Assuring Potato Tuber Quality during Storage: A Future Perspective

Effect of harvest-to-cooling delay and precooling on Kufri Jyoti (Solanum tuberosum) potato quality

Precooling is the rapid removal of field heat in harvested crops to preserve their quality and increase their shelf life. The following study was conducted to understand the importance of precooling and to optimize the precooling condition to extend the storage life of potatoes. Therefore, the study was divided into two components. In the first part, the Kufri Jyoti potatoes were subjected to field heat for 0-64 h, then were precooled for 48 h before sending to cold storage for 60 days. The results demonstrated that when the time delay was doubled, starch content (SC) decreased by 15.86%, reducing sugar content (RSC) increased by 32.71%, ascorbic acid content (AAC) decreased by 5.94% and total plate count (TPC) increased by 20.06%. Microstructural changes in potatoes due to the exposure to field heat were visible in SEM images. These results suggested a decrease in the quality of potatoes with an increase in time delay between harvest and cooling. In the second part of the study, the potatoes were precooled for 48 h at different temperatures (T) (6 °C, 8 °C, and 10 °C) and relative humidity (RH) (87%, 91%, and 95%), and their effect was studied on the same quality parameters after storage. Regression models were developed for each response, and models with non-significant lack of fit were selected for optimization. The analysis of the observations has shown that precooling aided in better quality retention of potatoes during cold storage.

Genotyping-by-sequencing targets genic regions and improves resolution of genome-wide association studies in autotetraploid potato

KEY MESSAGE

De novo genotyping in potato using methylation-sensitive GBS discovers SNPs largely confined to genic or gene-associated regions and displays enhanced effectiveness in estimating LD decay rates, population structure and detecting GWAS associations over 'fixed' SNP genotyping platform. Study also reports the genetic architectures including robust sequence-tagged marker-trait associations for sixteen important potato traits potentially carrying higher transferability across a wider range of germplasm. This study deploys recent advancements in polyploid analytical approaches to perform complex trait analyses in cultivated tetraploid potato. The study employs a 'fixed' SNP Infinium array platform and a 'flexible and open' genome complexity reduction-based sequencing method (GBS, genotyping-by-sequencing) to perform genome-wide association studies (GWAS) for several key potato traits including the assessment of population structure and linkage disequilibrium (LD) in the studied population. GBS SNPs discovered here were largely confined (~ 90%) to genic or gene-associated regions of the genome demonstrating the utility of using a methylation-sensitive restriction enzyme (PstI) for library construction. As compared to Infinium array SNPs, GBS SNPs displayed enhanced effectiveness in estimating LD decay rates and discriminating population subgroups. GWAS using a combined set of 30,363 SNPs identified 189 unique QTL marker-trait associations (QTL-MTAs) covering all studied traits. The majority of the QTL-MTAs were from GBS SNPs potentially illustrating the effectiveness of marker-dense de novo genotyping platforms in overcoming ascertainment bias and providing a more accurate correction for different levels of relatedness in GWAS models. GWAS also detected QTL 'hotspots' for several traits at previously known as well as newly identified genomic locations. Due to the current study exploiting genome-wide genotyping and de novo SNP discovery simultaneously on a large tetraploid panel representing a greater diversity of the cultivated potato gene pool, the reported sequence-tagged MTAs are likely to have higher transferability across a wider range of potato germplasm and increased utility for expediting genomics-assisted breeding for the several complex traits studied.

Climate Change Impacts on Potato Storage

In this study, we present a comprehensive literature review of the potential impacts of climate change on potato storage. Potato preservation can help reduce food loss and waste while increasing long-term food security, as potatoes are one of the most important crops worldwide. The review's results suggest climate change can negatively affect potato storage, especially tuber sprouting and diseases in storage chambers. Lower Sielianinov coefficient values (indicating dry and hot conditions) during the vegetative season of potato growing can lead to earlier sprouting. For instance, a decrease of 0.05 in the Sielianinov coefficient during the growing season results in tubers stored at 3 °C sprouting 25 days earlier and tubers stored at 5 °C experiencing a 15-day reduction in dormancy. This is due to the fact that the dry and hot climate conditions during the vegetation period of potato planting tend to shorten potato tubers' natural dormancy, which further leads to earlier sprouting during storage. Furthermore, high Sielianinov coefficient values may lead to worse disease situations. The results also suggest that research about the impacts of climate change on potato storage is very limited at the current stage, and further studies are needed to address the key knowledge gaps identified in this study.

Transcriptomic Analyses Reveal the Role of Cytokinin and the Nodal Stem in Microtuber Sprouting in Potato (Solanum tuberosum L.)

