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Bitter pit is a physiological disorder that can develop during storage and result in major economic losses of susceptible apple cultivars such as ‘Honeycrisp’. Prediction methods to determine the risk of disorder development have focused primarily on mineral composition of the fruit, but there has also been interest in non-mineral based methods. In this study, we have compared non-mineral methods with mineral analyses for bitter pit prediction. Fruit of ‘Honeycrisp’ were harvested three weeks before anticipated commercial harvest and at commercial harvest. Mineral contents in peel from the calyx-end were measured in fruit at both harvest times. In year 1, fruit were kept at 20 °C (passive method), dipped in 2000 mg L−1 2-chloroethylphosphonic acid (ethylene method) or 0.8 M MgCl2 (Mg method). Treated fruit were then kept at 20 °C for three weeks. At commercial harvest, fruit were stored at 0.5 or 3 °C with and without 1 week of conditioning at 10 °C. The Mg method showed toxicity on the fruit, which was hard to distinguish from bitter pit. Therefore, in year 2, only the passive and ethylene methods were used, and fruit from the commercial harvest were stored at 3 °C with or without conditioning. In year 3, only the passive method was used because of its simplicity and lack of registration of ethephon for this purpose. Fruit from the commercial harvest of 38 orchards in three growing regions were stored at 3 °C after conditioning. Fruit were stored for two months in year 1 and four months in years 2 and 3, and assessed after 4 d at 20 °C. Multivariate analysis shows that the passive and ethylene methods for fruit harvested three weeks before the anticipated harvest had higher or similar correlations with the actual bitter pit after cold storage than those from minerals. Although actual bitter pit incidence was higher than that predicted from the passive method, the method results in predictions that are similar to mineral-based predictions, and also is more straightforward for commercial application.

Honeycrisp apple trees are highly prone to biennial bearing and bitter pit (BP). This 3-y study tested the hypothesis that tank mix sprays of ethephon (ETH), naphthaleneacetic acid (NAA), and 1-aminocyclopropane carboxylic acid (ACC) combined with calcium chloride (CaCl2) can mitigate these production problems. Mature ‘Honeycrisp’ were treated with either three of six applications of 150 mg.L-1 ETH, 5 mg.L-1 NAA or two of five applications of 150 mg.L-1 ACC, all tank-mixed with and without CaCl2 and applied at 10-d intervals starting 21–26 June over three growing seasons. Fruit cortical tissue nutrient concentrations were influenced by applications of CaCl2, ETH, NAA, and ACC. In one year, Ca concentrations were significantly higher in fruit from trees treated with six sprays of ETH or NAA with CaCl2 compared with the untreated control. Compared with untreated trees, fruit Ca concentrations were 115% and 148% higher with three and six applications, respectively. Applications of CaCl2 significantly reduced the incidence and severity of BP post-harvest in two of three years when fruit tissue Ca levels were low. ETH alone also increased the incidence and severity of BP two-fold compared with the control, while early season sprays of NAA reduced BP incidence and severity compared with the untreated control. High and similar levels of BP incidence and severity were observed when six sprays of NAA were applied with or without Ca. Fruit tissue K levels were generally reduced with the addition of CaCl2, and within 1 year, K levels were higher in fruit treated with ACC. Fruit Mg concentrations generally decreased with the addition of Ca or NAA. Six applications of ACC resulted in a 30-fold increase in fruit Mg concentrations compared to the untreated control. Tank mixing CaCl2 with the flower-promoting bio-regulators ETH and NAA proved to effectively reduce BP and increase fruit tissue Ca levels. This approach would offer cost savings when repeat sprays of each are required on a bi-weekly basis.

The potential of dynamic controlled atmospheres (DCA) as a non-chemical treatment for maintaining the postharvest quality of apples during long-term cold storage has been an interest of researchers for decades. This article reviews the recent developments in DCA technology for storage of apples. The effects of DCA on physiological disorders, physico-chemical and sensory quality are discussed. Moreover, negative effects associated with DCA technology are also discussed. The study has shown that DCA maintains apple postharvest quality by reducing respiration rate and ethylene production. Ethylene-mediated physiological disorders such as superficial scald are completely suppressed by DCA storage. However, the effect of DCA on bitter pit incidence needs further investigation. The review also showed that fruit firmness and colour retention is considerable high in DCA stored apples. Although DCA maintains both the physico-chemical and organoleptic quality of apples, the high risk of CO2 and low O2 injury in DCA stored fruit remains a concern. Further research is required to refine and improve the DCA technology in order to minimize the risk of CO2 and low O2 injury during longterm storage.

Susceptibility of apple fruit to physiological storage disorders is affected by both pre- and postharvest factors that influence their ethylene production. In this study, the inhibitor of ethylene perception, 1-methycyclopropene (1-MCP), applied before and after harvest, has been used to investigate the interactions between ethylene and development of physiological disorders in ‘Honeycrisp’ apples during storage. Preharvest 1-MCP (Harvista™) was applied to trees, either 2 weeks (early), 1 week (late), at 1 and 2 weeks (repeated), or at double rate 1 week, before first commercial harvest. Fruit were then untreated or treated with postharvest 1-MCP (SmartFresh®) and stored at 0.5 °C, or conditioned at 10 °C for 7 d and then stored at 3 °C (C + 3 °C), for 20 weeks. Fruit quality and physiological disorders were assessed after 4 d at 20 °C. Fruit from all preharvest 1-MCP treatments had lower internal ethylene concentrations (IECs) and were greener as indicated by higher IAD values compared with untreated controls, while effects on starch pattern indices (SPI) were inconsistent. After storage, preharvest 1-MCP -treated fruit were firmer than untreated fruit, but effects of the different application timings were inconsistent. Effects of postharvest 1-MCP on IEC and IAD values were greater at 0.5 °C than at C + 3 °C. High incidences of core browning and vascular browning developed during storage, especially in the preharvest 1-MCP-treated fruit. Soft scald was reduced by preharvest 1-MCP treatments compared with control. In the C + 3 °C storage treatment, preharvest 1-MCP-treated fruit had a higher bitter pit incidence than in control fruit, but less skin wrinkling and senescent breakdown. Postharvest 1-MCP treatment of preharvest 1-MCP fruit slightly decreased bitter pit incidence while greatly increasing that of core browning and leather blotch, and sometimes flesh browning and carbon dioxide injury. This study shows that pre- and postharvest inhibition of ethylene perception by 1-MCP can have marked effects on storage disorders that are affected by fruit maturity and storage temperatures.

γ-Aminobutyric acid (GABA) can accumulate in apple fruit in response to stress, but little is known about the responses of fruit to GABA treatments. The hypothesis that GABA would inhibit physiological disorder development in ‘Honeycrisp’ apples has been tested in a three-year study. In 2015, ‘Honeycrisp’ apple trees were sprayed with 40 mM GABA 2 and 4 weeks before harvest, and harvested fruit stored at 0.5 °C, a chilling injury-inducing temperature, or 3 °C, for 4 months. In 2016, the same GABA concentration was sprayed on trees at 1 and 2 weeks before harvest and fruit stored at 0.5 °C for 5 months. In the 2017 season, trees were sprayed with 40 mM GABA and 0.12% CaCl2, either alone or in combination, at 1, 2, and 3 weeks before harvest. Postharvest treatments were also applied by dipping fruit in 100 mM GABA and/or 2% CaCl2 at harvest. Fruit were stored in air at 3 °C after 1 week of conditioning at 10 °C, or at 0.5 °C continuously for 5 months. In the first two years, GABA field treatments had little effect on harvest indices, but inhibited soft scald development depending on spray timing. In year 3, GABA provided no benefit, either alone or in combination with CaCl2. Bitter pit incidence was increased by the GABA/CaCl2 combination in fruit from one orchard block, but at times decreased in fruit from a second orchard block. Treatment of fruit by dipping with GABA after harvest decreased soft scald, bitter pit or senescent breakdown incidence in one orchard block, and in combination with CaCl2 inhibited bitter pit to the same extent as CaCl2 alone. Further research is warranted to better understand the effects of GABA on apple fruit metabolism.

