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.     

Evaluating the effectiveness of different strategies for calcium application on the accumulation of calcium in apple (Malus × domestica Borkh. ‘Braeburn’) fruit

Summary

Orchards displaying calcium (Ca) deficiency are a common phenomenon worldwide, despite the presence of sufficient Ca in the soil and the plant. A 3-year trial was conducted between the 2007 – 2008 and 2009 – 2010 growing seasons to evaluate the contributions of soil and foliar Ca applications to Ca concentrations in ‘Braeburn’ apple (Malus × domestica Borkh.) fruit. Ca(NO₃)₂ (Calflo; Yara Africa, Fourways North, South Africa) was applied as six separate foliar sprays until run-off. Applications were made at 1-week intervals between approx. 21 – 70 d after full bloom (DAFB) at 6.75 ml l^–1. Soil applications of Ca (Tropicote^TM; International ASA, Oslo, Norway) at 300 kg ha^–1 were applied at fruit set, or after harvest, according to standard practice. Mineral analysis was conducted to assess the soluble Ca concentrations of whole fruit (without pips and stalks), to quantify the contribution of foliar sprays or soil-applied Ca. Fruit Ca concentrations were maintained at satisfactory levels (4.5 mg Ca 100 g^–1 FW) at harvest by applying a series of six foliar sprays early in the season (for all seasons) during the trial period. Fruit Ca concentrations at 80 DAFB were highest in the treatments with foliar applications of Ca. In 2009 – 2010, Ca concentrations in apple fruit were lowest (8.38 mg 100 g^–1 FW) for soil application of Ca at fruit set. Ca applications to soil after harvest in the previous season, and soil applications shortly after fruit set in the current season, did not significantly increase Ca concentrations in current-season fruit, providing soil Ca levels were above the minimum requirement for apple trees. A possible explanation is that apple trees regulate their uptake of Ca through the roots when soil Ca is available in sufficient quantities. This confirms the importance of active root growth for efficient Ca uptake by apple trees when applying Ca to the soil.     

Hormonal control of splitting in ‘Nova’ mandarin fruit

Fruit splitting, a physiological disorder of peel development in citrus, has been studied in terms of peel thickness and puncturing resistance in ‘Nova’ mandarins. Both features are negatively correlated with splitting. A mixture of G A, and 2,4-D reduced significantly the percentage of affected fruits. The best results were obtained with two applications at 60 and 30 d before the anticipated onset of the disorder. Calcium nitrate applications have similar effects, but were ineffective in orchards with a low natural incidence of splitting.     

Determination of optimal harvest boundaries for ‘Ambrosia’ apple fruit using a delta-absorbance meter

In this study, a new chlorophyll measurement tool, the delta absorbance (DA) meter, was used to develop an optimal harvest maturity model for ‘Ambrosia’ apple (Malus × domestica Borkh.) fruit. Fruit from four commercial orchards in the Annapolis Valley, Nova Scotia, Canada, were sampled (25 fruit from three or four trees per location) over nine consecutive weekly harvests during the 2011 and 2012 growing seasons, and 8 weeks in the 2013 season. At each harvest, five fruit from each orchard site had their index of absorbance difference (I_AD) values, firmness, mass, titratable acidity (TA), soluble solids content (SSC), red skin colouration and internal core ethylene concentrations measured. Following approx. 3 months of storage at 3.5°C, 20 fruit from each site were removed and assessed for the incidence of disorders such as senescent breakdown, cortical browning and coreflush. Chlorophyll concentrations in the epidermis were strongly and positively related to I_AD values in the same tissue (P ≤ 0.001), confirming the assumption that chlorophyll was the basis for the DA meter I_AD signal. In addition, I_AD values declined significantly during fruit maturity and were negatively related to harvest week (P ≤ 0.001). The optimum harvest period was identified by aligning all ‘at harvest’ I_AD values, fruit quality measurements, and ‘post-storage’ disorder data with the corresponding harvest week. I_AD values associated with harvests having the highest commercial fruit quality then delineated the optimal harvest boundaries. The upper boundary I_AD value of 0.47 was defined as ‘when to begin harvest’, while the lower boundary I_AD value of 0.28 was considered to be ‘when to end harvest’ for long-term storage. The use of a DA meter and its I_AD value to define the optimal harvest boundaries may be applicable to all commercial apple cultivars, but should be developed for each cultivar and growing region.     