In potatoes, tuber secondary growth, especially sprouting, deforms the tubers and severely lowers their commercial value. Tuber sprouting is induced by signal substances, such as gibberellin (GA), which are transported to the tuber from the plant body. The molecular mechanism underlying GA-induced sprouting remains ambiguous. Here, we tried to recreate tuber secondary growth using in vitro stemmed microtubers (MTs) (with the nodal stem attached) and MT halves (with the nodal stem entirely removed). Our experiments showed that GA alone could initiate the sprouting of stemmed microtubers; however, GA failed to initiate MT halves unless 6-benzyladenine, a synthetic cytokinin CK, was co-applied. Here, we analyzed the transcriptional profiles of sprouting buds using these in vitro MTs. RNA-seq analysis revealed a downregulation of cytokinin-activated signaling but an upregulation of the "Zeatin biosynthesis" pathway, as shown by increased expression of CYP735A, CISZOG, and UGT85A1 in sprouting buds; additionally, the upregulation of genes, such as IAA15, IAA22, and SAUR50, associated with auxin-activated signaling and one abscisic acid (ABA) negative regulator, PLY4, plays a vital role during sprouting growth. Our findings indicate that the role of the nodal stem is synonymous with CK in sprouting growth, suggesting that CK signaling and homeostasis are critical to supporting GA-induced sprouting. To effectively control tuber sprouting, more effort is required to be devoted to these critical genes.

StBIN2 Positively Regulates Potato Formation through Hormone and Sugar Signaling

Potato is an important food crop worldwide. Brassinosteroids (BRs) are widely involved in plant growth and development, and BIN2 (brassinosteroid insensitive 2) is the negative regulator of their signal transduction. However, the function of BIN2 in the formation of potato tubers remains unclear. In this study, transgenic methods were used to regulate the expression level of StBIN2 in plants, and tuber related phenotypes were analyzed. The overexpression of StBIN2 significantly increased the number of potatoes formed per plant and the weight of potatoes in transgenic plants. In order to further explore the effect of StBIN2 on the formation of potato tubers, this study analyzed BRs, ABA hormone signal transduction, sucrose starch synthase activity, the expression levels of related genes, and interacting proteins. The results show that the overexpression of StBIN2 enhanced the downstream transmission of ABA signals. At the same time, the enzyme activity of the sugar transporter and the expression of synthetic genes were increased in potato plants overexpressing StBIN2, which also demonstrated the upregulation of sucrose and the expression of the starch synthesis gene. Apparently, StBIN2 affected the conversion and utilization of key substances such as glucose, sucrose, and starch in the process of potato formation so as to provide a material basis and energy preparation for forming potatoes. In addition, StBIN2 also promoted the expression of the tuber formation factors StSP6A and StS6K. Altogether, this investigation enriches the study on the mechanism through which StBIN2 regulates potato tuber formation and provides a theoretical basis for achieving a high and stable yield of potato.

New potential roles of StDREB1 and VvWRKY2 transcription factors in potato dormancy and sprouting patterns

In a previous study, transgenic potato plants overexpressing the StDREB1 or the VvWRKY2 transcription factor (TF) proved to have higher productivity and ameliorated tuber quality in comparison to wildtype (WT; the BF15 variety) plants. Interestingly, when stored at 4 °C, we noticed that the tubers of transgenic potato plants exhibited a delay in sprouting, hence a longer dormancy period. Therefore, we decided to study the dormancy and sprouting of these tubers (the two transgenic and the WT lines) through a physiological and biochemical characterization. WT and genetically modified (GM) tubers were stored at 4 °C for different periods (0, 30, 90, 180, and 240 days) followed by placing them in a germination chamber and the sprouting parameters were then monitored. According to our findings, the overexpression of these two TFs led to modifications in the sprouting kinetic of tubers through an extension of the dormancy period and changes in the sprouting process. Indeed, WT tubers emitted apical and lateral sprouts while those from GM plants showed mainly apical sprouts. In addition, higher reactive oxygen species (ROS) rates, indicators of tuber aging, were recorded in WT tubers compared to GM ones. The higher antioxidant enzyme activities in GM tubers seem to be responsible for aging modification in comparison to WT. The above results suggest the first report on new roles of the StDREB1 and VvWRKY2 TF which seemed to be involved in the regulation of potato tuber aging via a reduction of the main biochemical factors concentration and the ROS content leading to a longer dormancy period and a modified sprouting pattern.

Determination of the effect of abiotic stress on the oxidative potential of edible potato tubers

Stress factors occurring during the growing season and potato storage, can negatively affect the quality of tubers, including an increased tendency to enzymatic darkening. Abiotic stress due to water shortage is a major factor limiting agricultural production. The purpose of the study was to determine the effect of cultivation technology based on the use of biostimulant, hydrogel and irrigation as well as storage on the propensity to darkening and the content of sugars and organic acids. The results show that genotypic and technological variability in interaction with growing season conditions had a significant (p < 0.05) effect on the oxidative potential (OP) of potato tubers. The Denar cultivar, compared to the 'Gardena', was characterized by a lower tendency to enzymatic darkening. Application of biostimulant and hydrogel generally contributed to lowering the oxidative potential of the tested cultivars. The application of anti-stress agents had no effect on organic acid content. The long-term storage caused an increase in the content of total sugars (TS) (22%), reducing sugars (RS) (49%), chlorogenic acid (ACH) (11%), and loss of ascorbic acid (AA) (6%) in the tubers which contributed to an increase in the oxidative potential of potato tubers (16%). The correlation coefficients obtained (p < 0.05) confirm the dependence of OP on the concentration of organic acids.

