Apple Fruit Quality Research Articles

Salicylic acid treatment inhibits ethylene synthesis and starch-sugar conversion to maintain apple fruit quality during shelf life

Starch and sugars are widely acknowledged as taste determinants, energy substances, and signal molecules in fruits. Salicylic acid (SA) regulates many physiological and biochemical processes during fruit ripening. In this work, we investigated the effects of SA treatment on physiological parameters and SA synthesis, ethylene production, and starch-sugar metabolism of apples during shelf life. Results showed that SA maintained fruit firmness, reduced weight loss, and inhibited starch to sugar conversion during shelf life. The endogenous SA level was increased in SA-treated fruits, mediated by MdPAL, MdICS2, and MdNPR1, thus decreasing MdACS1 and MdACO1 expressions and inhibiting ethylene biosynthesis. Furthermore, the expression of starch and sugar-related genes, MdAMY, MdBam5, MdBam8, MdSPS, MdSUSY, MdNINV, and MdAINV, were inhibited by SA treatment during shelf life. It was inferred that exogenous SA could inhibit ethylene synthesis and starch-sugar conversion, maintain the quality, and prolong the shelf life of apples

Dependence of apple productivity and fruit quality on the method of drip irrigation terms appointment

Dependence of apple productivity and fruit quality on the method of drip irrigation terms appointment

Salicylic acid and nutrient sprays to improve apple fruit quality

Maturity at harvest is one of the most important properties that determine the final quality of the apple fruit. Appearance, texture, flavour and nutritional value are qualities that consumers evaluate empirically to decide whether to eat the fruit again. Within agricultural practices in and out of the orchard, the relationship between plant nutrition and fruit quality is important, and proper nutrient balance is essential to maintain fruit quality. This research work was carried out on ‘Golden Delicious’ and ‘Red Chief’ apple trees. A 56 factorial arrangement was used, with 5 concentrations and 6 factors, 25 treatments in a Taguchi L25 structure. Improvements were found in parameters for fruit finish and fruit quality. The factors with the greatest positive effect on quality in order of importance were Salicylic Acid (SA) 1.0 mM, Potassium (K) 58.90 mM, Molybdenum (Mo) 0.516 mM, Calcium (Ca) 70.00 mM and Cobalt (Co) 8.248 mM and in order of importance the following variables: TSS/acidity ratio, total soluble solids TSS, antioxidant capacity (AC), total phenols (TF), and titratable acidity (TA) in ‘Golden Delicious’ apple. Considering ‘Red Chief’, the factors Ca 70.00 mM, K 58.79 mM and SA 1.0 mM, with the variables; TA, TSS/acidity ratio, TF, TSS and AC that finally lead to an optimal development of finish and quality in the apple fruit.

A genome-wide association study provides insights into fatty acid synthesis and metabolism in Malus fruits.

As a precursor of aromatic compounds, fatty acids play important roles in apple fruit quality; however, the genetic and molecular basis underlying fatty acid synthesis and metabolism is largely unknown. In this study, we conducted a genome-wide association study (GWAS) of seven fatty acids using genomic data of 149 Malus accessions and identified 232 significant signals (-log10P>5) associated with 99 genes from GWAS of four fatty acids across 2 years. Among these, a significant GWAS signal associated with linoleic acid was identified in the transcriptional regulator SUPERMAN-like (SUP) MD13G1209600 at chromosome 13 of M. × domestica. Transient overexpression of MdSUP increased the contents of linoleic and linolenic acids and of three aromatic components in the fruit. Our study provides genetic and molecular information for improving the flavor and nutritional value of apple.

Dynamic controlled atmosphere: Does the frequency of respiratory quotient determination during storage affect apple fruit metabolism and quality?