Calcium (Ca) sprays and Ca applications to soil throughout the growing season or Ca solution dips at post-harvest are widespread practices to supply Ca and decrease bitter pit in apples. However, published results conflict, and there is no information about the effectiveness of combining all these treatments. In the present study, the following treatments were assessed during four growing seasons: early-season (April) Ca soil applications applied 4 times, mid-season (May) CaCl2 sprays applied 7 or 13 times, late-season (June) CaCl2 sprays applied 7 times, and the combination of late-season sprays and soil applications. In addition, post-harvest dips were evaluated in the latter two growing seasons. Notably high bitter pit incidences were monitored for the first and fourth year of study (>20%), while the second and third year were almost without incidence. Post-harvest dips mitigated bitter pit incidence to a greater extent than pre-harvest treatments, and the sprays mitigated bitter pit to a greater extent than Ca soil applications. The combination of sprays and soil applications did not improve the results relative to Ca sprays alone. No detectable advantage for starting spray programmes earlier than June was observed. Our results showed a trend towards reduced bitter pit with an increasing number of CaCl2 sprays, but this was not clearly an effect of maximizing fruit Ca. Finally, applying 13 CaCl2 sprays in combination with a Ca solution dip at post-harvest appeared to be the most effective practice for minimizing the risk of bitter pit development. This work was partially supported by AECID Project A/021228/08 and by INIA Project RTA 2009-00095, and the ‘CERCA Programme/Generalitat de Catalunya’.

Bitter pit is an economically important physiological disorder in apples resulting in serious economic losses. Current visual assessment techniques are not completely useful in evaluating the extent of bitter pit development as they are limited to external symptoms. An X-ray computer tomography (CT) based imaging and associated image processing algorithm was used to assess the number of bitter pits inside the fruit and on the surface of apples. Samples of 40 healthy and 40 bitter pit affected ‘Honeycrisp’ apples were selected from two different field sites, and scanned with CT equipment on 0, 21 and 63 days after harvest. The results showed that the average number of bitter pits increased both on the surface and inside the fruits with increasing storage period. An average of 42–66% pits was present inside the apple fruits in bitter pit-affected apples. In addition, most of the newly developed bitter pits in healthy apples appeared within the fruit. Therefore, the usefulness of X-ray CT imaging as an effective phenotyping tool in identifying internal bitter pit and on the surface in the automated manner was demonstrated in this study.

Bitter pit (BP) is a physiological disorder that develops in apples, mainly during storage. This study sought to develop NIR spectral models for prediction of future BP incidence and severity in ‘Fuji’ apples using spectral data collected at harvest and during storage. Partial Least Square classification models obtained from spectra reflectance between 950 and 1200 nm were compared, starting at harvest, at 10 days postharvest and every 20 days thereafter over 110 days at 0 °C in relation to BP severity (number of pits per fruit) after 150 days at 0 °C. The models used data from a total of 3000 fruit, collected over two seasons (2018 and 2019) from two orchards. All models were evaluated for Accuracy, Sensitivity, Specificity, Positive Predicted Value (PPV) and Negative Predicted Value (NPV). In the validation dataset, Accuracy, Specificity and NPV values varied between 60 and 80 % and were independent of the time of evaluation during storage. Sensitivity and PPV values did not exceed 60 % in the same dataset. Here, BP incidences in fruit with severities of

Bitter pit (BP) is a physiological disorder of calcium deficiency in apple fruit and has not been fully characterized. The Ca2+/H+ exchanger (CAX) is a kind of Ca2+ transport protein. In this study, we analysed mineral contents in different parts of fruit, the expression levels of genes related to Ca transport and the functional roles of MdCAXs. The results showed lower water-soluble Ca content and significantly higher ratios of water-soluble P/Ca and (K + Mg)/Ca in the calyx-end flesh of BP and normal fruit than the peduncle-end flesh of them. The expression level of MdCAX11 increased as the severity of BP increased, and the expression profile was negatively correlated with the water-soluble Ca content. Yeast growth assays showed that both MdCAX11 and MdCAX5 have the function of transporting Ca to vacuoles. Subcellular localization analysis showed that MdCAX11-GFP and MdCAX5-GFP were colocalized on the vacuole membrane with a tonoplast marker. Taken together, the results of this study indicate that high expression levels of MdCAX11 and MdCAX5 may cause an influx of Ca from the cytosol into vacuoles, which may be related to the occurrence of BP.

‘Honeycrisp’ is a popular apple variety among consumers due to its desirable flavour and characteristic texture. However, this variety is highly prone to pre-harvest fruit drop, bitter pit and decline in quality during long-term storage. This research investigated the effects of hexanal as a formulation (named by us as Enhanced Freshness Formulation -EFF) on fruit retention and post-harvest shelf-life in ‘Honeycrisp’ apples. Hexanal is a known inhibitor of phospholipase D (PLD). Our results indicated that hexanal application reduced PLD enzyme activity from 30 days post-harvest to the end of the storage period compared to the other treatments. Ethylene production was reduced with hexanal treatment from 0 to 90 days post-harvest. An increase in total soluble solids and a decrease in physiological loss in weight was observed with hexanal application. A significantly lower occurrence of progression and severity of bitter pit was observed, while incidence of bitter was reduced by 70 %. Further electron micrographs revealed that hexanal treated apples had higher structural integrity overall. Our results reveal that application of hexanal can reduce bitter pit incidence in Honeycrisp apples, while increasing the post-harvets storage.

Bitter pit is a physiological disorder that is defined as brown, corky and roundish lesions, which can develop in apples before and after harvest. This disorder greatly reduces the product utilization value of the fruit, and can result in several million dollar economic loss to the apple industry. Computed Tomography (CT) imaging is a non-destructive and rapid sensing technique that can be applied to packaged apples. In this study, healthy and bitter pit Honeycrisp apples were harvested from two field sites and stored for 63 days. CT images of the sampled apples were collected on 0, 7, 14, 21, 35 and 63 days after harvest. Images were analyzed to estimate the total pit area in each of the individual apples and were related to pit incidence and progression in different stages of storage. Results showed pit development during the storage period in bitter pitted apples. The rate of progression differed in samples collected from different field sites. Further analysis for pit distribution along each of the bitter pit affected apples showed 54% of pits located at the calyx-end of apples in comparison with middle and stem-end. Classification of healthy and bitter pitted apples using logistic regression based method resulted in false negative of 7–21%.