Melissa officinalis L. as a Sprout Suppressor in Solanum tuberosum L. and an Alternative to Synthetic Pesticides

The goal of this research was to screen plant essential oils (EOs) as sprout inhibitors or suppressors in potato (Solanum tuberosum L.). Three controlled environment experiments were conducted to screen 18 EOs and several pure compounds as sprout inhibitors. The EOs were applied using the wicked method on potato cv. Gala in 19 L plastic containers. The results indicated that Melissa officinalis L. EO inhibited sprouting, while Coriandrum sativum L. seed oil and the EO blend of Lavandula angustifolia Mill. and Salvia sclarea L. suppressed sprouting. The EOs of interest were analyzed using gas chromatography coupled to mass spectrometry (GC-MS) and/or a flame ionization detector (GC-FID); the detailed chemical profiles are provided. The M. officinalis EO was fractionated into seven fractions, and these were tested on minitubers. We identified two fractions (F and A) that suppressed potato sprouting better than the whole oil. The GC-MS-FID analyses of M. officinalis EO fraction A identified myrcene, Z-ocimene, E-ocimene, trans-caryophyllene, and α-humulene as the main constituents, while the main constituents of fraction F were α-terpineol, β-citronellol, and geraniol. The pure isolated compounds, together with the major compound in M. officinalis EO (citral), were tested for sprout suppression on three potato cultivars (Ranger Russet, Terra Rosa, and Dakota TrailBlazer), which revealed that β-citronellol reduced the sprout length and the number of sprouts in all three cultivars, while citral and (+)-α-terpineol reduced the sprout length and the number of sprouts in Ranger Russet relative to the two controls in all three cultivars. Myrcene had a stimulating effect on the number of sprouts in Cv. Terra Rosa. However, none of the pure compounds suppressed sprouting completely or were comparable to the EO of M. officinalis.

The protein phosphatase 2A catalytic subunit StPP2Ac2b is involved in the control of potato tuber sprouting and source-sink balance in tubers and sprouts

Sprouting negatively affects the quality of stored potato tubers. Understanding the molecular mechanisms that control this process is important for the development of potato varieties with desired sprouting characteristics. Serine/threonine protein phosphatase type 2A (PP2A) has been implicated in several developmental programs and stress responses in plants. PP2A comprises a catalytic (PP2Ac), a scaffolding (A), and a regulatory (B) subunit. In cultivated potato, six PP2Ac isoforms were identified, named StPP2Ac1, 2a, 2b, 3, 4, and 5. In this study we evaluated the sprouting behavior of potato tubers overexpressing the catalytic subunit 2b (StPP2Ac2b-OE). The onset of sprouting and initial sprout elongation is significantly delayed in StPP2Ac2b-OE tubers; however, sprout growth is accelerated during the late stages of development, due to a high degree of branching. StPP2Ac2b-OE tubers also exhibit a pronounced loss of apical dominance. These developmental characteristics are accompanied by changes in carbohydrate metabolism and response to gibberellic acid, and a differential balance between abscisic acid, gibberellic acid, cytokinins, and auxin. Overexpression of StPP2Ac2b alters the source-sink balance, increasing the source capacity of the tuber, and the sink strength of the sprout to support its accelerated growth.

Physiological and proteomic analyses of γ-aminobutyric acid (GABA)-treated tubers reveals that StPOD42 promotes sprouting in potato

Gamma-aminobutyric acid (GABA) is a nonproteinogenic amino acid that plays vital roles in plant growth and developmental processes. However, its role in regulating potato sprouting is unknown. Therefore, the physiological and molecular mechanisms underlying the sprouting process were assessed, and we found that GABA promoted sprouting after treatment for 50 d. In addition, the GABA and soluble sugar contents increased while the starch content decreased. To study the molecular mechanism by which exogenous GABA accelerates tuber sprouting, comparative proteomic analysis of tuber bud eyes was performed after GABA treatment for 48 h. Further analysis revealed 316 differentially abundant proteins (DAPs) that are mainly involved in fatty acid and sugar metabolism and cutin, suberin and wax biosyntheses. The qRT‒PCR results suggested that the GABA transaminase 2 (GABA-T2) and GABA-T3 expression levels showed the greatest decrease at 30 d of storage. Peroxidase 42 (StPOD42) expression showed the greatest increase at 30 d. Overexpression of StPOD42 in potato was found to promote tuber sprouting. Our results provide new insights into the role of GABA in regulating the sprouting process and indicate that StPOD42 is a target gene for molecular breeding to modulate potato sprouting.