This study aimed to determine the effects of the frequency of respiratory quotient (RQ) determination during storage in a dynamic controlled atmosphere (DCA-RQ) on the anaerobic metabolism and quality of ‘Galaxy’ apples during two seasons. Another aim was to identify a relationship between the RQ determination frequency and the RQ level adopted in the metabolism and quality of apples after long-term storage. Fruit were harvested at the commercial harvest peak and stored for nine months under controlled atmosphere (CA) and DCA-RQ 1.3 and 1.5 conditions, with four frequencies of RQ determination: once a week, twice a week, daily, and without RQ determination. Storage under DCA-RQ and the RQ determination frequency affected fruit metabolism and quality. Daily RQ determination induced ethylene production under DCA-RQ 1.5 due to frequent low oxygen stress. The daily RQ determination also induced higher anaerobic metabolism, flesh breakdown, and decay incidence, making a daily RQ determination in both RQ levels tested not recommended. Fruit quality was better maintained when the RQ determination frequency was once and twice a week for DCA-RQ 1.3 and twice a week for DCA-RQ 1.5, resulting in higher quantities of healthy fruit and higher flesh firmness maintenance without inducing excessive anaerobic metabolism compounds production. The RQ determination frequency has more influence on anaerobic metabolism induction than lowering the oxygen from 1.2 kPa (CA) to 0.15 kPa (DCA-RQ 1.5), which evidences that there are two main ways to manage anaerobic metabolism induction in ‘Galaxy’ apples: changing the RQ level adopted and changing the RQ determination frequency. Without the stress caused by RQ determination, storage under DCA-RQ conditions does not result in quality maintenance compared to fruit submitted to RQ determination.

Intra-canopy variability in apple fruit quality is great

Intra-canopy variability in apple fruit quality is great

Fruit quality of ‘Gala’ and ‘Fuji’ apples cultivated under different environmental conditions

This study evaluated the effect of growing site environmental conditions on apple fruit quality. Experimental orchards with ‘Gala’ and ‘Fuji’ apple strains were established in the subtropical humid climate in Southern Brazil, between 26° and 28°S, in the growing sites of São Joaquim, Caçador and Vacaria, located 1415, 960, and 971 m, respectively, above sea level. Fruit quality was assessed at harvest and after storage from the 5th through 8th year after planting. At each growing site, ‘Gala’ apples were harvested at one maturity stage and stored in a controlled atmosphere (CA). ‘Fuji’ apples were harvested at two maturity stages, with early harvested fruit stored in air and late harvested fruit stored in CA. For the São Joaquim site compared with those of Caçador and Vacaria, average temperature during the growing season was lower whereas the number of winter chilling hours and the number of days from bloom to harvest were higher. Fruit weight and red skin area were higher and russeting skin index lower in fruit from the coldest site (São Joaquim) for both cultivars. At harvest, flesh firmness and starch index of fruit from the coldest site were higher or the same as those of the warmest sites (Caçador and Vacaria), depending on cultivar and harvest date. The rate of flesh firmness loss during storage was greater in fruit from the coldest growing site for both cultivars and harvest maturities. Titratable acidity (TA) and soluble solids content (SSC) in fruit from the warmest site were higher or the same as the fruit from the coldest site, depending on when fruit analysis were performed. Although ‘Gala’ apples produced in all three growing sites were equally affected by external fungal decay, fruit from the warmest site had the highest incidence of Glomerella cingulata spot. ‘Fuji’ apples produced in the coldest site had the highest length/diameter ratio and watercore index at harvest and developed more CO2 injury and diffuse flesh browning. External fungal decay index for ‘Fuji’ was the same for the three growing sites for fruit harvested at early maturity, but the decay index was higher for fruit from the warmest site when harvested at an advanced maturity. The study shows the influence of environmental conditions on apple fruit growth and development and the need to adjust production and storage practices to achieve high fruit quality based on pre-harvest environment.