It is recognized that 1-methylcyclopropene (1-MCP) is able to influence fruit ripening, reduce superficial scald and improve post-storage quality in apples. However, 1-MCP may also increase disorders as bitter pit and diffuse skin browning. The objective of this work was to investigate the effect of 1-MCP (625 nL L −1 ) and 3 different maturity stages (early, middle and late harvest date) on the incidence and development of physiological disorders and ripening delay during storage at 0.5 °C and subsequent shelf-life at room temperature ≈ 22 °C, in ‘Golden Delicious’ apples. Fruit were collected in 6 orchards at a weekly interval, and half were treated with 1-MCP after 3 d cold storage, and the other half left as control. Quality parameters were evaluated at harvest, after 1-MCP treatment and after 6 months storage as well as after 7 d shelf-life. 1-MCP treatment of ‘Golden Delicious’ was effective for slowing softening, reduce electrolyte leakage and color changes associated with ripening (lightness and hue parameters), did not affect soluble solids content and had no clear effect on fruit phenols and antioxidant activity. 1-MCP inhibited superficial scald and significantly reduced rot; however, this treatment enhanced the development of bitter pit in some orchards. Harvest date did not influence scald, bitter pit and firmness but decreased weight loss, total phenols, soluble solid content and antioxidant activity from 2nd to 3rd harvest. The application of 1-MCP, 3 d after cold storage, to ‘Golden Delicious’ apples, reduced ripening and superficial scald, did not induce diffuse skin browning, but increased bitter pit incidence.

We measured mineral nutrient concentrations in leaves, fruit flesh and fruit peel from field grown apple trees grown on a genetically diverse group of rootstocks from year 5 through year 8 of planting (2014–2017) and identified relationships between nutrients in leaves and fruit of ‘Honeycrisp’ apple. We also evaluated the constancy of rootstock influence on scion nutrient profiles over the four years. Boron concentration in both leaf and fruit was consistent in different seasons, with rootstocks M.9 (several clones), B.9, M.26EMLA, PiAu51-11 and B.71-7-22 resulting in consistently low boron levels, while G.935, CG.2034, CG.4004, G.222 and CG.5087 provided consistently high boron levels. Unlike boron, calcium concentration in scion tissues was somewhat variable in different seasons suggesting a role for climate and perhaps management factors in the rootstock induced absorption and translocation of calcium. We identified a group of rootstocks that yielded high calcium levels in scion tissues (G.214, B.10, G.41, B.9, G.935, G.11, CG.4003) while another group yielded low calcium levels (M.26, M.9-T337, G.202, CG.4004, G.814). We also identified a group of rootstocks that induced low potassium values in scion tissues (CG.4003, G.935, G.222, and G.202), whereas B.70-20-21, B.67-5-32, B.70-20-20 yielded consistently higher values. Rootstock B.10 and CG.2034 induced consistently higher potassium values in fruit tissues. The ratio of K/Ca in leaves and fruit was the best predictor of bitter pit in ‘Honeycrisp’ apples, suggesting that rootstock induced levels for both nutrients play a role in this disorder and that the addition of potassium fertilizers on potassium-efficient rootstocks might increase the susceptibility to bitter pit. Rootstocks CG.4003, B.10, G.41 N, and G.214 seemed to produce fruit with lower levels of bitter pit. Our data indicates that some rootstocks are more efficient at absorbing nutrients than others, which implies that fertilizer recommendations developed using one rootstock, such as M.26 or M.9, might be too high for other rootstocks which are more efficient and could thus be causing tree and fruit physiological disorders. Newer rootstocks might be already supplying the needed amounts of minerals to scion tissues. info:eu-repo/semantics/acceptedVersion

‘Honeycrisp’ apple fruit are highly susceptible to development of soft scald and bitter pit during storage. However, the commercial postharvest treatment of conditioning fruit at 10 °C for 7 d before storage at 3 °C to reduce soft scald development can increase bitter pit incidence. Prediction of these physiological disorders would enable storage operators to modify management techniques to reduce fruit losses due to both disorders. To develop prediction tools, harvest indices and mineral concentrations of fruit were analyzed from orchard blocks in Pennsylvania (PA) for three years, the Hudson Valley region (HV) for four years, the Champlain region for two years, and Western New York (WNY) for five years. Fruit were stored at 3 °C, without or with conditioning, and stored for 2 - 5 months in 2013- 2017. Fruit were also stored at 0.5 °C without or with conditioning in 2013, 2015, 2016. Multivariate analysis described significant relationships that were different for unconditioned and conditioned fruit. In unconditioned fruit, bitter pit incidence was negatively correlated with increasing internal ethylene concentration (IEC) and starch pattern indices (lower starch content), positively with higher chlorophyll content as indicated by the index of absorbance difference and with all minerals except N, as well as mineral ratios. In conditioned fruit, bitter pit incidence was correlated negatively with IEC, Ca, and positively with firmness, and all mineral ratios. Soft scald incidence in fruit stored at 0.5 °C was positively correlated with IEC and firmness, and all fruit mineral ratios except N/Ca and P/Ca, and negatively with Ca and Mg. For conditioned and unconditioned fruit stored at 3 °C, harvest indices predicted 27-28 % and 21-26 % bitter pit, respectively, while minerals and mineral ratios predicted 22-55 % and 18-54 % bitter pit, respectively. Harvest indices predicted 29-57 % soft scald, while minerals and mineral ratios predicted 29-49 for % soft scald for fruit stored at 0.5 °C. Correlations of bitter pit against P, K, and Mg were higher, and Ca and all mineral ratios lower, in conditioned fruit stored at 3 °C as opposed to those stored unconditioned at 3 °C. Nonlinear iterative partial least square algorithms based on variable importance plots vs coefficients showed that the regression of determination was affected by postharvest treatment in relation to harvest indices, minerals and their ratios. A negative correlation of bitter pit incidence against soft scald incidence was found for a region with high bitter pit and soft scald development.

Several pests and diseases infest apple during production, potentially causing heavy losses. Numerous pesticides are used to control pests and diseases, sprays of which contaminate the environment and result in pesticide residues. Among Good Agricultural Practices (GAPs), particle film technology (PFT) is promising for organic fruit production. Now some kaolin-based PFs such as Surround WP®, EclipseT, Anti-stress-500®, Parasol® have been developed which are available worldwide for commercial use. In India, preliminary research work was conducted for observing the effect of one kaolin-based PF (Surround WP®) on ‘Delicious’ apple. Five sprays of Surround WP® (3%) were applied to 20-randomly selected ‘Delicious’ apple trees each year during 2015–16 and 2016–17. The sprays were applied, starting on June 15 every year at fortnightly intervals and 20 unsprayed trees served as controls. Surround WP® reduced the incidence of San Jose scale (by ~ 64%), apple scab (by ~ 87%) and powdery mildew (by ~78%) significantly but increased the incidence of woolly apple aphid (by ~ 23%) compared to the control. Surround WP®- treated apples developed a better red color (Hunter ‘a’ value = 53.42 ± 0.42), increased anthocyanin content and improved appearance score. Surround WP® - treated apples were 35.4% firmer and contained a 49.9% higher Ca content compared to untreated fruit. Surround WP® treatment also showed significant improvement in soluble solids (increased by 10.5%) and ascorbic acid content (increased by 10.8%) with significant reduction in storage disorders such as bitter pit (reduced by 90.8%), brown core (reduced by 73.3%) and water core (reduced by 88.4%). Based on this study, Surround WP® can be recommended for organic production of ‘Delicious’ apples in Himachal Pradesh, India.