Comparing anatomy, chemical composition, and water permeability of suberized organs in five plant species: wax makes the difference

The efficiency of suberized plant/environment interfaces as transpiration barriers is not established by the suberin polymer but by the wax molecules sorbed to the suberin polymer. Suberized cell walls formed as barriers at the plant/soil or plant/atmosphere interface in various plant organs (soil-grown roots, aerial roots, tubers, and bark) were enzymatically isolated from five different plant species (Clivia miniata, Monstera deliciosa, Solanum tuberosum, Manihot esculenta, and Malus domestica). Anatomy, chemical composition and efficiency as transpiration barriers (water loss in m s^-1) of the different suberized cell wall samples were quantified. Results clearly indicated that there was no correlation between barrier properties of the suberized interfaces and the number of suberized cell layers, the amount of soluble wax and the amounts of suberin. Suberized interfaces of C. miniata roots, M. esculenta roots, and M. domestica bark periderms formed poor or hardly any transpiration barrier. Permeances varying between 1.1 and 5.1 × 10^-8 m s^-1 were very close to the permeance of water (7.4 × 10^-8 m s^-1) evaporating from a water/atmosphere interface. Suberized interfaces of aerial roots of M. deliciosa and tubers of S. tuberosum formed reasonable transpiration barriers with permeances varying between 7.4 × 10^-10 and 4.2 × 10^-9 m s^-1, which were similar to the upper range of permeances measured with isolated cuticles (about 10^-9 m s^-1). Upon wax extraction, permeances of M. deliciosa and S. tuberosum increased nearly tenfold, which proves the importance of wax establishing a transpiration barrier. Finally, highly opposite results obtained with M. esculenta and S. tuberosum periderms are discussed in relation to their agronomical importance for postharvest losses and tuber storage.

Sprout Suppressants in Potato Storage: Conventional Options and Promising Essential Oils—A Review

Potatoes are a staple in the diet of millions, and constant demand necessitates the storage of large quantities to meet year-round consumption. Potato sprouting during storage is a major problem that leads to lost revenue and food waste, inspiring numerous studies into methods of sprout suppression. As bans on common synthetic suppressants become increasingly widespread, greater attention is turning to organic alternatives including essential oils (EOs) as sprout suppressants. This review presents an overview of physical and chemical means of sprout suppression in stored potato and critically analyzes studies focusing on the use of EOs for sprout suppression. Promising EOs are identified and evaluated for use in fresh, processing, and seed potato storage. Challenges and limitations of EO use in potato sprout suppression are discussed as well as areas of future research.

Effects of essential oils on potato tuber sprouting at room temperature storage in Ethiopia

This study was conducted with the objective of finding alternative management options for potato tuber sprouting during storage. Essential oils from Croton macrostachyus, Eucalyptus globulus, Allium sativum, Cymbopogon citratus, Cymbopogon martini, Rosmarinus officinalis and Thymus schimperi were applied in completely randomized design using two quantities (1 and 2 ml) and three frequencies (1, 2, 3). Essential oils from Cymbopogon citratus and Thymus schimperi showed the lowest percentage of weight loss relative to control tubers for varieties Gudene (8.07%) and Jalene (13.34%), respectively. Essential oils were applied in the form of vapour inside wooden box for 24 h without direct contact with tubers. For both varieties, the potato tuber weight loss found to be minimized using 2 ml essential oils. Similarly, lowest percentage of weight loss at one, two and three applications were found for variety Jalene from Cymbopogon martini, Eucalyptus globulus and Croton macrostachyus, respectively. On the other hand, lowest percentage of weight loss was maintained using Eucalyptus globulus for variety Gudene. The number and length of sprouts did not vary with quantities. Therefore, for variety Gudene, lower number of sprouts relative to control tuber (3 sprouts/tuber) was found on potato tuber treated with essential oils from Cymbopogon martini and Thymus schimperi (2.7 sprouts/tuber) whereas for variety Jalene, lower number of sprouts relative to control tuber (8.7 sprouts/tubers) was found on potato tubers treated with essential oils from Allium sativum and Rosmarinus officinalis (5.7 sprouts/tuber). The length of the longest sprouts on control tubers was 11.7 mm and 20 mm for varieties Gudene and Jalene, respectively. Longest and shortest length of sprout was found on potato tubers treated with Eucalyptus globulus and Rosmarinus officinalis, respectively, for both varieties. Therefore, essential oils used in the current study are promising alternatives to control potato sprouting during storage. However, seedlings of these species and other potential species must be made available to farmers with training on how to make extracts and apply them.

Identification of volatile biomarkers for high-throughput sensing of soft rot and Pythium leak diseases in stored potatoes

Soft rot and Pythium leak are postharvest storage diseases of potato tubers that can cause substantial crop losses in the US. This study focused on detecting volatile organic compounds (VOCs) associated with rot inoculated tubers during storage (up to 21 days) using headspace solid-phase microextraction (SPME) coupled to gas chromatography (GC) with mass spectrometry (MS) and flame ionization detector (FID) analysis. Russet Burbank and Ranger Russet tubers were inoculated with the rot pathogens. Static sampling with 50 min trapping time followed by GC-MS and GC-FID analysis identified 23 and 30 common VOCs from the pathogen inoculated tubers. Overall, n,n-dimethylmethylamine, acetone, 1-undecene, and styrene, occurred frequently and repeatability in inoculated samples based on GC-MS analysis, with the latter two found using GC-FID analysis as well. Identification of such biomarkers can be useful in developing high-throughput VOC sensing systems for early disease detection in potato storage facilities.

