Suberization and periderm development in Norchief and Red Pontiac potatoes

The largest difference in the rate of wound healing (suberization and periderm development) of cut tubers was attributable to the difference in temperatures (15.5 vs 23.8 C) tubers were stored at after cutting. Lesser differences were found between the Red Pontiac and Norchief cultivars and between the various regions of the tuber. The least difference was found between the different sources of Norchief. Wound healing occurred most rapidly at 23.8 C, in Red Pontiac and in the cortical region of the tuber. It seems probable that a major cause of the high incidence of seed piece decay and poor stands found in Norchief is due to slow wound healing.     

Immunocytological comparison of native and wound periderm maturation in potato tuber

The maturation of potato (Solanum tuberosum L.) tuber native periderm and wound periderm, which develops to replace the native periderm when it is damaged, are agriculturally important processes that are poorly understood. While both types of periderm form from a phellogen layer that serves as a lateral meristem, there has been little research done on comparing the biochemical processes and steps involved in the maturation of the two types of periderm. Here, we use immunological techniques to compare some of the cell wall changes during wound and native periderm maturation. Consistent with our recent work on native periderm, we demonstrate that toluidine blue O is also useful for distinguishing between suberized and non-suberized cells in wound periderm. More importantly, we use the immunological probes JIM5 and JIM7 to show that there is no increase in either un-esterified or esterified homogalacturonan pectin epitopes in phellogen walls accompanying wound periderm maturation. In contrast, as we previously described, native periderm maturation and resistance to excoriation (skinning) is accompanied by an increase in relatively un-esterified and esterified homogalacturonan pectin epitopes in the walls of phellogen cells. These results demonstrate that the biochemical processes responsible for maturation and resistance to excoriation differ between native and wound periderm. This dissimilarity between wound and native periderm maturation demonstrates the potential limitations in applying the wound periderm model to research on native periderm.     

Relevance of immature tuber periderm to high commercial peeling losses

Cell wall composition and histological distinctions between immature and mature periderm are reviewed. The structural characteristics of the periderm of immature tubers vitiate economic peeling. Continuous sloughing and replacement of periderm, occurring with rapid enlargement of Russet Burbank tubers, creates large unsuberized surface areas particularly susceptible to deep penetration of hot caustic and consequent pitting of tubers. The fully developed russetted net of mature periderm is well suberized and holds the caustic so it does not deeply penetrate. Improved crop management and harvest practices could eliminate excessive peel loss due to immature periderm.     

Relationship of potato tuber periderm resistance to plant water status

Potato (Solanum tuberosum L. cv. Russet Burbank) tuber periderm resistance to water loss was monitored during the harvest season. Periderm resistance of tubers from water-stressed plants was compared with tubers from unstressed plants throughout a six-week harvest period, in order to determine the effect of plant condition on tuber resistance to water loss. Tubers stored for ten days at 4°C immediately following harvest were also monitored to determine if storage enhanced periderm resistance and if any difference occurred between tubers from stressed vines compared with those from unstressed vines. During the harvest season, tuber resistance to water loss was positively correlated with plant water stress, as measured by leaf water potential and leaf diffusive resistance. Storage of tubers after harvest also caused an increase in periderm resistance. The commercial practice of vine killing, therefore, may have a positive effect on reducing weight loss in storage by enhancing the resistance of tuber periderm to water loss.     

Comparison of periderm color and anthocyanins of four red potato varieties

The color, anthocyanin content per given surface area, and phenolics content of tuber periderm of four different varieties of red potatoes were compared. Three of the varieties, Norland, Red Norland, and Dark Red Norland, are members of a color sport family. Freshly harvested ‘Norland’ differed significantly in color, but not anthocyanin content per given surface area, from its sports. ‘Red Norland’ tubers were lighter in color than those of ‘Dark Red Norland’. In general, storage resulted in darkening of tubers and, except for the fourth variety, MN17922, a decrease in anthocyanin content per given surface area. Tubers from green-killed ‘Red Norland’ plants were more purplish-red than those from vine-killed plants. Stored tubers had greater periderm total phenolics content than freshly harvested tubers. The increase in periderm phenolics and decrease in anthocyanin content per given surface area may lead to darkening of tubers with storage. Cell walls connecting periderm to cortex tissue of ‘MN17922’ tubers were thinner than those in ‘Norland’ tubers, which may explain why it is realtively easy to separate the periderm of ‘MN17922’ from its cortex.     