A field experiment with 31 rootstocks representing a genetically diverse group of rootstocks featuring ‘Honeycrisp’ as the scion was planted in 2010 at Geneva, NY USA. Rootstocks included three from the Malling series (UK), nine from the Budagovsky series (Russia), 16 from the Cornell Geneva series (USA) and three from the Pillnitz series (Germany). Over the first 8 years (2010–2017) we measured final tree size (trunk cross-sectional area: TCA) and cumulative yield. In the last 4 years we measured fruit soluble solids, bitter pit incidence, biennial bearing, and leaf zonal chlorosis. Tree size varied dramatically with the largest trees on B.70-20-20 and smallest trees on B.71-7-22. Setting the most vigorous rootstock at 100% we categorized rootstocks into 5 size categories: sub-dwarfing class (10–25%), dwarfing class (25–35%), semi-dwarfing class (35–50%), semi-vigorous category (50–70%) and vigorous class (70–100%). Cumulative yield varied 8 fold between the highest yielding rootstock (CG.3001) and the lowest yielding rootstock (B.71-7-22). We calculated theoretical yield per ha by multiplying cumulative yield per tree by a theoretical optimal tree density (trees/ha) based on tree size (TCA). The dwarfing rootstocks G.814, G.41TC, G.11 and B.10 had the highest yields per hectare while the most vigorous rootstocks B.70.20.20 and B.71-7-22 were the least productive. Theoretical cumulative yields varied from a high of 400 t/ha to a low of 50 t/ha, an 8-fold difference. Rootstock also influenced the incidence of bitter pit with the lowest levels of bitter pit with the rootstocks B.10, CG.2034, B.71-7-22, G.41N, CG.4003, G.202N, G.214, and Supporter 3. Considering bitter pit, yield, and optimum tree density, the theoretical yield of bitter pit free fruit varied from a high of 340 t/ha to a low of 35 t/ha, almost a 10-fold difference. The dwarfing rootstocks B.10, G.11, G.41TC, G.214 and G.814 had the highest yields per hectare of bitter pit free fruit. Rootstocks B.9 and M.26 had significantly lower cumulative bitter pit free yield/ha. These data indicate that rootstock not only has a large influence on mature tree cumulative yield but also bitter pit incidence which combine to create a large economic impact of rootstock choice on the long-term economic result of an orchard. This leads to the need for “designer rootstocks” which combine the rootstock characteristics needed to maximize the economic potential of each scion cultivar. info:eu-repo/semantics/acceptedVersion

Fruit susceptibility to Ca 2+ deficiency disorders has been associated cellular localization of Ca 2+ and Ca 2+ interactions with other nutrients. This study aimed to better understand the mechanisms regulating bitter pit (BP) development by comparing nutrient content and cell wall Ca 2+ binding capacity in ‘Fuji’ and ‘Granny Smith’ (GS) apples. After two months of storage at 0 °C, ‘Fuji’ apples had no BP, while GS apples had 52.5% BP incidence. Non-pitted GS fruit had higher flesh and skin Ca 2+ concentrations than pitted GS fruit, the latter having similar flesh and skin Ca 2+ concentrations to ‘Fuji’ fruit. Although ‘Fuji’ apples had the highest cell wall Ca 2+ concentration, most of the Ca 2+ shifted from the water-insoluble pectin into the water-soluble pectin fraction during storage. In GS, there was a large increase in the Ca 2+ concentration in water-insoluble pectin during storage and a small increase in Ca 2+ content in the water-soluble pectin. Pitted GS fruit had higher malic acid content, as well as higher [(K + + Mg 2+ )]/Ca 2+ and N/Ca 2+ ratios in flesh and skin tissues than non-pitted GS and ‘Fuji’ fruit. The results indicate that apple susceptibility to BP can be enhanced by increasing water-insoluble pectin Ca 2+ , as well as [(K + + Mg 2+ )]/Ca 2+ and N/Ca 2+ ratios in the fruit.

An effective method for predicting bitter pit incidence implemented before harvest could be a useful instrument for both the fruit industry and growers. Between 2009 and 2011, various methods for the prediction of bitter pit were evaluated at 60, 40, and 20 days before harvest (dbh) and at a commercial harvest in ‘Golden Smoothee’ apples. Four methodologies, two new ones (the development of natural bitter pit before harvest through the ‘passive method’ and bagging detached fruit before commercial ripening), and two of known efficacy under other conditions (infiltration with magnesium salts and maturity enhancement with ethephon dips) were assessed. To estimate the predictive accuracy of each method, bitter pit-like symptoms were related to the postharvest presence of bitter pit. The ‘passive method’ assesses bitter pit-like symptoms that appear naturally in fruit once they are picked from the tree, and left at room temperature during its evaluation. The ‘passive method’, as well as the infiltration with magnesium salts and ethephon dips, recognized bitter pit-like symptoms approximately 5–7 days after sampling (at 40 dbh) and showed significant correlation with the incidence of bitter pit after three months of cold storage. The ‘passive’ and ‘ethephon’ methods were also validated over two additional seasons in 30 and 16 different orchards, respectively. The results of these validations supported the efficacy of using the ‘passive method’ as the main method for predicting bitter pit, without having to use either reactive products or specialized equipment. This work was partially supported by the AECID Project A/021228/08 and by INIA Project RTA2009-00095. The authors are grateful to NUFRI and ACTEL, especially to Mr. JA Teixidor and Mr. Carlos Faro, and to their growers for providing the orchards.

The objective of this study was to evaluate the relationship between xylem functionality, calcium (Ca) deficiency and the incidence of bitter pit (BP) in ‘Fuji’ and ‘Catarina’ apples (low and high susceptibility to BP, respectively). Fruits were assessed for fresh weight, xylem functionality (of primary and secondary cortical vascular bundles) and mineral content (Ca, Mg, K, and N) during development (40–188 days after full bloom DAFB), as well as for the incidence (%) and severity of BP at commercial harvest (188 DAFB). During fruit development, ‘Catarina’ apples demonstrated an earlier loss of xylem functionality, lower Ca content, higher K content, and higher K/Ca, (K + Mg)/Ca and (K + Mg + N)/Ca ratios compared to ‘Fuji’ apples. The large loss in xylem functionality in ‘Catarina’ apples which led to a higher (K + Mg + N)/Ca ratio in the fruit seems to explain the higher susceptibility to BP as compared to ‘Fuji’. Showing with this, the xylem functionality may be a key physiological to infer about this disorder.