Improving the Biocontrol Potential of Endophytic Bacteria Bacillus subtilis with Salicylic Acid against Phytophthora infestans-Caused Postharvest Potato Tuber Late Blight and Impact on Stored Tubers Quality

Potato (Solanum tuberosum L.) tubers are a highly important food crop in many countries due to their nutritional value and health-promoting properties. Postharvest disease caused by Phytophthora infestans leads to the significant decay of stored potatoes. The main objective of this study was to evaluate the effects of the endophytic bacteria, Bacillus subtilis (strain 10–4), or its combination with salicylic acid (SA), on some resistance and quality traits of stored Ph. infestans-infected potato tubers. The experiments were conducted using hydroponically grown potato mini-tubers, infected prior to storage with Ph. infestans, and then coated with B. subtilis, alone and in combination with SA, which were then stored for six months. The results revealed that infection with Ph. infestans significantly increased tuber late blight incidence (up to 90–100%) and oxidative and osmotic damage (i.e., malondialdehyde and proline) in tubers. These phenomena were accompanied by a decrease in starch, reducing sugars (RS), and total dry matter (TDM) contents and an increase in amylase (AMY) activity. Moreover, total glycoalkaloids (GA) (α-solanine, α-chaconine) notably increased in infected tubers, exceeding (by 1.6 times) permissible safe levels (200 mg/kg FW). Treatments with B. subtilis or its combination with SA decreased Ph. infestans-activated tuber late blight incidence (by 30–40%) and reduced oxidative and osmotic damages (i.e., malondialdehyde and proline) and AMY activity in stored, infected tubers. Additionally, these treatments decreased pathogen-activated GA accumulation and increased ascorbic acid in stored tubers. Thus, the results indicated that endophytic bacteria B. subtilis, individually, and especially in combination with SA, have the potential to increase potato postharvest resistance to late blight and improve tuber quality in long-term storage.

Rapid Estimation of Potato Quality Parameters by a Portable Near-Infrared Spectroscopy Device

The aim of the present work was to determine the main quality parameters on tuber potato using a portable near-infrared spectroscopy device (MicroNIR). Potato tubers protected by the Protected Geographical Indication (PGI “Patata de Galicia”, Spain) were analyzed both using chemical methods of reference and also using the NIR methodology for the determination of important parameters for tuber commercialization, such as dry matter and reducing sugars. MicroNIR technology allows for the attainment/estimation of dry matter and reducing sugars in the warehouses by directly measuring the tubers without a chemical treatment and destruction of samples. The principal component analysis and modified partial least squares regression method were used to develop the NIR calibration model. The best determination coefficients obtained for dry matter and reducing sugars were of 0.72 and 0.55, respectively, and with acceptable standard errors of cross-validation. Near-infrared spectroscopy was established as an effective tool to obtain prediction equations of these potato quality parameters. At the same time, the efficiency of portable devices for taking instantaneous measurements of crucial quality parameters is useful for potato processors.

Evaluating Ecologically Acceptable Sprout Suppressants for Enhancing Dormancy and Potato Storability: A Review

Postharvest losses are a key stumbling block to long-term postharvest storage of potato tubers. Due to the high costs and lack of infrastructure associated with cold storage, this storage method is often not the most viable option. Hence, sprout suppressants are an appealing option. In most developing countries, potato tubers in postharvest storage are accompanied by a rapid decline in the potato tuber quality due to the physiological process of sprouting. It results in weight changes, increased respiration, and decreased nutritional quality. Therefore, proper management of sprouting is critical in potato storage. To avoid tuber sprouting, increased storage and transportation of potatoes demands either the retention of their dormant state or the application of sprout growth suppressants. This review evaluates the current understanding of the efficacy of different sprout suppressants on potato storability and the extension of potato shelf-life. We also consider the implications of varied study parameters, i.e., cultivar, temperature, and method of application, on the outcomes of sprout suppressant efficacies and how these limit the integration of efficient sprout suppression protocols.

High-Pressure Processing on Whole and Peeled Potatoes: Influence on Polyphenol Oxidase, Antioxidants, and Glycaemic Indices

Polyphenol oxidase (PPO) inactivation in five whole and peeled Irish potato cultivars was investigated using high-pressure processing (HPP) at 400 MPa and 600 MPa for 3 min. PPO activity was significantly lower in most of the HPP-treated samples, while the highest PPO inactivation was observed after HPP at 600 MPa. No significant (p > 0.05) changes were observed on the total phenolic content and antioxidant activity of all the HPP-treated potatoes. Regarding individual phenolic acids, chlorogenic acid was decreased significantly (p < 0.05) in all studied varieties with a concomitant increase (p < 0.05) in caffeic and quinic acid. Similarly, ferulic acid was also increased (p < 0.05) in all studied varieties after the HPP treatment, while there was a variation in rutin and 4-coumaric acid levels depending on the cultivar and the sample type. Anthocyanins in the coloured whole potato varieties (i.e., Kerr’s Pink and Rooster), tentatively identified as pelargonidin-O-ferulorylrutinoside-O-hexoside and pelargonidin-O-rutinoside-O-hexoside, also exhibited significantly (p < 0.05) higher levels in the HPP-treated samples as opposed to those untreated. Glycaemic indices of the potatoes treated with HPP did not differ with the corresponding untreated cultivars.