Pruning type and tree growth control methods influence apple yield and fruit quality

Pruning type and tree growth control methods influence apple yield and fruit quality

The biochemical and physiological basis for hard cider apple fruit quality

Societal Impact StatementFermented “hard” cider is currently experiencing a resurgence in popularity. While there is a long history of cultivating apple trees with fruit quality characteristics intended specifically for cider production, there is a dearth of cider‐specific apple production in many emerging cider producing regions, such as North America. To help bolster the emerging cider industry and identify topics that warrant further research, this review article describes the biochemistry and physiology of apple fruit quality from a cider producing perspective.SummaryThe United States and Western Europe have a long history of alcoholic “hard” cider production made from the fermented juice of apples (Malus spp.), especially in regions where cultivation of European grapevines (Vitis vinifera) for wine was climatically limited. While all apples contain fermentable sugars, in many regions, cultivars were selected, named, and propagated specifically for fermentation. This review highlights fruit quality attributes that are important for cider production and that are distinct from fresh‐market apple fruit and wine grapes. Polyphenol profiles, yeast assimilable nitrogen composition, carbohydrates, organic acids, pectin, and volatile aroma compounds are discussed as they relate to cider quality.

An apple long-chain acyl-CoA synthase, MdLACS1, enhances biotic and abiotic stress resistance in plants

Epidermal waxes are part of the outermost hydrophobic structures of apples and play a significant role in enhancing apple resistance and improving fruit quality. The biosynthetic precursors of epidermal waxes are very long-chain fatty acids (VLCFAs), which are made into different wax components through various wax synthesis pathways. In Arabidopsis thaliana, the AtLACS1 protein can activate the alkane synthesis pathway to produce very long-chain acyl CoAs (VLC-acyl-CoAs), which provide substrates for wax synthesis, from VLCFAs. The apple protein MdLACS1, encoded by the MdLACS1 gene, belongs to the AMP-binding superfamily and has long-chain acyl coenzyme A synthase activity, but its function in apple remains unclear. Here, we identified MdLACS1 in apple (Malus × domestica) and analyzed its function. Our results suggest that MdLACS1 promotes wax synthesis and improves biotic and abiotic stress tolerance, which were directly or indirectly dependent on wax. Our study further refines the molecular mechanism of wax biosynthesis in apples and elucidates the physiological function of wax in resistance to external stresses. These findings provide candidate genes for the synergistic enhancement of apple fruit quality and stress tolerance.

Application of Homemade Organic Fertilizer for Improving Quality of Apple Fruit, Soil Physicochemical Characteristics, and Microbial Diversity

Application of the organic fertilizers can improve soil properties and agricultural product quality, while the in-depth effect of organic fertilizer needs further exploration. In this study, the apple fruit (Malus pumila Mill.) quality, soil physicochemical characteristics, and microbial community under different fertilizers including control without fertilizer (CK), composted manure (CM), biogas slurry (BS), and chemical fertilizer (CF) were systematically investigated, and each treatment was repeated three times in completely random block plots with equal NPK content of fertilizer applied in each treatment. The CM treated apple fruit were observed with the best vertical diameter (78.72 ± 4.32 mm), transverse diameter (87.51 ± 1.3 mm), and color index (L* = 55.48 ± 5.48, b* = 18.96 ± 1.86). Meanwhile, the CM and BS treated apple fruit had higher flesh firmness than that of CK and CF treatment, implying that the organic fertilization can improve the storability and crispy taste apple fruit. Furthermore, the total sugars, essential amino acid, crude protein, total acids, and soluble solid contents of apple fruit were also significantly improved by using CM and BS fertilizer due to the resulting higher N, P, and organics content in soil. The application of organic fertilizer also dramatically enhanced the bacterial and fungi diversity, which may contribute to better soil respiration. The results obtained in this study reveals the insight effect of organic fertilizer on improvement of fruit quality and soil health and can supply technical assistance to organic cultivation of apple.

Impact of vanillin on postharvest disease control of apple.