Harvest parameters to improve the storability of high quality ‘Reinette du Canada’ apple

Summary

‘Reinette du Canada’ apple (Malus domestica Borkh.), which has been declared a Protected Designation of Origin (PDO) product throughout the European Community, is severely affected by bitter pit during storage, but increasing demand for organic produce requires chemical post-harvest treatments to be replaced with organic practices. The objective of this work was to determine the optimum stage of fruit maturity to improve the storability of high quality ‘Reinette du Canada’ apple during storage without applying post-harvest treatments. Seasonal conditions influenced fruit quality and the occurrence of storage disorders in ‘Reinette du Canada’. Harvest maturity also influenced the quality of ‘Reinette du Canada’ apple during storage, with later harvests reducing the development of bitter pit and increasing the soluble solids content:titratable acidity (SSC:TA) ratio. This study suggests that the SSC:TA ratio was a useful parameter for determining the optimum harvest maturity for high acidity, ‘Reinette du Canada’ apple. High quality fruit were obtained after long-term storage when the SSC:TA ratio exceeded 11.0, and fruit firmness at harvest exceeded 90 N. If these thresholds were not achieved, the quality of harvested ‘Reinette du Canada’ apples may not be sufficient to market fruit with the PDO designation. The results of our study also suggested that skin hue angle (hº) measurements may provide a quick and useful index that could replace fruit firmness measurements in the future.     

Response of ‘Early Imperial’ Mandarins to Selective Harvesting

All cv Early Imperial mandarin fruits with circumferences 14 cm or more were removed in the first week of May or in July and the remaining fruits as well as those from the controls were picked in the last week of August. Increases in fruit circumference and in fruit weight were recorded only on the trees selectively picked in May, suggesting a minimum time requirement for sizing after removing about 25% to 40% of the fruit. Changes in palatability, colour, puffiness and dryness with time indicated that selective harvesting should not be practised beyond late August to avoid dryness and puffiness.     

A comparison of different thinning products applied to the apple variety ‘Elstar Elshof’ in the Lower Elbe region

6-Benzyladenine (BA) showed only a slight thinning effect which was probably correlated with low temperatures during application. It is concluded that under the current climate of the Lower Elbe region temperature is a more important factor than fruit size for determining the time-point of BA application. Ethephon at 300?ppm produced a stronger effect, even if this was still insufficient in the present case. Higher concentrations (450–600?ppm) are required for strongly flowering ‘Elstar’ plantations older than 4?years, but this invokes the risk of excessive thinning. Therefore, the application of Ethephon requires a high degree of experience on part of the fruit farmer. Metamitron, applied once at 350?ppm, showed similar effects to Ethephon. An enhanced effect might have been obtainable if a second treatment had been applied some 10?days later. No phytotoxic damage was observed. Metamitron would be an interesting fruit thinning agent and should be considered for registration in Germany. Naphthalene acetic acid (NAA) and NAA + BA gave the best results in the experiment for 2006?described here. It is not yet clear whether the degree of flowering for 2007 will be influenced in a similarly positive manner as for Ethephon. Since NAA and Metamitron have not been registered for Germany, their practical use cannot be recommended.     

Effect of calcium supply on the physiology of fruit tissue in ‘Andesu’ netted melon

Summary

Fruit development and physiological traits were evaluated in ‘Andesu’ netted melon plants grown with and without calcium. Calcium exclusion accelerated softening, alcoholic fermentation and ethylene evolution of fruit compared with those supplied with calcium, but the opposite trend occurred with sucrose accumulation. A significant difference of calcium concentrations in the fruit between treatments was observed at the developing stage of the fruit (P<0.05), but the difference became smaller as fruit matured. In the mesocarp tissue from the basal hemisphere, calcium concentrations in the NaCl soluble fraction at ripe fruit stage differed significantly (P<0.05) between calcium treatments but no significant difference was detected in the inner mesocarp of the distal hemisphere. Calcium exclusion did not lead to the development of water-soaked symptoms in the mesocarp tissue of ripe fruit. Uronic acid concentrations in ionically bound pectin fraction did not differ between calcium treatments throughout fruit development. In covalently-bound pectin fraction, however, uronic acid concentration of ripe fruit was significantly lower in calcium-excluded plants than in calcium-supplied plants (P<0.05). Our results suggest that: first, accelerated fruit softening under calcium deficient conditions might result from promoted ethylene evolution rather than from the shortage of ionically-bound calcium in cell walls, second, calcium deficient condition does not necessarily lead to water-soaked symptoms in tissue of ‘Andesu’ melon fruit.     

