Chemical control of bacterial soft-rot of wounded potato tubers

Summary Five chemicals were applied to batches of wounded potato tubers by dipping in 1.5 g litre solutions for 1 min. After incubation for 10 days at 15 C under damp anaerobic conditions the amount of bacterial soft rotting was assessed. 5-nitro-8-hydroxyquinoline was the most effective in reducing rotting but 8-hydroxyquinoline, SD740823AX and chlorine dioxide also gave some control. Elbadyne had no significant effect. The results of tests in vitro were in broad agreement with those of tests in vivo for 5-nitro-8-hydroxyquinoline, 8-hydroxyquinoline and SD740823AX, but not Elbadyne and chlorine dioxide. The feasibility of controlling soft rotting by chemicals is demonstrated and screening procedures are discussed.     

Comparison of polyphenol oxidase in tubers ofSolanum tuberosum and the non-browning tubers ofS. hjertingii

Solarium hjertingii, a wild potato species, does not exhibit enzymatic browning nor blackspot. Blackspot and enzymatic browning are physiological disorders that are caused by the reaction of the enzyme polyphenol oxidase with phenolic substrates, resulting in discoloration of tuber cortex. We determined thatS. hjertingii has a low amount of at least one of the polyphenol oxidases in its tubers compared toS. tuberosum. Less than 5 μg ofS. tuberosum polyphenol oxidase protein, as determined from Western blot staining, had measurable enzymatic activity. In contrast,S. hjertingii protein with comparable staining had no detectable activity.     

Wound-induced suberization and periderm development in potato tubers as affected by temperature and gamma irradiation

Summary Histochemical evaluation of the wound-induced suberization and periderm formation, the processes of wound healing, in potato tubers (Solanum tuberosum L.) showed that both the processes occur most rapidly at 25°C. Wound-healing is delayed at 10 or 15°C while a temperature of 35°C prevented periderm formation and retarded suberization. Gamma irradiation up to 100 Gy, the optimal dose for sprout inhibition, did not affect suberization, which suggests that the DNA-replicating mechanism is more radiation-sensitive than suberin biosynthesis. A dose of 20 to 30 Gy, which had no effect on sprouting inhibited wound periderm formation indicating that meristems in resting buds are apparently less sensitive to irradiation than nuclei of the potential periderm cells. It seems probable that a major cause for the bacterial soft rot occurring in tubers when stored under high tropical ambient temperatures or when irradiated for sprout inhibition is due to an impairment of the wound periderm formation.

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Zusammenfassung Um die m?glichen Gründe für den gesteigerten mikrobiellen Abbau von Kartoffeln w?hrend der Lagerung unter tropischen Umweltbedingungen oder nach der Bestrahlung mit R?ntgenstrahlen zur Keimhemmung aufzukl?ren, wurde der Einfluss von Temperatur und Bestrahlung auf die durch Verletzung induzierte Suberin-und Peridermentwicklung untersucht. Es zeigte sich, dass sowohl die Suberinisierung als auch die Peridermentwicklung bei 25°C schneller verlaufen, w?hrend sie bei 10–15°C verlangsamt sind. Temperaturen über 35°C verhindern die Peridermbildung und verz?gern die Suberinisierung (Tabelle 1). Das Ausmass der Polyphenolbildung war im 1 mm unter der Verletzung bei 20, 25 und 28–30°C ?hnlich der bei 10°C und 15°C w?hrend es bei 35°C verringert war (Abb. 2). Histochemische Untersuchungen zeigten, dass die Suberinisierung in unbestrahlten Knollen und in Knollen, die bis zu 100 Gy erhalten hatten, der optimalen Dosis für die Keimhemmung, im gleichen Ausmass erfolgte (Tabelle 2). Aus diesen Ergebnissen wird geschlossen, dass der Verdopplungsmechanismus der DNS auf Bestrahlung empfindlicher reagiert als die Suberinsynthese. Der Gehalt an Polyphenolen in den suberinisierten Zellschichten war in bestrahlten Knollen vergleichsweise h?her (Tabelle 3). 20–30 Gy an R?ntgenstrahlen reichten aus, um die Wundperidermbildung zu unterbinden (Tabelle 2 und Abb. 1), w?hrend für die Keimhemmung eine Minimaldosis von 50 Gy ben?tigt wurde. Das bedeutet, dass die Meristeme in den ruhenden Knospen auf die Bestrahlung weniger empfindlich reagieren als die Kerne in den potentiellen Peridermzellen. Die suberinisierten Zellschichten k?nnen von der Wundoberfl?che unbestrahlter Knollenh?lften leicht abgeschoben werden, w?hrend das bei Knollen, die einer Bestrahlung von 20 Gy und mehr ausgesetzt waren, nicht m?glich ist. Dieser Unterschied k?nnte als Methode zur Identifizierung bestrahlter Knollen verwendet werden. Die Ergebnisse zeigen, dass die Sch?digung der Wundperidermentwicklung ein Hauptgrund für die gesteigerte mikrobielle F?ule von Kartoffelknollen w?hrend der Lagerung bei tropischen Temperaturen oder nach Bestrahlung zur Keimhemmung ist.