Maleic and L-tartaric acids as new anti-sprouting agents for potatoes during storage in comparison to other efficient sprout suppressants

Inhibiting sprouting of potatoes is an interesting subject needed for potato storage and industry. Sprouting degrades the quality of tuber along with releasing α-solanine and α-chaconine, which are harmful for health. Sprout suppressants, available in the market, are either costly or toxic to both health and environment. So, there is a need for developing countries to explore new sprouting suppressant compound which is cheap, non-toxic and reasonably efficient in comparison to commercial ones. We have established that simple maleic acid and L-tartaric acid are effective sprout suppressing agents. Both can hinder sprouting up to 6 weeks and 4 weeks post treatment respectively at room temperature in dark. These do not affect the quality parameters, retain the moisture content and maintain the stout appearance of the tubers along the total storage period. Thus maleic acid and L-tartaric acid would qualify as alternative, cheap, efficient sprout suppressant for potato storage and processing.

Combining conventional QTL analysis and whole-exome capture-based bulk-segregant analysis provides new genetic insights into tuber sprout elongation and dormancy release in a diploid potato population

Tuber dormancy and sprouting are commercially important potato traits as long-term tuber storage is necessary to ensure year-round availability. Premature dormancy release and sprout growth in tubers during storage can result in a significant deterioration in product quality. In addition, the main chemical sprout suppressant chlorpropham has been withdrawn in Europe, necessitating alternative approaches for controlling sprouting. Breeding potato cultivars with longer dormancy and slower sprout growth is a desirable goal, although this must be tempered by the needs of the seed potato industry, where dormancy break and sprout vigour are required for rapid emergence. We have performed a detailed genetic analysis of tuber sprout growth using a diploid potato population derived from two highly heterozygous parents. A dual approach employing conventional QTL analysis allied to a combined bulk-segregant analysis (BSA) using a novel potato whole-exome capture (WEC) platform was evaluated. Tubers were assessed for sprout growth in storage at six time-points over two consecutive growing seasons. Genetic analysis revealed the presence of main QTL on five chromosomes, several of which were consistent across two growing seasons. In addition, phenotypic bulks displaying extreme sprout growth phenotypes were subjected to WEC sequencing for performing BSA. The combined BSA and WEC approach corroborated QTL locations and served to narrow the associated genomic regions, while also identifying new QTL for further investigation. Overall, our findings reveal a very complex genetic architecture for tuber sprouting and sprout growth, which has implications both for potato and other root, bulb and tuber crops where long-term storage is essential.

New insights into the effects of ethylene on ABA catabolism, sweetening and dormancy in stored potato tubers

Continuous ethylene supplementation suppresses postharvest sprouting, but it can increase reducing sugars, limiting its use as an alternative to chlorpropham for processing potatoes. To elucidate the mechanisms involved, tubers were treated after curing with or without the ethylene binding inhibitor 1-methylcyclopropene (1-MCP at 1 μL L^-1 for 24 h), and then stored in air or air supplemented with continuous ethylene (10 μL L^-1). Across three consecutive seasons, changes in tuber physiology were assessed alongside transcriptomic and metabolomic analysis. Exogenous ethylene alone consistently induced a respiratory rise and the accumulation of undesirable reducing sugars. The transient respiratory peak was preceded by the strong upregulation of two genes encoding 1-aminocyclopropane-1-carboxylate oxidase (ACO), typical of wound and stress induced ethylene production. Profiles of parenchymatic tissue highlighted that ethylene triggered abscisic acid (ABA) catabolism, evidenced by a steep fall in ABA levels and a transient rise in the catabolite phaseic acid, accompanied by upregulation of transcripts encoding an ABA 8'-hydroxylase. Moreover, analysis of non-structural carbohydrate-related genes revealed that ethylene strongly downregulated the expression of the Kunitz-type invertase inhibitor, already known to be involved in cold-induced sweetening. All these ethylene-induced effects were negated by 1-MCP with one notable exception: 1-MCP enhanced the sprout suppressing effect of ethylene whilst preventing ethylene-induced sweetening. This study supports the conclusions that: i) tubers adapt to ethylene by regulating conserved pathways (e.g. ABA catabolism); ii) ethylene-induced sweetening acts independently from sprout suppression, and is similar to cold-induced sugar accumulation.

The Cysteine-Rich Peptide Snakin-2 Negatively Regulates Tubers Sprouting through Modulating Lignin Biosynthesis and H2O2 Accumulation in Potato