Seasonal variation in the onset and duration of flower development in ‘Royal Gala’ apple buds

Summary

The formation of bud scales, transition leaves, true leaves, bracts and flower primordia were observed in buds removed from non-flowering sites on one year old shoots of apple ‘Royal Gala’. Buds were sampled from trees in Hawke's Bay, New Zealand (latitude 398S) during six successive seasons. The onset of flower development varied between seasons from 72 to 99.d after full bloom. Floral development was poorly synchronized within the populations of sampled buds, lasting 22 to 50.d. Differences in the onset and duration of flower development could not be related to seasonal differences in heat accumulation from full bloom. There was significant variation between seasons in the minimum number of appendages observed within buds that exhibited doming, which indicates floral development. In the 1998/99 season, doming was observed in buds that had only 15.7 appendages, whereas in the 1999/2000 season the minimum number of appendages within a bud that had initiated flowers was 17.5. When the data from all seasons were considered, the rate of appendage formation within developing buds was not consistently related to heat accumulation.     

Foliar application of calcium plus boron reduces the incidence of sunburn in ‘Golden Delicious’ apple

Summary

Losses of apple fruit due to sunburn damage under South African climatic conditions can reach up to 40% per annum for specific cultivars in certain years. Various approaches to reduce the incidence and severity of sunburn resulted in temporary effects but, at present, no single remedy is available to provide a significant and consistent reduction in sunburn damage on a commercial scale. ‘Golden Delicious’ apple trees that received both calcium (Ca) and boron (B) as foliar applications on a weekly basis, when applied from approx. 21 – 70 d after full bloom (DAFB), showed significantly less sunburn in two consecutive seasons (P = 0.0500 and P = 0.0247 respectively) than untreated control fruit, or treatments based on Ca alone. The minerals were applied as supplements of sugar-alcohol complexed with Ca and B, trading as Manni-Plex^® Ca [10% (w/w) Ca] and Manni-Plex^® B [3.3% (w/w) B], respectively. The mode of action by which the incidence of sunburn was reduced using combined sprays of Manni-Plex^® Ca plus Manni-Plex^® B remains to be elucidated.     

Analysis of S-alleles by PCR for determination of compatibility in the ‘Red Delicious’ apple orchard

Summary

In a previous study, the apple ‘Jonathan’ was shown to be semi-compatible with the ‘Topred’ sport of ‘Red Delicious’, the main cultivar in Israel. This incompatibility led to reduced pollination potency, explaining the low yield obtained from ‘Topred’ rows adjacent to ‘Jonathan’. Hence, the importance of identifying the level of compatibility for all ‘Topred’ pollinators became apparent. By analysing S-allele by PCR with primers for the various S-alleles of the cultivars in the ‘Topred’ orchard, including S10 and S28, which were cloned in this study, it was evident that apart from ‘Jonathan’, the common pollinators for ‘Topred’ are fully compatible with it. The ability to identify all S-alleles in the ‘Topred’ orchard was also utilized to resolve the observation that, although ‘Topred’ is considered self-incompatible, self-pollinated, net-caged, ‘Topred’ flowers set some fruit. Applying PCR-analysis of S-alleles to the progeny of the suspected self-pollinated ‘Topred’ fruit revealed that the fruit-set was the outcome of cross-pollination, perhaps the consequence of fertilization by wind carried pollen. Hence, the notion that ‘Topred’ is totally self-incompatible was confirmed and the efficiency of progeny PCR S-allele analysis for the determination of the pollen donor was exhibited.     

Prohexadione-calcium effects on the quality of ‘Royal Gala’ apple fruits

Summary

To study the effects of prohexadione-calcium (Pro-Ca) on fruit quality, an experiment was performed in 2002 in which trees were treated with two different concentrations of Pro-Ca and left with different crop-loads. Increasing levels of thinning resulted in smaller yields, but greater fruit sizes, which followed a curvilinear pattern when plotted against crop-load. The soluble solids content and titratable acidity of fruits decreased linearly with increasing crop-load. Fruit skin chromaticity values also changed. Luminescence increased, while a* values decreased linearly with increasing crop-load, indicating more reddish and darker coloured fruits on trees subjected to very heavy thinning. In addition, the concentrations of soluble sugars in fruits changed with the level of cropping; fructose and glucose concentrations increased with crop-load, while sorbitol and sucrose decreased. The application of Pro-Ca shortly after full-bloom inhibited shoot elongation growth, but did not result in changes in yield or in any of the fruit quality parameters analysed.     