Apple fruits are susceptible to infection by postharvest fungal pathogens, which may cause fruit decay and severe economic losses. This study investigated the antifungal spectrum of vanillin against common decay pathogens of apple and explored the antifungal mechanisms of vanillin in vitro. In vivo experiments were carried out to evaluate the effects of vanillin on apple postharvest disease control and fruit quality. Moreover, the induced resistance mechanism of vanillin on apple fruit was preliminarily explored. The results showed that vanillin has broad-spectrum antifungal effects, especially on Alternaria alternata. Vanillin could significantly inhibit the growth rate, mycelium biomass, and spore germination of pathogenic fungi by increasing the cell membrane permeability and lipid peroxidation. Importantly, vanillin treatment reduced the incidence of apple decay caused by A. alternata and Penicillium expansum, and contributed to improve fruit quality. Further studies indicated that vanillin could induce elevation in the activities of defense-related enzymes in apple fruit, such as phenylalanine ammonia-lyase (PAL), chitinase (CHI) and β-1,3-glucanase (β-1,3-GA), and increase total phenols and flavonoids contents. Generally, these results suggest that vanillin may contribute to the induced resistance of apple fruits to pathogenic fungi. To conclude, the results of this research provide theoretical foundations for the application of vanillin in the control of apple postharvest decay caused by fungal pathogens.

Convolutional Neural Networks for Estimating the Ripening State of Fuji Apples Using Visible and Near-Infrared Spectroscopy

The quality of fresh apple fruits is a major concern for consumers and manufacturers. Classification of these fruits according to their ripening stage is one of the most decisive factors in determining their quality. In this regard, the aim of this work is to develop a new method for non-destructive classification of the ripening state of Fuji apples using hyperspectral information in the visible and near-infrared (Vis/NIR) regions. Spectra of 172 apple samples in the range from 450 to 1000 nm were studied, which were selected from four different ripening stages. A convolutional neural network (CNN) model was proposed to perform the classification of the samples. The proposed method was compared with three alternative methods based on artificial neural networks (ANN), support vector machines (SVM), and k-nearest neighbors (KNN). The results revealed that the CNN method outperformed the alternative methods, achieving a correct classification rate (CCR) of 96.5%, compared with an average of 89.5%, 95.93%, and 91.68% for ANN, SVM, and KNN, respectively. These results will help in the development of a new device for fast and accurate estimation of the quality of apples.

Research Progress on Genetic Basis of Fruit Quality Traits in Apple (Malus × domestica).

Identifying the genetic variation characteristics of phenotypic traits is important for fruit tree breeding. During the long-term evolution of fruit trees, gene recombination and natural mutation have resulted in a high degree of heterozygosity. Apple (Malus × domestica Borkh.) shows strong ecological adaptability and is widely cultivated, and is among the most economically important fruit crops worldwide. However, the high level of heterozygosity and large genome of apple, in combination with its perennial life history and long juvenile phase, complicate investigation of the genetic basis of fruit quality traits. With continuing augmentation in the apple genomic resources available, in recent years important progress has been achieved in research on the genetic variation of fruit quality traits. This review focuses on summarizing recent genetic studies on apple fruit quality traits, including appearance, flavor, nutritional, ripening, and storage qualities. In addition, we discuss the mapping of quantitative trait loci, screening of molecular markers, and mining of major genes associated with fruit quality traits. The overall aim of this review is to provide valuable insights into the mechanisms of genetic variation and molecular breeding of important fruit quality traits in apple.

Monitoring Effects of Rootstock Genotype and Soil Treatment Strategy on Postharvest Fruit Quality in ‘Gala’ Apple