Calcium (Ca) deficiency in apples results in unwanted physical disorders in mature fruit that reduce fruit value. Ca deficiency associated with bitter pit is already prevalent early in the season, as it is initiated a few weeks after full bloom. Information regarding Ca concentration in reproductive buds or bud tissues is lacking, thus we investigated the Ca concentration in reproductive buds of the bitter pit susceptible ‘Braeburn’ and non-susceptible ‘Cripps Pink’ apple cultivars during the dormant season. Wavelength-dispersive x-ray spectroscopy (WD SEM) was used to quantify total Ca concentration of parenchyma and vascular tissues, from June to September, for two seasons (2012 and 2014). Results showed a changing trend in Ca concentration from June to September for total Ca concentration and between cultivars. Total Ca concentration was the highest in ‘Cripps Pink’ during the whole period and related to the non-susceptibly to Ca related disorders. Ca concentration in ‘Cripps Pink’ declined towards September in contrast with the increasing trend of ‘Braeburn’. This may indicate that the total Ca concentration of the buds, and not the change of Ca concentration in buds during winter, is associated with a higher Ca status of fruit on non-susceptible cultivars. The actual Ca concentration of ‘Cripps Pink’ at the end of August was still higher than that of ‘Braeburn’. Results may be explained partly by the time of primary xylem formation in the bud, which happens earlier in ‘Cripps Pink’, as well as the associated increase in Ca translocation, indicating the role of generic differences between cultivars, contributing towards final changes in the inherent Ca concentration at the beginning of the dormant season.

a b s t r a c t Bitter pit (BP) is a physiological disorder in apple (Malus × domestica Borkh) believed to be triggered by low Ca 2+ concentrations in the fruit, and which may be influenced by environmental conditions. The objectives of this study were to explore the effects of tree shading on total and cell wall bound fruit Ca2+ content and fruit susceptibility to BP. 'Greensleeves' (GS) apple trees were cultivated under shaded and non-shaded conditions. The shading condition was applied 70 days after full bloom by reducing about 50% of the sunlight reaching the tree canopies. Shading increased stem water potential and leaf stomatal conductance. Bitter pit was observed only in shaded fruit. Cortical Ca2+ was most abundant in shaded fruit without BP symptoms, intermediary in shaded fruit with BP, and lowest in non-shaded fruit. The cell wall Ca 2+ concentration was higher in shaded than non-shaded fruit, but shaded fruit with and without BP had similar cell wall Ca 2+

Bitter pit (BP) is a physiological disorder in apple commonly associated with high Mg/Ca ratio in fruit tissue. This work was carried out to identify the best fruit tissue sampling method for Ca and Mg assessment to discriminate ‘Fuji’ apples regarding the occurrence of BP. After six months under controlled atmosphere storage (2.0 kPa O2 + 0.5 kPa CO2, at 0.5 °C/90–95% RH), fruit without or with BP were submitted to Ca and Mg analysis (mg kg−1 of fresh weight) in the total fraction (TF) of peel + flesh, and in the TF and soluble fraction (SF) of flesh or peel tissues. For the peel + flesh, a wedge-shaped segment was cut longitudinally from the fruit (with 1 cm wide at the equatorial region), discarding the core tissue. For individual sampling of the peel (thickness of 0–2 mm) or flesh (thickness of 2–8 mm), the fruit were cut along the equatorial region, so that only the distal end was used. In this portion of the fruit, Ca and Mg contents were higher in the peel than in the flesh in the TF, and lower in the peel than in the flesh in the SF, while the Mg/Ca ratios in TF and SF fractions were higher in the flesh than in the peel, regardless the occurrence of BP. Calcium and Mg contents in the SF relative to the TF were very low in both peel and flesh tissues. Calcium in the SF represented 0.36% and 2.79% of its content in the TF for peel and flesh, respectively. Magnesium content in the SF represented 0.70% and 3.74% of that in the TF for peel and flesh, respectively. Fruit without BP showed higher Ca content and lower Mg/Ca ratio in the TF of peel + flesh, peel or flesh, and in the SF of peel or flesh, compared to fruit with BP. Fruit without BP also showed a higher percentage of Ca in the SF in relation to TF in the peel (0.42%) compared to fruit with BP (0.31%). Fruit without BP also showed lower Mg content in TF of peel + flesh and peel, and in the SF of the flesh. There was no difference between fruit with and without BP only for Mg contents in TF of the flesh and SF of the peel. The canonical discriminant analysis showed that the Mg/Ca ratio in the SF of the peel tissue at the distal end of the fruit provides the best method to discriminate fruit without and with BP, which can be potentially used as a tool to predict BP development in ‘Fuji’ apples.

‘Reinette du Canada’ (RC) and ‘Reinette Grise du Canada’ (RG) apple (Malus × domestica Borkh) cultivars declared throughout the Community as Protected Designation of Origin ‘Manzana Reineta del Bierzo’ are severely affected by bitter-pit during storage. Pre-harvest treatments with calcium carbonate, authorized in organic production, and bio-activator Harpin protein were used to assess the effect on quality at harvest and during cold storage in both apple cultivars during 2007 and 2008. Bitter-pit at the end of storage was higher in ‘RC’ than in ‘RG’, due to the fact that K/Ca ratio in fruit was higher in ‘RC’. Harpin protein did not improve the quality of ‘Reinette’ apple cultivars. Calcium carbonate pre-harvest treatments were useful to decrease external and internal bitter-pit incidence of ‘Reinette’ apple cultivars after 90 days of storage, but differences at the end of storage were not significant. Therefore, calcium carbonate would be a useful product in organic production in order to decrease bitter-pit incidence in ‘Reinette’ apple cultivars during medium term storage.

Covering apple orchards with nets protects them from hailstorms but this changes the amount and quality of the light supplied to the trees. This study was carried out to assess the effects of shade provided by white protection net on yield and fruit quality of apple orchards in Southern Brazil, along three growing seasons (2002/2003, 2003/2004, and 2004/2005). ‘Gala’ and ‘Fuji’ apple trees (on MM111 rootstock, raised as slender spindles, with a spacing of 5.5 m × 3 m) were left uncovered (control trees) or covered with white net. The white net reduced the photosynthetically active radiation ( λ = 400–700 nm) accumulated over the trees’ canopy along a day by 18.4%, leading to a higher leaf chlorophyll content in both cultivars, and a higher specific leaf area in ‘Gala’. The shade provided by the net did not affect yield and increased fruit average weight in both cultivars. At harvest, the number of seeds per fruit and severity of russet were not affected by netting in both cultivars, as well as the incidence of watercore in ‘Fuji’. The main beneficial effects of the white net were the reduced incidence of sunburn on ‘Gala’, reduced incidence of bitter pit during cold storage in both cultivars, and reduced incidence of apple scab at harvest and of decay after cold storage in ‘Fuji’. Fruit fly damage in ‘Gala’ (assessed in one season) was reduced by netting. However, netting affected negatively some fruit quality attributes. ‘Gala’ and ‘Fuji’ apples from trees protected by the net had a poor skin color (pale blush and a more intense green background color) at harvest. The net reduced flesh firmness and SSC, and increased the starch index of ‘Gala’ apples at harvest, and reduced flesh firmness and SSC, assessed after cold storage and shelf life, in fruits of both cultivars.

Calcium treatment of apple ( Malus × domestica Borkh.) fruit is a widely used practice aimed mainly at avoiding the development of bitter pit. However, very few studies have reported the effects of such treatments on the production of flavour-related volatile compounds, despite the relevance of aroma and taste for overall quality. In this study, commercially mature ‘Golden Reinders’ apples were dipped in 2% (w/v) calcium chloride prior to storage at 1 °C and 92% RH under either air, standard controlled atmosphere (SCA; 3 kPa O 2 :2 kPa CO 2 ) or ultra-low oxygen atmosphere (ULO; 1 kPa O 2 :2 kPa CO 2 ) for 19 or 31 weeks, and subsequent removal to 20 °C for 7 d, after which the emission of aroma-related volatile compounds and a number of maturity and standard quality parameters were assessed. Calcium treatment notably enhanced the production of aroma volatile compounds after mid-term storage under air and, to a lesser extent, under SCA. Retention of titratable acidity (TA) was also improved in air-stored fruit in response to calcium treatment, while no effects on firmness were observed. Although ULO-stored samples showed the highest firmness and TA values under storage, aroma volatile production was severely depleted, and calcium treatment could not overcome this inhibition. It is therefore suggested that calcium applications allow improving aroma quality while preserving adequate levels of key standard quality parameters after mid-term storage of ‘Golden Reinders’ fruit, and are thus a simple and economical alternative to CA storage of this apple cultivar.