The influence of endothal and 6-benzyladenine on crop load and fruit quality of red ‘Delicious’ apple

Summary

Trial work over a two year period examined the aquatic herbicide endothal as a blossom thinner in conjunction with 6-benzyladenine (CyLex?) as a post-bloom thinner. The aim was to develop an effective thinning programme using endothal and CyLex?, to examine any interactions between the two chemicals, and to assess the impact of endothal on fruit quality. Time of application of endothal was shown to be critical in achieving a satisfactory level of thinning. Multiple applications of lower chemical rates were also successful, and may have potential to provide an effective programme for cultivars with long flowering periods, which are traditionally most difficult to thin. Addition of a surfactant to the spray mix significantly increased the thinning effect of endothal, resulting in severe over-thinning. This work has demonstrated that endothal is an effective thinner of red ‘Delicious’ apples. It is most effective when applied twice during the blossom period, the first application at 20% bloom and the second at 80% bloom. There is no advantage in increasing the concentration above 1.0 cm³ dm^-3 (v/v). Endothal can also be effectively combined in a programme with the post-bloom thinner CyLex? applied at 150 mg l”¹ at a spray volume of 12001 ha^-1. Addition of CyLex? to the spray programme has the added benefits of increasing fruit weight and size. Fruit sugar content and firmness were both increased by application of endothal. The greater the number of applications the higher the firmness and sugar content of the fruit. Both these findings are additional benefits to the thinning effect. Both pip number and fruit length/diameter ratio were slightly reduced by endothal. Cylex and some endothal treatments increased the incidence of fruit russet.     

Aroma volatiles emission in relation to chilling injury in ‘Kensington Pride’ mango fruit

Summary

Mature green mango fruit (Mangifera indica L. ‘Kensington Pride’) were stored at 0, 5, 10, 15 or 20°C for 1, 3, 7, 14, 21 or 28 d to induce different levels of chilling injury (CI) and to elucidate its relationship with aroma volatile production. The fruit were removed from storage and allowed to ripen at 22 ± 1°C and CI index was assessed on fully ripe fruit. Aroma volatile compounds were estimated from the pulp of fully ripe fruit. CI index significantly increased as the storage temperature was lowered and the storage period was extended, particularly in the fruit stored at 0, 5 or 10°C. CI symptoms did not develop on fruit stored at 15 or 20°C. Fifty-six aroma volatile compounds were identified from mango fruit pulp using headspace solid phase microextraction (SPME) technique with gas chromatography (GC-FID) and GC combined with mass spectrometry (GC-MS). Among the 56 aroma volatile compounds, 25 were quantified using GC, which included monoterpenes (±-pinene, ²-pinene, myrcene, 2-carene, ±-phellandrene, 3-carene, ±-terpinene, limonene, ocimine, ³-terpinene, ±-terpinolene, and a-terpineol), sesquiterpenes (±-copaene, ±-gurjunene, trans-carophyllene, aromadendrane, ±-humulene, alloaromadendrane, ³-gurjunene, and ledene), hydrocarbon (p-cymene), esters (methyl octanoate and ethyl caprylate), aldehyde (decanal), and norisoprenoid (²-ionone). A significant reduction in total aroma volatiles, monoterpenes, sesquiterpenes, hydrocarbon, esters, aldehyde, and norisoprenoid production were observed in fruit stored at 0, 5, 10 or 15°C compared with fruit stored at 20°C. The degree of reduction in aroma volatile compounds depended on the severity of CI, induced with different storage temperatures and storage periods. In conclusion lower temperature storage induced CI in mango fruit and adversely affected the aroma volatiles production.     

Determining the probability of bitter pit in ‘Golden Delicious’ apples through the post-harvest mineral content of individual fruit

Summary

Bitter pit fruit in commercial consignments of apples still poses an economic threat to exporters from South Africa. Mineral analysis of fruit has been used with variable success to predict bitter pit prior to harvest. The possibility of increasing the accuracy of existing predictive models by using analysis of individual fruit rather than pooled samples was investigated. By improving the normality of the distributions of the different minerals and decreasing the overlap between pitted and non-pitted fruit classes, we attempted to improve the reliability of predictions based on variable threshold values. Even though our model produced a correct classification of 85% for non-pitted fruit which can be useful, this was still below the required tolerance expected on the market which, at present, is less than 2% bitter pit in an overseas consignment. The classification for pitted fruit, 63%, was not satisfactory.     