Production of high-quality tree fruit requires management of tree health and vigor during orchard establishment, especially with regard to soil-borne pathogens. Available strategies for the mitigation of soil-borne diseases include chemical fumigants, Brassicaceous seed meal (SM) soil treatments, and the use of disease-tolerant rootstock genotypes. It has been documented that superior disease suppression can be achieved using specific combinations of rootstock genotype and soil treatment that, in part, alter the soil microbiome. However, regardless of soil treatment strategy or rootstock genetics, sublethal levels of phytotoxic compounds are known to have negative effects on the reproductive output of plants. Yet the effects of SM amendments and the resultant restructuring of the soil microbiome on fruit quality are not well studied. Thus, our objective was to explore the effects of pathogen suppression strategies on at-harvest and postharvest fruit quality of ‘Gala’ apples (Malus domestica) by observing effects of both rootstock genetics [‘Malling 26’ (‘M.26’) vs. ‘Geneva 41’ (‘G.41’)] and soil treatment strategy (fumigation vs. SM). We observed that rootstock genotype generally appeared to have a stronger effect than soil treatment strategy on at-harvest fruit quality and postharvest outcomes. Further, although we did observe some fruit quality differences in each year of the study, there was no discernible pattern from year to year. We therefore conclude that, in our study, soil treatment does not have a consistent, significant influence on ‘Gala’ apple fruit quality, and importantly, efficacious ARD control using SM is without an apparent downside regarding fruit quality.

Effects of 1-methylcyclopropene treatment on fruit quality and antioxidant activities of ruby-S apples during cold storage

The effects of 1-methylcyclopropene (1-MCP) on the fruit quality and antioxidant activity of ruby-S apples were evaluated during cold storage. The fruits were treated with 0 (control) and 1 μL/L 1-MCP and stored at 0°C for six months. The assessments were performed at 0 (harvest), 3, and 6 months of storage. Compared with the control, the 1-MCP-treated fruits exhibited a reduced internal ethylene concentration and slowed appearance of greasiness on the fruit skin. In addition, 1-MCP treatment helped maintain a reduction in flesh firmness, titratable acidity, and peel color attributes (L* and b*) of the fruit. However, 1-MCP treatment did not affect fruit weight loss, soluble solids content, or peel color a* value. The 1-MCP treatment helped delay the reduction in total phenolics (TPC) and total flavonoids (TFC) content as well as total antioxidant determined by 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity (RSA) in the peel tissue. In the pulp tissue, 1-MCP affected only TPC, and not TFC or DPPH RSA. Overall, this study suggests that 1-MCP treatment helps maintain the desirable fruit quality attributes of ruby-S apples during ripening, but its effect on antioxidant activity depends on the tissue type (peel and pulp) of the fruit.

Control of Apple Fruit Rot Caused by Alternaria porri and Alternaria mali by Using Hot Water Treatment and Some Inorganic Salts

Apple rot is one of the most important apple diseases worldwide. The disease causes significant losses in both the quantity and quality of apple fruits. In this study, the antifungal activity of hot water treatment and salts were investigated against apple fruit rots caused by Alternaria porri and Alternaria mali. Linear growth of tested fungi was inhibited at 5ºC, however, growth was increased by increasing storage temperature degree from 15ºC to 25ºC and decreased at 35ºC. On the other hand, hot water treatment at 55ºC significantly reduced the decay index and severity of infection. When salts such as potassium bicarbonate (KCO3), calcium chloride (CaCl2), sodium bicarbonate (NaHCO3) and ammonium bicarbonate (NH4CO3) was applied, a significant reduction in linear growth and fruit rot incidence was noticed using potassium bicarbonate. Calcium chloride, ammonium bicarbonate and sodium bicarbonate greatly inhibited growth of A. porri and A. mali. The most effective inhibitor of fruit decay was potassium bicarbonate and calcium chloride.

