ‘Rojo Liso’ cactus pear

Summary

The export of cactus pear fruit from Mexico has increased over the last decade, with growing consumer demand for larger and higher quality fruit. Growers are concerned that yields decrease when fruit thinning is used to increase fruit size. Our objective was to assess the effects of flower bud (FB) thinning on the pre-harvest and post-harvest attributes and yields of ‘Rojo Liso’ cactus pear (Opuntia ficus-indica) fruit. The experiments were conducted in 2005 and 2006. The treatments used were: 1) no thinning, considered as the control; 2) thinning every second bud (T1); or 3) thinning two out of every three buds (T2). Marketable fruit (having an equatorial diameter > 5 cm) in the thinned treatments increased compared to the unthinned controls in both seasons. Thinning did not reduce fruit yield. Fruit quality was similar among treatments, both at harvest and after storage, except for the soluble solids concentrations which were higher in both the T1 and T2 treatments in 2005. Fruit weight loss in storage was similar among treatments. Flower bud thinning can therefore be recommended for commercial use.     

Grafting effects on postharvest ripening and quality of 1-methylcyclopropene-treated muskmelon fruit

In addition to managing soil-borne diseases in muskmelon (Cucumis melo L.) production, grafting with resistant rootstocks may impact fruit quality. The ethylene antagonist 1-methylcyclopropene (1-MCP) has been shown to extend shelf life of fresh muskmelon fruit. Postharvest characteristics of 1-MCP-treated melon fruit as affected by grafting, however, have not been well examined. This study was conducted to explore the influence of grafting with different rootstocks on ripening and quality attributes of 1-MCP-treated muskmelon fruit during postharvest storage. Grafted ‘Athena’ muskmelon with two commercial squash interspecific hybrid rootstocks including ‘Strong Tosa’ and ‘Tetsukabuto’ as well as non-grafted and self-grafted ‘Athena’ were grown in replicated field plots at the University of Florida Plant Science Research and Education Unit (Citra, FL, USA) during April–June 2010. Half-slip fruit from two harvests were treated with 1.0 μL L⁻¹ 1-MCP (18 h, 20 °C) and analyzed during storage at 13 °C. For fruit from the 27 May harvest, whole fruit and mesocarp firmness, titratable acidity, soluble solids, and ascorbic acid content were measured, while production of ethylene and CO₂ was determined on fruit from the 29 June harvest. Grafting did not show a significant impact on fruit yield but affected the fruit shelf life significantly. Fruit from non-grafted ‘Athena’ and ‘Athena’ grafted onto ‘Strong Tosa’ demonstrated a shelf life of 31 d for the first harvest and 22 d for the second harvest. Shelf life of fruit from self-grafted ‘Athena’ and ‘Athena’ grafted onto ‘Tetsukabuto’ declined by 6 d and 3 d for the first and second harvest, respectively. Whole fruit firmness decreased by approximately 15.5% on average from 13 to 31 d except day 19 as a result of grafting, but to a lesser extent with ‘Strong Tosa’ rootstock. Mesocarp firmness of grafted melon was reduced by about 30.2% at days 13 and 19 compared to non-grafted ‘Athena’ fruit. In contrast, titratable acidity, soluble solid content, and ascorbic acid concentration were less affected by grafting. All the measurements except for ethylene and CO₂ production declined during storage regardless of the grafting treatment. Compared with ‘Strong Tosa’ rootstock, ‘Tetsukabuto’ resulted in a more rapid ripening under 1-MCP application, as reflected by earlier increase in ethylene production and higher respiratory rate. The study demonstrates that grafting effects on postharvest ripening and quality of ‘Athena’ muskmelon can vary markedly with rootstocks used.     

The effects of storage temperature and fruit size on firmness,extractable juice,woolliness and browning in two nectarine cultivars

Fruit firmness, extractable juice, woolliness and browning of the mesocarp tissue in ‘Independence’ and ‘Flavortop’ nectarines stored at —0.5°, 3°, 5° and 7°C for four weeks were determined during ripening at 15°C. The firmness of both ‘Independence’ and ‘Flavortop’ during ripening decreased as storage temperatures increased. The percentage extractable juice after cold storage and during ripening varied considerably between cultivars and between the storage temperatures. The extractable juice of fruit stored at higher temperatures tended to increase during ripening, whereas fruit stored at lower temperatures tended to decrease first before increasing. At storage temperatures of —0.5° and 3°C both cultivars passed through a stage of woolliness during ripening, while less woolliness occurred after storage at 5° and 7°C. In both cultivars the percentage extractable juice during ripening was higher on average at storage temperatures of 5° and 7°C. Severe browning of mesocarp tissue in both cultivars occurred during ripening after storage at 3°C. The effect of fruit size on changes in firmness, development of woolliness and mesocarp browning in ‘Flavortop’ nectarines stored at — 0.5°C for four weeks and ripened at 15°C was also determined. Larger nectarines lost firmness more rapidly, woolliness occurred sooner and the mesocarp tissue was more prone to browning than smaller fruit during ripening.     