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Résumé L'influence de la température et de l'irradiation sur la subérisation d'une blessure occasionnée et sur le développement du périderme a été étudiée, dans le but d'expliquer les déchets de pourritures microbiennes sur des tubercules mis en conservation sous des conditions de climat tropical ou à la suite d'une exposition aux rayons gamma en vue de l'inhibition de la germination. Le développement du périderme et la subérisation se sont effectués rapidement à 25°C mais les réactions ont été retardées à 10 ou 15°C. Une température de 35°C a empêché la formation de périderme et retardé la subérisation (tableau 1). Le taux de polyphénol dans la 1ère couche d'1 mm sous la blessure était sensiblement le même à 10, 15, 20, 25 et 28–30°C mais il avait diminué à 35°C (figure 2). Les résultats de l'analyse hystochimique ont montré que la subérisation avait progressé à vitesse égale pour des tubercules non-irradiés et des tubercules irradiés à plus de 100 Gy, dose optimale correspondant à l'inhibition de la germination. Ces résultats suggèrent que le mécanisme de réplication de l'ADN est plus sensible à la radiation que la biosynthèse de la subérine. Le niveau de polyphénols dans les couches cellulaires en voie de subérisation était plus élevé dans les tubercules irradiés que dans les tubercules non irradiés (tableau 3). 20 à 30 Gy de rayons gamma ont suffi pour empêcher la formation du périderme de cicatrisation (tableau 2 et figure 1) tandis que la dose minimale nécessaire à l'inhibition de la germination était de 50 Gy. Les méristèmes de germes en dormance seraient donc moins sensibles à l'irradiation que les noyaux des cellules du périderme potentiel. Les couches cellulaires subérisées peuvent facilement se détacher de la surface endommagée lorsqu'il s'agit de tubercules non irradiés, tandis qu'elles sont difficilement séparables dans le cas de tubercules exposés à 20 Gy ou plus. Cette différence peut conduire à une méthode d'identification des tubercules irradiés. La recrudescence des pourritures microbiennes sur tubercules mis en conservation à des températures tropicales ou exposés aux rayons gamma en vue d'inhibition de la germination, semble liée principalement au ralentisement du développement d'un périderme de cicatrisation.

     

Sucrose accumulation during high-temperature storage of potato tubers

Summary Potato tubers stored in a farm store from April to October (monthly average temperature between 24.7 and 36.2°C) accumulated considerable quantities of total sugars. Sucrose was the main component though in the variety Kufri Chandramukhi reducing sugars accumulated in amounts equal to sucrose.     

Alpha-amylase inhibitor changes during processing of sweet potato and taro tubers

Alpha-amylase inhibitor changes during processing ofsweet potatoes (Ipomoea batatas) and taro (Colocasia esculenta)indicated that varietal differences profoundly influence the thermalinactivation profile. The -amylase inhibitors of taro were almosttotally inactivated during oven drying of the chips at 90 ^°C and100 ^°C for 24h, while 0.8–10% activity was retained in sweetpotato chips under the same conditions. Relatively better thermal stabilitywas exhibited by the sweet potato amylase inhibitors at lower temperatures(70 and 80 ^deg;C) as well. Cooking by boiling the tuber pieces inwater resulted in retention of 29–59% amylase inhibitor in sweet potatoand 11–16% in taro. Microwave baking was a better method forinactivation of amylase inhibitors in these tubers. Flour prepared from thetubers retained only trivial amounts of the inhibitor.     

Distribution of oxidase enzymes in potato tubers relative to blackspot susceptibility. I. Phenolases

To determine whether phenolase activity is related to susceptibility or resistance to blackspot, tissue from bud and stem ends of potato tubers was assayed for differences in monophenolase and polyphenolase activities, changes in activity due to bruising, and different forms of phenolase. No relationship between blackspot and phenolase activity was found when activities of selected tissue were determined with p-cresol, tyrosine or chlorogenic acid as substrates. A significant positive relationship was found between polyphenolase activity and blackspot susceptibility when total or soluble or particulate fractions of phenolase activity were determined with catechol. Stem tissue had a significantly higher rate of phenolase activity than did bud-end tissue, where activity was determined with p-cresol, tyrosine or catechol; no significant differences in activity between the ends were found when chlorogenic acid was used.     