Bitter pit (BP), a Ca2+ deficiency disorder of apple fruit (Malus domestica), is a complex process that involves not only the total input of Ca2+ into the fruit, but also a proper Ca2+ homeostasis at the cellular level. The objective of this study was to test the hypothesis that Ca2+ accumulation into storage organelles and binding to the cell wall is associated with BP development in apple fruit. The experiment was carried out on ‘Granny Smith’ apples stored at 0 °C for 60 d. After storage, fruit were segregated into two lots for analysis, apples with the water-soaked initial visual symptoms of BP and those not showing this symptom. Cytochemical and ultrastructural observations showed an accumulation of Ca2+ in the vacuole of individual outer cortical cells of pitted fruit. We also observed an increase in the expression of genes encoding four pectin methylesterases, a greater degree of pectin deesterification and therefore more Ca2+ binding sites in the cell wall, and a higher fraction of the total cortical tissue Ca2+ content that was bound to the cell wall in pitted fruit compared with non-pitted fruit. Cells of the outer cortical tissue of pitted fruit consistently had higher membrane permeability than outer cortical cells of non-pitted fruit. The results provide evidence that Ca2+ accumulation into storage organelles and Ca2+ binding to the cell wall represent important contributors to BP development in apple fruit.

In all major apple producing countries, applications of foliar calcium (Ca) products to increase fruit Ca content and reduce the incidence of bitter pit in apples are used. Calcium nitrate (Ca(NO3)2), Calcimax and Ca acetate were applied, commencing at three different developmental stages (early, mid and late) of fruit growth. Late Ca(NO3)2 (80 days after full bloom (dafb)) applications increased the Ca content of fruit at harvest more than early (six dafb) and mid (40 dafb) applications. There was a trend towards an increase in bitter pit from early to late applications of Ca(NO3)2 and Calcimax, confirming previous results obtained when applying only Ca(NO3)2. In spite of the very low incidences of bitter pit during these seasons (less than 7%), significant differences between treatments were found between Ca(NO3)2 Mid and other treatments in 2004/2005, as well as Ca(NO3)2 and Calcimax Early and other treatments in 2005/2006. Ca acetate applications did not show any trends in fruit Ca content or bitter pit incidence when applied during the three stages. Thus, products may differ in efficiency of Ca absorption and effectiveness in decreasing bitter pit in fruit when applied during different developmental stages. © 2008 Elsevier B.V. All rights reserved.

Bitter pit in apples still causes significant losses, especially in the export markets of ‘Golden Delicious’ apples from South Africa. Orchard practices to reduce the possibility of bitter pit are followed, as well as destructive methods to predict the probability thereof, but the occurrence of bitter pit is still unacceptably high. Fluorescence imaging is a fast, non-destructive technique, able to evaluate numerous fruit within a short time span. By applying fluorescence imaging on individual fruit before any symptoms of bitter pit were apparent, lower fluorescence was shown to be associated with bitter pit development in apples in selective cases. Our results showed that, using averaged cumulative distribution functions (CDFs) of pitted and non-pitted fruit classes, it was possible to show a difference between these classes with fluorescence imaging. However, the individual distinction between all pitted and non-pitted fruit of our total sample, could not been defined as clearly. In the majority of cases, on a single fruit basis, separation in groups was not satisfactory (less than 100% accurate) based on industry requirements for a prediction technique. Results of pre-harvest imaging on apples to identify fruit with bitter pit potential at harvest showed that pitted fruit were correctly classified (75–100%). However, misclassification of non-pitted fruit (50% and less) with fluorescence imaging is still too high to be of any commercial use.

A hyperspectral NIR imaging system was developed to identify bitter pit lesions on apples. A discriminant PLS calibration model was constructed to discriminate between pixels of unaffected apple skin and bitter pit lesions. The calibration model was successfully validated on a different apple. The system was able to identify bitter pit lesions, even when not visible to the naked eye such as just after harvest, but could not discriminate between bitter pit lesions and corky tissue. The reduced luminosity at the boundary of the image caused in one image some misclassification errors.

The influence of a pre-storage, 7-day, 20 °C warming period on post-harvest apple ( Malus xdomestica Borkh.) fruit quality and disorder expression—soft scald and low temperature breakdown in particular, were investigated in ‘Honeycrisp’ fruit grown in the Annapolis Valley of Nova Scotia. The apples from 7-year old trees were harvested from three commercial sites on Sept 30, 2002 (early) and Oct 10, 2002 (late), after which, half of the fruit was immediately cooled to 5 °C (control), while the other half was held for 7 days at 20 °C (delayed cooling treatment). Both the control and delay cooled apples were then stored at either 3 or 5 °C in controlled atmosphere (CA) (2.5 kPa O 2 ; 1–1.5 kPa CO 2 ) or refrigerated air (RA) storage for 4 and 6 months. Fruit quality measurements and disorder incidence were recorded following storage removal and a 7-day shelf-life at 20 °C. Delayed cooling had no effect on fruit firmness, soluble solids (%), titratable acidity, epidermal greasiness, senescent breakdown, and bitter pit (the incidence of these latter disorders was low), while moisture loss from the delay cooled fruit ranged from 1.2 to 1.3% following the 7-day treatment. Delayed cooling strongly suppressed the development of the storage disorders soft scald and low temperature breakdown, which in the control fruit reached upwards to 30% of the sample. No CA- or RA-related differences in these disorders were observed in the fruit receiving the pre-storage delayed cooling treatment. Storage rot was not influenced by delayed cooling and was present in upwards to 32% of the fruit from the late-harvested apples after 6 months of storage. In regions where soft scald and low temperature breakdown are serious postharvest problems, it appears that a delayed cooling period prior to storage will help minimize economic loss.

Empire and Golden Delicious apples were classified based on their surface quality conditions using backpropagation neural networks (BPNN) and statistical classifiers such as decision tree (DT), K nearest neighbour (K-NN) and Bayesian with textural features (and histogram features only with the BPNN classifier) extracted using all the pixels in an entire apple image. Two classification applications were performed: two subsets that included a defective (or stem/calyx) apple group and a good apple group; and five subsets that included all the defective (leaf roller, bruise and puncture on Empire, and bruise bitter pit and russet on Golden Delicious) and good apple groups (good tissue and stem/calyx views). With two subsets, classification accuracy using textural features ranged between 72·2 and 100% for Empire apples while it ranged between 76·5 and 100% for Golden Delicious apples. Results obtained using histogram features were significantly lower than the other classification applications. With five subsets, slightly lower recognition accuracies were obtained; the BPNN using textural features performed 93·8% success rate in recognising Empire apples. However, for Golden Delicious apples, all the classifiers produced similar accuracy rates ranging between 85·9 and 89·7%. Results obtained from the BPNN using histogram features were significantly lower than the classification applications using textural features.