Potato tuber dormancy is critical for the post-harvest quality. Snakin/Gibberellic Acid Stimulated in Arabidopsis (GASA) family genes are involved in the plants’ defense against pathogens and in growth and development, but the effect of Snakin-2 (SN2) on tuber dormancy and sprouting is largely unknown. In this study, a transgenic approach was applied to manipulate the expression level of SN2 in tubers, and it demonstrated that StSN2 significantly controlled tuber sprouting, and silencing StSN2 resulted in a release of dormancy and overexpressing tubers showed a longer dormant period than that of the control. Further analyses revealed that the decrease expression level accelerated skin cracking and water loss. Metabolite analyses revealed that StSN2 significantly down-regulated the accumulation of lignin precursors in the periderm, and the change of lignin content was documented, a finding which was consistent with the precursors’ level. Subsequently, proteomics found that cinnamyl alcohol dehydrogenase (CAD), caffeic acid O-methyltransferase (COMT) and peroxidase (Prx), the key proteins for lignin synthesis, were significantly up-regulated in silencing lines, and gene expression and enzyme activity analyses also supported this effect. Interestingly, we found that StSN2 physically interacts with three peroxidases catalyzing the oxidation and polymerization of lignin. In addition, SN2 altered the hydrogen peroxide (H₂O₂) content and the activities of superoxide dismutase (SOD) and catalase (CAT). These results suggest that StSN2 negatively regulates lignin biosynthesis and H₂O₂ accumulation, and ultimately inhibits the sprouting of potato tubers.

Pre- and postharvest measures used to control decay and mycotoxigenic fungi in potato (Solanum tuberosum L.) during storage

Potato (Solanum tuberosum L.), a worldwide, staple food crop, is susceptible to postharvest rots caused by a variety of fungal pathogens, including Fusarium spp., Alternaria spp., Phytophthora infestans, Helminthosporium solani, Rhizoctonia solani, and Colletotrichum coccodes. Rots resulting from infections by these pathogens cause a significant reduction in potato quality and marketable yield. Importantly, some of these decay fungi also produce mycotoxins that represent a potential risk to human health. In the present review, an overview and discussion are provided on the epidemiology and pathogenesis of decay fungi, especially Fusarium spp., that include recent data derived from genomic and phylogenetic analyses. The biosynthesis and functional role of fungitoxic metabolites such as trichothecene mycotoxins and fusaric acid, produced in rotted potatoes are also reviewed. Advances in pre- and postharvest measures for rot management, especially eco-friendly methods including physical control, biological control, the use of natural compounds, and other agricultural management practices are also reviewed. Lastly, novel approaches to control potato dry rot such as the use of mycoviruses and CRISPR technology are highlighted.

Potato tuber metabolomics-based prediction of chip color quality and application using gas chromatography/flame ionization detector

Potato (Solanum tuberosum L.) tubers are usually harvested once a year; thus, long-term storage is required to supply quality-assured tubers throughout the year. Further, an applicable method to predict tuber quality during storage is needed. In this study, gas chromatography-mass spectrometry (GC/MS) metabolomics was applied to identify applicable biomarkers for prediction of potato chip color based on 3 years' field-grown tubers. The projections to latent structures (PLS) prediction model, calculated from a metabolome data set obtained before storage, was consistent with actual measured chip color values. Additionally, GC with frame ionization detector (GC/FID) metabolite fingerprinting simultaneously re-constructed more reliable and relevant prediction models for chip color quality compared to GC/MS. Moreover, nine metabolites detected by GC/MS analysis were further validated as applicable prediction markers. This strategy will provide a practical and cost-effective quality-control tool for potato processing manufacturers on an industrial scale.

Quantitative phosphoproteomics analysis reveals that protein modification and sugar metabolism contribute to sprouting in potato after BR treatment

Brassinosteroids (BRs), a new class of steroid hormones, are involved in the regulation of plant cell elongation and seed germination. Nevertheless, the molecular mechanism of the effect of BRs on tuber sprouting remains largely unknown. In this study, quantitative phosphoproteomics was employed to investigate the protein phosphorylation changes in sprouting induced by BRs. Our results showed that BRs accelerated the conversion of starch into soluble sugar in tubers. A functional enrichment cluster analysis suggested that the "amino acid metabolism pathway" was upregulated and that "plant hormone signal transduction and protein export" were downregulated. BR treatment also changed the phosphorylation of proteins involved in the BR, ABA, starch and sugar signal transduction pathways, such as serine/threonine-protein kinase (BSK), 14-3-3, alpha-glucan water dikinase (GWD), sucrose-phosphate synthase (SPS), sucrose synthase (SS) and alkaline/neutral invertase (A/N-INV). These results shed more light on the pattern of protein phosphorylation in BR promoting potato sprouting.

Effects of Endophytic Bacillus Subtilis and Salicylic Acid on Postharvest Diseases (Phytophthora infestans, Fusarium oxysporum) Development in Stored Potato Tubers

Postharvest diseases of potato lead to significant food and economic losses worldwide. The exogenous application of eco-friendly methods plays an important role in the control of postharvest decay. In this work the effects of endophytic bacteria B. subtilis (10-4, 26D) were studied in the context of two application parameters: concentration, with a range between 10³–10⁸ CFU/mL tested, and synergistic effects of the signal molecule salicylic acid (SA) (0.05 mM) on potato tubers’ resistance to Phytophthora infestans and Fusarium oxysporum during storage. The experiments were carried out on hydroponically grown potato (Solanum tuberosum L.) mini-tubers. This study demonstrates the suppressive effect of B. subtilis (10-4, 26D) on diseases of potato during storage and reveals that this effect happens in a dose-dependent manner, both individually and in combination with SA. The most effective concentrations of B. subtilis for suppression of both Ph.infestans and F. oxysporum are 10⁸ CFU/mL (10-4 and 26D), 10⁷ CFU/mL (10-4 + SA) and 10⁶ CFU/mL (26D + SA). The ability of B. subtilis (10-4, 26D) to effectively penetrate and colonize the internal tubers’ tissues when applied immediately prior to storage, and the ability of SA to accelerate these processes, have been proven. B. subtilis (10-4, 26D), individually and in compositions with SA, increased ascorbic acid content and decreased pathogen-induced proline accumulation and lipid peroxidation in tubers. This indicates a protective effect conferred to cells against reactive oxygen and an extension of aging processes, manifested by a prolonged shelf life and extended preservation of fresh appearance.