Increase in phosphorylase activity during cold-induced sugar accumulation in potato tubers

Summary The accumulation of reducing sugars, sucrose and hexose phosphates in cv. Bintje and genotype KW77-2916 during storage at 2, 4, or 8°C was studied in relation to several catalytic activities. Bintje tubers accumulated sugars during storage at 2 or 4°C, whereas KW77-2916 showed reduced cold-sweetening at 2°C. The increase in glucose 6-phosphate and sucrose occurred concurrently and preceded the increase in reducing sugar concentration. Phosphorylase activity showed a strong interaction with temperature, storage duration and sugar accumulation in both genotypes. Invertase activity increased in Bintje concomitantly with the increase in reducing sugars, but this effect was less obvious in KW77-2916. The activities of other glycolytic and Krebs cycle enzymes showed no obvious correlation with sugar accumulation. It is suggested that the increase in phosphorylase activity acts as a triggering event in the sweetening of potato tubers during cold storage.     

Surface area estimation of potato tubers

Summary Surface areas of tubers of the potato cultivars Cara, Désirée, King Edward and Maris Piper were estimated empirically by measuring the area of adhesive tape required to cover each tuber surface. Measuring the area of thin peelings of all four cultivars underestimated tuber surface area, the degree of underestimation increasing with decreasing tuber size. ‘Shape factors’ (D), calculated as:D = surface area/volume^2/3, varied with tuber size and variety (overall mean = 5.070±0.0245;n=56), but would be suitable for estimating the surface areas of similarly-sized tubers of a single cultivar. A mathematical model which used a surface integral to estimate a tuber's surface area from its axial dimensions and volume closely approximated to the empirical estimates of surface area for all four cultivars, and would be preferable to the use of shape factors when estimating surface areas of potatoes with variable shapes or unknownD values.

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Zusammenfassung Es wurden verschiedene Methoden zur Sch?tzung der Oberfl?chengr?sse an Knollen der Kartoffelsorten Cara, Désirée, King Edward und Maris Piper verglichen. Die Knollenform war abh?ngig von Sorte und Gr?sse (Abb. 1A). Empirische Sch?tzungen der Oberfl?chengr?sse erhielt man, in dem mit Hilfe eines transportablen Fl?chenmeters der Fl?cheninhalt eines undurchsichtigen Klebebandes bestimmt wurde, das in dünnen Streifen von der Oberfl?che abgeschnitten worden war. Der ‘Formfaktor’ (D), der an Hand der Gleichung 1 errechnet wurde, war bei allen Sorten mit Ausnahme von Cara bei grossen Knollen gr?sser als bei kleinen. Cara hatte auch signifikant niedrigere Werte als die 3 anderen Sorten (Abb. 1B). Diese Variationen bei denD-Werten verursachten sorten- und gr?ssenabh?ngige Fehler in den Voraussagen mittels eines zuvor ver?ffentlichten Formfaktormodells (Abb. 2A). Bei allen Sorten wurde bei Fl?chenmessungen dünner Schalen die wahren Oberfl?chen stets untersch?tzt, wobei sich der Grad der Untersch?tzung mit der Verringerung der Knollengr?sse erh?hte (Abb. 2B). Dieser Effekt wurde auf die offenbare Reduktion des Knollenradius bezogen, die aus der Abplattung der Schalen bis auf eine begrenzte St?rke resultiert. Ein mathematisches Modell, das ein Oberfl?chenintegral (Gleichung 3 oder 4) zur Sch?tzung der Knollenoberfl?che an Hand der Achsenausdehnungen und des Volumens benutzte, ergab ohne signifikante Abh?ngigkeit von der Knollengr?sse bei allen 4 Sorten eine gute Ann?herung an die tats?chliche Oberfl?chengr?sse (Abb. 2C). Das Modell wurde verwendet, um die Sch?leffekte auf die Oberfl?chensch?tzung nachzuahmen, indem die Reduktion der Achsenausdehnungen durch die Schalendicke in die Rechnungen einbezogen wurde (Abb. 3A und 3B).