‘Honeycrisp’ apple [( Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.] fruit are susceptible to the storage disorders soggy breakdown, soft scald, and bitter pit. The effects of low and high temperature storage regimes (0 or 0.5 °C and 2.2, 2.8 or 3 °C, respectively), diphenylamine (DPA) treatment, and delays at 10 or 20 °C before storage, were investigated. Soggy breakdown and soft scald incidence is highest at the lowest temperatures of 0 or 0.5 °C and reduced or eliminated by storage at the higher temperatures. DPA sometimes reduced, but did not eliminate, soft scald. Both soggy breakdown and soft scald were markedly reduced or eliminated however, by keeping fruit at 10 or 20 °C before storage regardless of storage temperature. Bitter pit incidence was sometimes increased by delay treatments and storage at higher temperatures. Little effect of any treatment on firmness, soluble solids content, internal ethylene concentration (IEC), background color and titratable acidity was detected.

This paper shows how the information enclosed in a colour image of a bi-colour apple can be used to segment defects. A method to segment pixels, based on a Bayesian classification process, is proposed. The colour frequency distributions of the healthy tissue and of the defects were used to estimate the probability distribution of each class. The results showed that most defects, namely bitter pit, fungi attack, scar tissue, frost damages, bruises, insect attack and scab, are segmented. However, russet was sometimes confused with the transition area between ground and blush colour.

Induction of bitter pit-like symptoms (Mg2+ induced pits [MgIP]) on Northern Spy apples (Malus domestica borkh.) by infiltrating Mg2+ salt solutions into the fruits was positively correlated with bitter pit that developed naturally during storage. Fruits at harvest were infiltrated with 0.1 M MgCl2 in 0.3 M sorbitol with 0.1% Tween 20 and placed at 20°C for 10 days (d) after which the number of MgIP was determined on individual fruits. A parallel sample of fruits from each orchard was stored at 5°C in air (both years) and at 3°C in air or controlled atmosphere (CA) storage in the second year. MgIP was positively correlated with bitter pit development in storage for fruits harvested 20 d and 10 d before and at optimal maturity for long-term storage. The endogenous (native) fruit Ca2+ concentration was inversely related to the number of pits induced by Mg2+ and to bitter pit development following storage.

Granny Smith apples grown in Western Australia are highly susceptible to the physiological disorders bitter pit and superficial scald, after short periods of storage. Granny Smith apples were held in sealed polyethylene bags with and without an ethylene absorbent Purafil (potassium permanganate on aluminium oxide). In two seasons the ethylene levels were markedly reduced with the use of potassium permanganate while the severity of bitter pit and superficial scald were also reduced. These effects of ethylene removal may be due to the delaying of fruit senescence.

Golden Delicious apples ( Malus domestica Borkh) were vacuum-infiltrated with Mg +2 and Ca +2 alone or in combination at concentrations ranging from 0.01 to 3.36 M as the chloride salt with 0.4 M sorbitol. Fruit infiltrated with Mg +2 alone and stored 2 weeks at 20°C developed bitter pit-like symptoms that were positively correlated with Mg ++ concentration infiltrated. Infiltration with Ca +2 induced no bitter pit-like symptoms. Bitter pit symptoms induced by Mg +2 were decreased, or did not develop when Ca +2 was included in the infiltration medium at concentrations of 0.01, 0.02 and 0.04 M , respectively. The native (endogenous) Ca +2 concentration (ppm dwt) of individual fruits was inversely related to the number of lesions induced by Mg +2 infiltration.

A field study was conducted to induce bitter pit in cultivar ‘Sundale Spur Golden Delicious’ (Malus domestica Borkh.) apple. Fruiting spurs were sprayed with 1% (w/v) CaCl2 and 1% (w/v) MgCl2 every 10 days, beginning 5 days after full bloom, and/or shaded with brown paper bags. The effect of MgCl2 spray and bag + MgCl2 treatments on the fruiting spurs was increased bitter pit incidence, decreased fruit calcium, increased fruit magnesium and potassium, and decreased number of fruit per spur. Bagging the fruit resulted in a 4-fold increase in bitter pit incidence, and a significant reduction in fruit calcium content and fruit weight over the control. In contrast, CaCl2 spray slightly reduced bitter pit, increased fruit calcium, reduced fruit magnesium and increased the number of fruit per spur. The incidence of bitter pit ranged from 8% (CaCl2 spray alone) to 88% (bag + MgCl2). Overall, the combinations of bagging and cation sprays induced a wide range of bitter pit incidence in apple fruit which can be reliably used for future study of the disorder.

Transport of 45 Ca 2+ across enzymically isolated cuticles from apple fruit ( Malus domestica Borkh. cultivar ‘Granny Smith’) was followed in an apparatus where the cuticle was clamped between two solutions, and the appearance of 45 Ca 2+ recorded in the sampling solution. 45 Ca 2+ transport from the outer to the inner surface of the cuticle could be increased by some surfactants when they were exposed to the inner, non-waxy surface. Addition of Armoblen T25 and Tween 20 increased the transport rate, Agral LN had little effect and Armoblen NPX inhibited transport. When the surfactants were applied to the outer surface there was little effect, except with Armoblen NPX where transport declined. As the cuticles did not contain any cracks or functional lenticels these results suggest that the surfactants increased Ca 2+ transport by altering the permeability of the cuticle as a result of having direct access to the cutin and polysaccharide matrix.

The relationship between pyruvate kinase (pyruvate-ATP phosphotransferase, EC 2.7.1.40) activity, fruit cation concentration (Ca2+, Mg2+ and K+) and bitter pit in apple cultivar ‘Smoothie Golden Delicious’ fruit (Malus domestica Borkh.) was investigated. Fruit was sprayed with 1% (w/v) CaCl2, 1% (w/v) MgCl2 or a combination of both chemicals every 10 days, beginning 5 days after full bloom, in a factorial experiment designed to induce a range of post-storage bitter pit symptoms. Pyruvate kinase activity during the early stages of fruit growth was higher in fruit from treatments which developed 100% bitter pit after storage than in fruit from treatments that developed only 3% bitter pit. Fruit with a higher bitter pit incidence had a lower Ca2+:Mg2++K+ ratio than fruit with a low level of the disorder. There was a positive correlation between pyruvate kinase activity during the early stages of fruit development and bitter pit incidence after storage. Correlation coefficients (r) were highest in June (r=0.96), declined steadily until harvest (r=0.67) and were lowest after storage (r=0.12). Preliminary data indicate that an assay for pyruvate kinase may be valuable for early prediction of post-harvest bitter pit development and cation ratio.

Three different water status conditions (full watered, mild deficit and high deficit) were applied to cultivar ‘Granny Smith’ apple trees growing in pots during two periods of 4 weeks (last phase of fruit growth by cell division and middle phase of fruit growth by cell enlargement). In the first period, water deficit strongly reduced shoot, leaf and fruit growth, increased the calcium content in leaves and reduced the appearance of bitter pit in fruits. When applied in the second period, water deficit reduced leaf weight and fruit growth, increased the calcium content in leaves and reduced the appearance of bitter pit in fruits. Leaf sap osmolarity was lowered by the water deficit condition. These results are discussed with regard to patterns of diurnal water status in the differently watered trees.

Phorone and 20 other compounds related synthetically or structurally were evaluated for their effect on the development of core flush, superficial scald and bitter pit in apples during storage. Phorone gave a marked reduction in disorders in all studies. 5-methylhept-4-one was the only other compound that consistently reduced disorder levels but it was less effective that phorone.