Interaction of Crop Load and Irrigation on Yield,Fruit Size,Color and Stem-end Splitting Ratio of Apple c.v. ‘Gala,Galaxy’

In this study, the interaction between crop load and irrigation level on yield, fruit size, skin color and stem-end splitting fruit ratio in the apple cultivar ‘Gala, Galaxy’ grafted on rootstock M9 were investigated. Six irrigation programs were applied during the whole growth season: deficit irrigation (rates of 0.25 kc, 0.50 kc, 0.75 kc), full irrigation (rate of 1.00 kc), excess irrigation (rate of 1.25 kc) and non-irrigation (rates of 0.00 kc of “Class A” pan evaporation coefficient). Four crop loads in each irrigation application were performed by hand thinning after the June drop as a- a low crop load (3 fruits cm^?2 TCA), b- a medium crop load (5 fruits cm^?2 TCA), c- a heavy crop load (7 fruits cm^?2 TCA), and d- an un-thinned crop load (>?7 fruits cm^?2 TCA). The total tree yield increased with crop load and irrigation levels. Fruit size was significantly increased by the low crop load. Irrigation increased the fruit size compared to non-irrigation treatment. Further 0.75 kc, 1.00 kc and 1.25 kc irrigation treatments significantly increased the fruit length. Irrigation reduced the fruit flesh firmness. While the low crop load increased the skin red color, it decreased the fruit skin brightness. The yellowness of skin decreased with increasing in the irrigation amount. Irrigation reduced the skin brightness and yellowness, but it increased red color. Crop load and irrigation significantly affected the stem-end splitting fruit ratio. While the splitting fruit ratio increased with a decrease in the crop load, it decreased with an increase in irrigation amount, relatively. Consequently, the low and medium crop load treatments would be beneficial to increase the ratio of marketable fruits without any significant losses in yield for ‘Gala’ apple, especially under 0.75 kc deficit irrigation treatment.     

Soil and rootstock influence on fruit quality of plums (Prunus domestica L.)

Soil and rootstock can particularly affect the ‘Rainha Claudia Verde’ (Prunus domestica) fruit quality, mainly its firmness characteristics. To investigate the variation in fruit quality, plums were harvested at commercial maturity from trees grafted on Marianna GF8-1 (Prunus cerasifera × munsoniana) and Marianna GF10-2 (P. cerasifera × munsoniana) rootstocks on two different soils: Haplic Luvisol and Vertic Luvisol. After harvest fruits were stored at 2 °C for 3 weeks. At the harvest day a small group of fruits were analysed without cold storage. During storage fruits were tested for firmness, soluble solids content, titratable acidity and fruit mineral content. Tree vigour was evaluated from trunk cross-sectional areas values.The GF8-1 rootstock promoted the highest vegetative development, comparing to GF10-2. This rootstock promoted the largest fruits size and the higher calcium fruit level. Positive correlations were found between higher concentrations of calcium in the pulp fruits and firmness. Fruits from two different rootstocks showed the same firmness at harvest but during cold storage, fruits from GF10-2 rootstock exhibited the highest firmness pulp values. There weren’t significant differences in fruit nitrogen and potassium levels for any studied factor.At harvest solids soluble content and solids soluble content/titratable acidity ratio weren’t affected by soil type or rootstock. As expected, solids soluble content during cold storage increased and solids soluble content/titratable acidity had a slight increase.GF10-2 revealed to be a good option as a ‘Rainha Claudia Verde’ rootstock for plums growers due to its intermediate-vigour. Also GF10-2 fruits presented better quality during storage comparing with GF8-1.     

疏果处理对硕光杏花器官质量的影响

疏果是改善果实品质的重要技术之一。以鲜食杏品种硕光为研究试材,以不疏果为对照,研究了疏果处理(果间距5cm、10cm和15cm)对翌年杏花器官质量的影响。结果表明:疏果处理可以提高花芽、花瓣和雌蕊的重量,降低雌蕊败育率。     

Effects of different crop loads and thinning times on yield,fruit quality,and return bloom in Malus × domestica Borkh. ‘Elstar’

Summary

‘Elstar’ is the latest-maturing commercial apple cultivar grown in Norway, with high fruit quality when properly managed. In May 2006, an experiment with four different crop loads [2, 4 ,6, or 8 flowers or fruitlets cm^–2 trunk cross-sectional area (TCSA), respectively] was established at two different stages [first bloom (FB), or 20-mm diameter fruitlets] and compared to unthinned control trees. Fruit growth was measured on individual fruit for each treatment throughout the season at weekly intervals. Thinning at FB gave a significantly lower final percentage fruit set than thinning to the same cropping level at the 20-mm fruitlet stage. However, fruit weights and soluble solids contents (SSC) were significantly higher, and the background fruit colour improved when trees were thinned at FB. The final number of fruit at harvest was less than the amount established at FB, or at the 20-mm fruitlet stage. There were significant differences between treatments in final fruit numbers per TCSA, which reflected the different crop loads. Fruit weights and SSC values were highest with the lowest crop load, and decreased with increasing crop loads. There was also a strong crop-load effect on the extent of return bloom per tree in the subsequent year. Trees thinned at FB had significantly more flower clusters than those thinned at the 20-mm fruitlet stage of. Untreated control trees had the lowest number of flower clusters. The amount of return bloom declined with increasing crop load. Second year crop loads and fruit weights were highest when trees were thinned at FB to two or four apples cm^?2 TCSA in the previous year. Trees with the highest crop load had the lowest crop load in the following year. Fruit quality was generally high for all treatments.