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Résumé Différentes méthodes utilisées pour évaluer la superficie ont été comparées sur des tubercules des variétés Cara, Désirée, King Edward et Maris Piper. La forme des tubercules dépendait de la variété et de la taille de ceux-ci (fig. 1A). Empiriquement, l'évaluation de la superficie était obtenue en utilisant un ruban adhésif mince autour du tubercule et en mesurant la surface de celui-ci à l'aide d'un planimètre. Dans ce cas, les ‘facteurs de forme’ (D) calculés selon l'Equation 1 s'avéraient plus élevés pour les gros tubercules que pour les petits chez toutes les variétés sauf chez Cara: cette dernière ayant des valeurs significativement plus petites que celles des trois autres variétés (fig. 1B). Ces variations des valeurs deD, données par la variété et la taille des tubercules apportaient une erreur dans la prévision d'un modèle mathématique applicable à la forme (fig. 2A). La mesure par prélèvement d'une mince couche de peau sur toutes les variétés surestimait invariablement la supercifie des tubercules et cette surestimation s'accroissait avec la diminution de leur taille (fig. 2B). Cet effet pouvait être associé à une réduction apparente du rayon du tubercule due aux pelures d'épaisseur constante. Un modèle établi en fonction de la surface intégrale (Equation 3 ou 4) permettait d'évaluer la superficie du tubercule en fonction de ses dimensions axiales et de son volume et donnait une bonne approximation de la superficie réelle pour les quatre variétés, sans dépendance significative de la taille des tubercules (fig. 2C). Ce modèle était utilisé pour simuler les effets du pelage des pommes de terre par rapport à leur superficie en intégrant dans les calculs les dimensions des tubercules avant et après le pelage (fig. 3A et 3B).

     

Some aspects of total losses during storage and reconditioning of potato tubers

Summary Total losses during storage and reconditioning of several Polish varieties and strains in comparison with the American varietyKennebec are discussed. Several varieties or strains show such high losses that they are not acceptable for processing after storage. Susceptibility to loss is an attribute which must be taken into account when assessing varieties.     

Distribution of oxidase enzymes in potato tubers relative to blackspot susceptibility II. Peroxidase and Catalase

Peroxidase and catalase activities in selected potato tuber tissue were studied for differences and possible association with resistance or susceptibility to blackspot. Unbruised stem-end tissue had significantly greater peroxidase activity than did unbruised bud-end tissue. However, there was no significant difference between catalase activity at either end of the tuber; between blackspot susceptibility and peroxidase or catalase activity; and between blackspot susceptible or resistant tissue and the ratio of either catalase or peroxidase to phenolase activity. Bruising did not cause significant changes in either peroxidase or catalase activity or in ratios between these enzymes and phenolase that could be associated with susceptibility or resistance of tissue to blackspot. Studies associating enzymes with potato blackspot susceptibility have been concerned primarily with phenolases (5, 6, 10, 11, 13). Only recently has blackspot susceptibility been considered in connection with activity of other oxidase enzymes (12). It has been known for many years that peroxidase could oxidize many of the same phenols as the phenolases and produce a colored pigment very similar to melanin (7, 8). The study by Weaver et al. (12) was concerned with the possibility of peroxidase contributing to or subtracting from enzymatic discoloration of bruised potato tissue. The study also investigated the inhibitory or accelerating effect of H₂O₂ per se on the rate of oxidation of different phenolic substrates by potato enzymes, and how such reactions could be modified by addition of catalase or peroxidase. The theories of how peroxidase and catalase could contribute to susceptibility to blackspot were also discussed. The purpose of this study was to determine if potato peroxidase or catalase activityper se differed in various parts of the tuber, if these activities could be associated with resistance or susceptibility of the tissue to blackspot, and if certain relationships could be established to predict the response of potato tissue to bruising.     

Inactivation of trypsin inhibitors in sweet potato and taro tubers during processing

In order to understand the extent of elimination of trypsininhibitors during processing of sweet potato (Ipomoea batatas) andtaro (Colocasia esculenta) tubers, a detailed study was conductedusing tubers processed by oven drying, cooking, and microwavebaking. Between 80 and 90% trypsin inhibitor (TI) activity wasretained in sweet potato chips up to 2h at 70 ^°C. Among thefour cultivars of sweet potatoes, RS-III-2 trypsin inhibitors were more heatlabile. Heating at 100 ^°C led to rapid inactivation of TI of sweetpotatoes. Varietal differences in thermal stability were more pronouncedfor the trypsin inhibitors of taro than sweet potatoes. Taro inhibitors werealso more rapidly inactivated than sweet potato TI. Between 17 and31% TI activity was retained in cooked tuber pieces of sweet potatoes,while only 3–10% were retained in taro cultivars. Very effectiveinactivation of trypsin inhibitors of sweet potatoes and taro could beobtained through microwave baking. Flour prepared from taro was devoidof TI activity, while 5–12% TI activity was retained in the flour preparedfrom sweet potatoes. The study clearly established that among the fourtechniques used, microwave baking and flour preparation were the best methods to eliminate TI from sweet potatoes and taro.     