Effects of water stress on quality and sugar metabolism in ‘Gala’ apple fruit

Sugar plays an important role in apple fruit development, appearance and quality as well as contributing to a plant's water stress response. Trehalose and the trehalose biosynthetic metabolic pathways are part of the sugar signaling system in plants, which are important regulator of water stress response in apple. The effect of water stress treatments applied to apple trees and the corresponding effects of ABA on developmental fruit quality were examined for indicators of fruit quality during fruit development. The results indicated that the severe water stress treatment (W2) occurring after the last stage of fruit cell division caused a decrease in the color and size of fruit. The moderate water stress (W1) occurring after the last stage of fruit cell enlargement (S2) caused an increase in the content of fructose and sorbitol while the apple fruit shape was not affected. These changes in sugar are related to the activity of sugar metabolic enzymes. While the enzymatic activity of vacuolar acid invertase (vAINV) was higher, that of sucrose-phosphate synthase (SPS) was lower in water stress treated fruit throughout the developmental period. This indicates that enhanced sucrose degradation and reduced sucrose synthesis leads to an overall reduced sucrose content during times of drought. Thus, water stress reduced sucrose content. Whereas the content of endogenous trehalose and ABA were the highest in water stress treated fruit. A moderate water stress (W1) imposed on apple trees via water restriction (60%–65% of field capacity) after the fruit cell enlargement phase of fruit development yielded sweeter fruit of higher economic value.

A balance between calcium and nitrate promotes the growth of M9T337 apple rootstocks

Unbalanced Calcium (Ca) and nitrogen (N) supply have been a struggle for apple fruit quality and yield. Calcium ion (Ca2+) and nitrate (NO3−) are two major forms of Ca and N absorbed by most terrestrial plants. The study was for investigating the effect of Ca2+ addition (5 and 10 mM) under different NO3− conditions (0, 5, 10, 15, 20, 25 mM) on M9T337 rootstocks phenotypes and their morphological, physiological, and related-genes differences in nutrient solution hydroponics. It was revealed from the study that independent variables significantly affected the plants growth. Relatively high NO3− plus less Ca2+ disturbed by different degrees of burned-down curling of rootstock leaves and root growth arrest. And Ca addition could relieve symptom caused by low and high N. The interaction of Ca and N increase their uptake by activating nitrate reductase (NR), glutamine synthetase (GS), Ca2+-ATPase and inducing CAM content, then up-regulating MdNRT1.1, MdNRT2.1, MdCDPK, and down-regulating MdACA expressions. Moreover, under lower-N (10 mM), moderate Ca (5 mM) could ensure optimal growth and development. And under higher-N (20 mM), more Ca (10 mM) was the most optimal, which was significantly different from other Ca2+ level (P˂0.05). Ultimately, maintaining a proper balance between N (0.01966-0.0303 kg kg−1) and Ca (0.0091-0.0141 kg kg−1) in leaves is important for developing desired apple rootstocks. Collectively, our data revealed that lower-N plus optimal Ca and higher-N plus more Ca could ensure better growth and improve their uptake efficiency, which would provide a scientific basis for rational fertilization and scientific management in extensive apple orchards.

Postharvest quality maintenance of wax apple and guava fruits by use of a fermented broth of an ε-poly-l-lysine-producing Streptomyces strain.

ε-Poly-l-lysine (ε-PL) is a natural antimicrobial polymer with significant inhibitory activity against a broad spectrum of microorganisms, and nowadays used widely as a preservative in the food industry. In the present study, ε-PL broth was obtained from Streptomyces ahygroscopicus GIM8 fermentation in a nutrient-limited liquid medium. The in vitro antifungal activity of the broth against fruit pathogens Penicillium expansum and Colletotrichum gloeosporioides was investigated, and its usage for postharvest storage of two highly perishable fruits wax apple and guava was evaluated. Results showed that ε-PL concentration in the broth reached 0.61 g/L, and the nutrition level of the broth was low. The antifungal activity of ε-PL broth was comparable to that of the aqueous solution of ε-PL under the same concentration. Immersion with the diluted broth (200 mg/L ε-PL) markedly delayed the decline in the quality of postharvest wax apple and guava fruits during storage, and the decay incidences were also greatly decreased as compared to their respective controls (distilled water immersion). A further investigation demonstrated that the ε-PL broth immersion induced an increase in the activity of defense-related enzymes peroxidase and polyphenol oxidase in the two fruits during storage. The present study proved that the fermentation broth of ε-PL could be used as a promising alternative to high purity ε-PL and synthetic fungicides for preserving fruits at postharvest stage.