In a pot experiment with apple trees, cultivar ‘Cox's Orange’, Ca was omitted in the nutrient solution for periods of different length. Trees lacking Ca in the latest 2 3 of the growth period contained 42 mg kg−1 Ca in the fruits, which is 21% below control. In the bulked sample, average size of fruits was not considerably affected, but the distribution of small and large fruits changed toward more smaller fruits. Concommitantly, bitter pit was reduced compared to the control. Sufficient K supply (1.20–1.70% K in leaf dry matter) given to trees receiving high Ca supply depressed Ca concentration in the fruits to 41 mg kg−1, which is 23% below control. Average fruit size was not significantly changed, but the distribution was towards larger fruits. Under these circumstances bitter pit was increased. Ca deficiency, caused either by omission of Ca or competition between K and Ca, increased fruit rot, russeting and cracks on the fruits. Short term variations in Ca levels were not seen to produce any measurable response.

The concentrations of the mineral elements K, Ca, Mg, P, S and Cl were compared in pitted and sound tissues of mature fruits of the apple cultivars ‘Akane’, ‘Reine des Reinettes’ and ‘Idared’ using an electron microprobe. Mg, Ca and to a lesser extent S were always present in higher concentrations in pitted areas than in non-pitted ones, in the ratio of 3.0 to 14.4 for Mg and 3.1 to 7.9 for Ca. The K concentration in pitted tissues was variable showing no significant difference in ‘Akane’, and an increase or decrease in ‘Reine des Reinettes’ and ‘Idared’, respectively. P and Cl concentrations were also variable. Serious perturbations were found in the ionic content of the pitted tissues affecting several elements implicated in essential physiological processes.

‘Maygold’ apples were dipped in CaCl 2 or GA 3 as post-harvest treatments. Bitter pit was reduced by CaCl 2 and GA 3 . Pitted fruits always had low Ca 2+ levels. The cellular fractionation of the flesh tissue of untreated apples showed a negative correlation between soluble Ca 2+ , acid labile Ca 2+ and bitter pit. An increase of Ca 2+ in these fractions by means of CaCl 2 treatments did not prevent the disorder. GA 3 , at the more effective concentration for protecting fruits, increased the soluble Ca 2+ of pitted flesh tissue. The possibility that the disorder is linked to an alteration of the Ca 2+ transport mechanism at cell level is suggested as a plausible explanation.

Incidence of the physiological disorder bitter pit was reduced by storage of cultivar ‘Cox's Orange Pippin’ apples at 1°C in 25-μm thickness polyethylene bags (polybags) in which there were a number of 1-mm microperforations. Concentrations of CO 2 increased and O 2 decreased as the number of microperforations per bag was reduced. These changes were associated with reduced levels of bitter pit. It is suggested that 50–70 microperforations per polybag, of sufficient size to fit inside an 18.5-kg carton, could be used commercially to reduce bitter pit and maintain quality of fruit stored for 6 weeks at 1°C, and then kept at ambient temperatures within the polybags for an additional 7 days. The effectiveness of microperforated polybags and vacuum infiltration with CaCl 2 in reducing bitter pit was compared over 3 seasons. The results were variable, with polybags being more effective than vacuum treatment in 2 of the 3 seasons, and vacuum treatment better than polybags in 1 season. Neither method reduced bitter pit to commercially acceptable levels when the non-treated fruit had levels of bitter pit exceeding 20–30%. When apples were placed in microperforated polybags after vacuum infiltration, up to 20% developed a brown-heart-like disorder.

Calcium (Ca), magnesium (Mg) and potassium (K) concentrations and distribution have been measured in apple fruit treated with Ca sprays during the growing season, and in stored fruit after post-harvest vacuum-infiltration of Ca or Mg, for bitter pit control. The highest concentrations of each cation occurred in the skin and core, the lowest in the outer cortex. Ca sprays increased Ca levels in each tissue segment; K levels were lower in Ca-sprayed fruit, but effects on Mg were variable. Concentrations of all 3 cations in the outer cortex increased during storage. Vacuum-infiltration of Ca substantially increased Ca levels in the outer 12 mm of cortical flesh after 2 weeks in storage, but did not affect Mg or K concentrations. Vacuum-infiltration of Mg resulted in an increase in Mg concentration in the outermost segment of flesh, but had little effect on levels elsewhere in the tissue, or on the concentrations of other ions. Ca added to fruit, either by spray or vacuum-infiltration, could easily leak from tissue in experiments with tissue disks. This leakage reduced tissue Ca concentrations to a level common to all treatments, indicating that Ca externally applied was probably located in the free space, and not involved with maintaining cell structure and function.

‘Cox's Orange’ fruits were treated on the tree at weekly intervals with high concentrations of either Ca or Mg solutions. The concentration of these elements in the treated fruits was considerably increased. Ca treatment completely prevented the development of bitter pit, reduced respiration and solute leakage, and increased fruit firmness and titratable acidity. The effect of Mg on the investigated fruit characteristics was different in the two years under consideration, which possibly can be explained by the highly different Ca Mg ratios obtained in the two years.

The role of Ca and Mg in the enzymatic browning of ‘Golden Delicious’ apples was explored. Enzymatic browning due to polyphenol oxidase (PPO) was stimulated with the addition of 0.8–10 mM MgCl2 to the reaction mixture, whereas 0.8–10 mM CaCl2 had little effect or decreased the rate of enzymatic browning. Within a week after vacuum infiltration with MgCl2, treated fruits exhibited browning symptoms that were similar to bitter pit. Six months after vacuum infiltration, when analyzed for enzyme activity, MgCl2-treated fruits exhibited higher rates of PPO activity, whereas CaCl2-treated fruits had lower activity than the MgCl2-treated fruits and the controls. A hypothesis is advanced that the initial visible symptoms of bitter pit, i.e. the localized browning, is caused by PPO, its activity being stimulated by the localized Mg/Ca imbalance present in the tissue. The results indicate that Ca is predominant in the prevention of this disorder, whereas a deficiency of Ca is involved in its induction.

Controlled and modified atmospheres reduced bitter pit in New Zealand ‘Cox's Orange Pippin’ apples stored for 5 weeks at 2°C. Fruit from orchards that had received calcium sprays during the season were stored in an integral container maintained with a gas atmosphere of 3% CO2 plus 3% O2, and had less than 6% bitter pit. In comparison, air-stored fruit from the same orchards had up to 26% bitter pit. Polyethylene bags containing different numbers of 9-mm holes were tested for their effectiveness in influencing bitter pit development. The incidence of bitter pit that developed during storage was progressively reduced from 50% to less than 5% as the number of holes per bag decreased. Fruit in polybags had less weight loss, higher firmness and improved quality compared with air-stored fruit. Practical problems relating to commercial use of polybags for bitter pit control are discussed.

This study involved storing samples of ‘Cox's Orange Pippin’ from the 1974 and 1975 crops from each of 2 rootstock trials. After 12 weeks cool storage, the samples were examined for bitter pit and internal breakdown. In the high-pit year 1974, ‘Cox's Orange’ on ‘M.16’ and ‘MM.115’ had significantly more pit and breakdown than when grown on ‘MM.106’, ‘MM.112’ and ‘MM.114’, with fruit from ‘MM.104’ in between the 2 groups. However, in the low-pit year 1975 there were no differences. In the second trial in 1974, ‘Cox's Orange’ on ‘M.16’ had significantly more pit and breakdown than when on ‘Northern Spy’, ‘MM.109’ and ‘M.7’. In the following year there were no differences in the incidence of pit, but fruit from ‘M.7’ and ‘M.2’ had more breakdown than from other rootstocks in this trial.