Response of ‘Comice’ pear trees to a postharvest urea spray

A single postharvest urea spray at 5 and 10% increased nitrogen (N) content in one year old bark and wood and in the flower buds and blossoms in 1987. In 1988, there was also an increase in N in one year old bark and wood but not in the N content of flower buds and blossoms. Fruit set was not significantly increased in either year. Control trees were much taller in N in 1988 than they were in 1987 since additional soil N was applied. Urea labelled with 15N was applied to branches and individual spurs immediately after harvest. When the l5N-urea was applied to branches, the next season’s flower buds had 12% of their N derived from the fertilizer (NFF), but when urea was applied to individual spurs only 8% NFF was detected. Remobilization of labelled N from treated to adjacent spurs resulted in less NFF than would occur if all spurs on the same branch received labelled N. Flower clusters distal and basal to the spurs treated with labelled l5N showed considerable amounts (>60% of sprayed spur) of N from the labelled spray. However, harvest analysis of adjacent and distant spur leaves and fruits from treated spurs and branches revealed that urea was only locally mobilized in the tree. Nitrogen status can be altered with postharvest urea sprays but the response varies with the N status of the tree. Postharvest soil application of labelled N showed N movement into blossoms but not in the flower buds.     

Carbohydrate changes in flowers,leaves, shoots and spurs of ‘Cox’s Orange Pippin’ apple during flowering and fruit setting periods

Summary

Changes of carbohydrate concentrations in different parts of the flower and the surrounding tissues (leaves, spurs and shoots) were measured in apple (Malus pumila) in 1987 and 1988, during the periods of flowering and fruit setting, to investigate their importance for fruit setting. HPLC was used for soluble sugar and sorbitol analysis. Starch was hydrolysed to glucose enzymatically and glucose concentration was determined colorometrically to estimate starch concentrations. Soluble sugars plus sorbitol (the soluble pool) increased rapidly in all parts of the flower from bud burst until full bloom. In contrast, in the same period, starch concentrations decreased rapidly and reached about zero at full bloom in the storage organs (shoots and spurs), indicating starch conversion to sugars and their movement to the growing flowers. Sorbitol was the most abundant carbohydrate in all apple tissue measured, with the exception of sepals, in which glucose concentration was the highest from full bloom onwards. Sepals had much higher glucose and fructose concentrations than leaf laminae but much lower sorbitol concentrations. Although dry weight, soluble pool and starch concentrations and total soluble pool content increased in the receptacle after petal fall, sucrose concentrations and total sucrose content dramatically decreased. These results suggest a preferential mobilization and utilization of sucrose rather than sorbitol during the fruit setting period and probably an important role of sucrose metabolism in fruit setting.     

Effect of agar,galactomannan and indole-butyric acid on in vitro rooting of the pear cultivar ‘Durondeau’ and apple rootstock cultivar ‘Marubakaido’

Summary

The influence of partial substitution of agar by galactomannans in culture media supplemented with different concentrations of indole-3-butyric acid (IBA) was studied on in vitro rooting of pear (Pyrus communis L.) cultivar ‘Durondeau’ and apple rootstock (Malus prunifolia Borkh.) cultivar ‘Marubakaido’. The galactomannans applied were obtained from Cassia fastuosa (cassia) and Cyamopsis tetragonolobus (guar gum) seeds. The results obtained with mixtures of agar and galactomannan (3 g l^–1 each) were compared with those from media solidified with a standard concentration of agar (6 g l^–1). The rooting of pear shoots was enhanced significantly in the presence of a mixture of agar plus cassia galactomannan compared to medium solidified with agar only. The modified media promoted a higher number of roots than the control, and increased the percentage of rooted shoots. A maximum of 84.8% rooting was obtained on half-strength MS medium (¹?2MS) supplemented with 0.49 µM IBA and solidified with a blend of agar plus cassia galactomannan. For the apple rootstock, only the number of roots per shoot was influenced significantly by the addition of galactomannan to the rooting medium. The highest number of roots per shoot was 16.67 on ¹?2MS medium gelled with a mixture of agar plus guar galactomannan supplemented with 4.90 µM IBA. The behaviour of the agar-galactomannan gel and the possibility of reduced costs when compared with systems containing only agar, suggest new biological and commercial applications for galactomannans.     

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

Summary

Shade 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.     

The effect of gibberellins and cytokinins on fruit development of Bramley’s Seedling apple

Two applications of a 1 : 1 mixture of gibberellins A₄ and A₇ to either frost damaged or artificially decapitated Bramley's Seedling apple flowers resulted in increased fruit set and yield. It also increased the crop in an orchard without pollinators. Gibberellic acid was not effective. The addition of cytokinins had no beneficial effects and caused malformation.