Damage of potato tubers,a review

Summary Damage to potato tubers due to mechanical forces is among the most important causes of loss of quality reported throughout the world. The causes of such damage are mechanical injuries that occur primarily in association with harvesting and grading. The extent of damage is dependent on the condition of the tubers and also reflects the history of the potatoes. Although important advances have been made, there is still a considerable need for research on this subject since knowledge of the combined effects of essential physiological proceses within the cells is still lacking. The avoidance of exposure to mechanical forces constitutes the most effective protection against tuber damage.     

Subcellular localisation of calcium in potato tubers

Summary Deposits, believed to contain calcium, were located in different cells of the potato tuber after using an antimonate procedure. In the starch-storage parenchyma of the medulla and cortex antimonate deposits were abundant within vacuoles, on the tonoplast, and to a lesser extent in cell walls. Phloem tissues contained a high concentration of deposits, mainly within companion cells and phloem parenchyma, consistent sites of deposition being mitochondria, plastids and tonoplasts. Deposits were abundant within vacuoles of cells of the xylem parenchyma. Within vessel elements deposits were limited to the surface of secondary wall thickenings. Antimonate deposits associated with the middle lamella of xylem parenchyma were rarely found. The results are discussed in relation to previous findings for potato tubers and for higher plant cells in general.     

The relationship between respiration and chip color during long-term storage of potato tubers

Processing potatoes, both sprout inhibited and untreated, were evaluated for respiration rate and chip color during storage under commercial conditions (12 C, approximately 95% relative humidity, in darkness) following three growing seasons. While absolute respiration rates varied depending upon growing season and treatment, all cultivars and treatments studied during the 1995, 1996, and 1997 storage seasons showed similar respiration profiles. The initial stage following curing and sprout inhibition treatment (if applied) showed essentially constant respiration rates for a period of time varying from two to 15 weeks, depending upon growing season, treatment and cultivar. This was followed by a stage that showed a linear increase in respiration rates. In some cases the respiration rates eventually stabilized, or decreased. There was an apparent correlation between respiration trends and chip color changes in most cases, though the statistical significance varied between cultivars and seasons. Qualitative analysis of the data showed that the point at which respiration rates began to increase coincided with the onset of the decline in chip color quality. These trends suggest that measurement of tuber respiration may provide a non-destructive andin situ method to predict changes in processing quality of stored potato tubers.     

Inoculation of potato tubers withErwinia carotovora during simulated commercial washing and fluming practices

The potential for bacterial soft rot in potato tubers was affected by laboratory simulation of some components of fluming and washing practices at commercial packinghouses. The potential was expressed as disease severity (average percentage surface decayed) after a standard 4-day incubation at 20°C in a mist chamber. Increased disease resulted when there was an increase in the following factors: a) duration of immersion of tubers in water; b) population of bacteria suspended in water; c) hydrostatic pressure on submerged tubers, and d) concentration of a surfactant (Triton X-100) in the suspensions. A sample of tubers from each tuber lot was uniformly moistened with tap water and then incubated to determine a base-level disease severity. Disease severity in Russet Burbank tubers from commercial storage increased from the base-level of 0.8% to 76% when tubers were immersed in 5 × 10⁶ colony-forming units (cfu)/ml ofErwinia carotovora pv.carotovora (Ecc) for 64 min prior to incubation. Disease severity was 64% when tubers were immersed in a similar suspension for only 0.1 min, but with a hydrostatic pressure of 230 cm of water. Severity values fourto fivefold above control levels (from immersion in water) resulted from an immersion for 5 min in 5 × 10³ cfu/ml with hydrostatic pressures of 5, 180, or 370 cm of water. A 20-fold increase in severity occurred when Red LaSoda tubers were immersed briefly (less than 5 s) in 5 × 10⁶ cfu/ml. Rinsing these tubers with tap water after inoculation, but prior to incubation, did not affect the subsequent development of decay. Thus, the high potential for bacterial soft rot in tubers that have been flumed or washed by water concentrated with soft rotErwinia cannot be reduced by washes or rinses with clean water.     

Development during storage of spraing symptoms in potato tubers infected with tobacco rattle virus

Summary In trials with potato tubers infected with tobacco rattle virus (TRV), symptoms of spraing in cvs Bellona, King Edward, Maris Bard, Matilda, Sv 82146 and Sv 82149 increased during storage when the tubers were cut. Storage of intact tubers at a constant temperature of 9°C or at fluctuating temperatures (2 weeks at 18°C, 2 weeks at 9°C and 2 weeks at 18°C) did not increase the frequency of symptoms.