Silencing of α-amylase StAmy23 in potato tuber leads to delayed sprouting

Potato tuber dormancy is critical for the postharvest quality. The supply of carbohydrates is considered as one of the important factors controlling the rate of potato tuber sprouting. Starch is the major carbohydrate reserve in potato tuber, but very little is known about the specific starch degrading enzymes responsible for controlling tuber dormancy and sprouting. In this study, we demonstrate that an α-amylase gene StAmy23 is involved in starch breakdown and regulation of tuber dormancy. Silencing of StAmy23 delayed tuber sprouting by one to two weeks compared with the control. This phenotype is accompanied by reduced levels of reducing sugars and elevated levels of malto-oligosaccharides in tuber cortex and pith tissue below the bud eye of StAmy23-deficient potato tubers. Changes in soluble sugars is accompanied by a slight variation of phytoglycogen structure and starch granule size. Our results suggest that StAmy23 may stimulate sprouting by hydrolyzing soluble phytoglycogen to ensure supply of sugars during tuber dormancy.

A member of the TERMINAL FLOWER 1/CENTRORADIALIS gene family controls sprout growth in potato tubers

Potato tuber bud dormancy break followed by premature sprouting is a major commercial problem which results in quality losses and decreased tuber marketability. An approach to controlling premature tuber sprouting is to develop potato cultivars with a longer dormancy period and/or reduced rate of sprout growth. Our recent studies using a potato diploid population have identified several quantitative trait loci (QTLs) that are associated with tuber sprout growth. In the current study, we aim to characterize a candidate gene associated with one of the largest effect QTLs for rapid tuber sprout growth on potato chromosome 3. Underlying this QTL is a gene encoding a TERMINAL FLOWER 1/CENTRORADIALIS homologue (PGSC0003DMG400014322). Here, we use a transgenic approach to manipulate the expression level of the CEN family member in a potato tetraploid genotype (cv. Désirée). We demonstrate a clear effect of manipulation of StCEN expression, with decreased expression levels associated with an increased rate of sprout growth, and overexpressing lines showing a lower rate of sprout growth than controls. Associated with different levels of StCEN expression were different levels of abscisic acid and cytokinins, implying a role in controlling the levels of plant growth regulators in the apical meristem.

Application of essential oils as a natural and alternate method for inhibiting and inducing the sprouting of potato tubers

Use of harmful chemicals and expensive maintenance of cold-storage conditions for controlling sprouting are among the major problems in potato storage. Here, 20 essential oils (EOs) were tested for their sprouting-inhibiting and sprouting-inducing activities. Overall, treatments of lemon grass (LG) and clove (CL) oils could induce sprouting whereas palmarosa (PR) and ajwain (AZ) oils could inhibit sprouting of potato tubers at normal-room-temperature (25 ± 2 °C) storage. Selected-EOs treatments affected sprouting by modulation of accumulation of reducing sugars, ethylene, and expression of genes involved in tuber-sprouting such as ARF, ARP, AIP and ERF. Surprisingly, 7-days AZ-treatments could inhibit sprouting for 30-days which was mediated via damaging apical meristem. However, LG- and CL-treated tubers could produce enhanced potato yield as well. Present work clearly demonstrates that selected-EOs can be used as a promising eco-friendly approach for inducing/inhibiting sprouting of potato tubers during potato storage and those enhancing sprouting can be used for enhancing productivity.

Starchy Carbohydrates in a Healthy Diet: The Role of the Humble Potato

Potatoes have been an affordable, staple part of the diet for many hundreds of years. Recently however, there has been a decline in consumption, perhaps influenced by erroneous reports of being an unhealthy food. This review provides an overview of the nutritional value of potatoes and examines the evidence for associations between potato consumption and non-communicable diseases. Potatoes are an important source of micronutrients, such as vitamin C, vitamin B6, potassium, folate, and iron and contribute a significant amount of fibre to the diet. However, nutrient content is affected by cooking method; boiling causes leaching of water-soluble nutrients, whereas frying can increase the resistant starch content of the cooked potato. Epidemiological studies have reported associations between potato intake and obesity, type 2 diabetes and cardiovascular disease. However, results are contradictory and confounded by lack of detail on cooking methods. Indeed, potatoes have been reported to be more satiating than other starchy carbohydrates, such as pasta and rice, which may aid weight maintenance. Future research should consider cooking methods in the study design in order to reduce confounding factors and further explore the health impact of this food.