Helminthosporium solani Dur. & Mont. development on potato periderm

Development ofHelminthosporium solani Dur. & Mont. on artificially inoculated, excised potato tuber periderm, incubated in darkness and high humidity at 20 to 24°C, was studied using light and scanning electron microscopy. Spore germination occurred within 16 hours, and appressoria were observed 2 days after inoculation. Penetration of periderm was evident 4 days after inoculation. Conidiophores with young conidia developed on the periderm surface within 7 days of inoculation. Well-developed conidia were visible often by 9 days after inoculation. Rudimentary stromata were observed beneath conidiophore groupings at later stages of development. In histological studies,H. solani hyphae were found in the phellem, phelloderm, and cortex of infected tuber sections. Basal cells of conidiophores or stromata were observed on the surface and in the outer tangential cork cell layers. Several layers of suberized and sometimes collapsed cortical cells were observed beneath disrupted and collapsed, infected periderm. Cavities sometimes formed between periderm and cortex, and callosities were observed on cell walls of some cortical cells beneath infected periderm.     

Techniques for detecting and measuring developmental and maturational changes in tuber native periderm

We developed a technique to quantitate native periderm permeability during tuber growth and maturation by porometrically determining vapor conductances. We also describe a simple, inexpensive means of determining the corresponding weight per unit area of suberized phellem cells (skin) in native periderm during tuber growth and maturation as a means of assessing the developmental status of native periderm. The porometric technique is very sensitive and rapid. Porometrically derived vapor conductances of mature native periderms were measured without difficulty, and native periderms were found to release ~0.005 moles of water vapor/meter² native periderm surface/sec. into a dry test atmosphere. Immature native periderm released up to 28 times more water vapor than mature periderm even though the phellem cells were histochemically determined to possess both major components of suberin. We demonstrated use of the porometric technique by determining maturational changes in periderm permeability of growing/immature tubers and mature tubers at harvest. The technique revealed that the native periderm of Russet Burbank tubers was more permeable and had the potential to lose more water vapor, until becoming permeably mature, than Norchip or Norland tubers harvested on the same dates. The dry weight of the skin (phellem tissue) of native periderm (mg/ cm²) for all three cultivars increased during tuber growth, but plateaued to a relatively constant level, or slightly declined, while plants were still alive during the latter period of tuber growth. During this period, periderm vameable conductances were undergoing substantial declines. Comparison of skin dry weights of immature tubers indicated that stem end regions of tubers were developmentally ahead of equatorial and bud end regions; this difference decreased as the tubers matured at harvest time and was less apparent with some cultivars.     

The effect of some vine desiccants on periderm development on cut potato tuber pieces

Russet Burbank, Red Pontiac, and Superior potato plants were treated with vine desiccants at the rate of 0.50 kg/ha and 1.12 kg/ha paraquat + X77, diquat + X77 and 2.24 kg/ha of Dow General, alone and with Crop Oil, 2 to 4 weeks before harvest. Untreated and treated tubers were selected for anatomical examination directly after harvest and after 22 weeks of storage. The tubers were cut in half longitudinally and exposed to optimum environmental conditions for 25 days when they were examined for periderm formation. Wound periderm in untreated tubers consisted of uniformly shaped and continuous layers of cambial cells. Tubers treated with 0.56 kg/ ha paraquat had a less developed periderm than untreated ones, but it would serve as a barrier against the invasion of pathogens. Diquat at the same concentration had fewer cambial cells and they were not continuous so that pathogen entrance was possible. With 1.12 kg/ha paraquat the periderm was less and with diquat more differentiated than the 0.56 kg/ha treatment indicating that concentration had some effect. Treatment with Dow General resulted in the formation of a periderm adequate for prevention of pathogen entrance. The effectiveness of the 3 chemicals to form periderm in Superior and Red Pontiac was similar to that of Russet Burbank. Periderm was most highly differentiated in untreated tubers followed by paraquat, Dow General, and diquat treated tubers.     

Pink eye is an unusual periderm disorder characterized by aberrant suberization: A cytological analysis

Potato tuber pink eye (PE) is a disorder of unknown origin that results in significant postharvest quality deterioration and rot. Little is known about the physiology of PE, including the characteristic tissue autofluorescence that defines the PE syndrome. The objective of this research was to identify the source of PE-induced autofluorescence and PE-related susceptibility to infection. The suberized barrier of the native periderm and cellular characteristics of neighboring parenchyma tissues were investigated to determine their involvement in the PE disorder. The results create a new physiological model describing the disorder and addressing the enigma of PE. Characteristics of the PE model emerge from the following results: (1) the integrity of the suberized barrier of the native periderm was compromised or absent in some surface areas of PE tubers thereby implicating the breakdown of the native periderm and its associated suberin barrier with PE and the susceptibility of PE tubers to pathogen infection; (2) the PE complex was characterized by unusual suberin poly(phenolic) (SPP) accumulations in the cortical parenchyma followed by latent suberin poly(aliphatic) (SPA) accumulations that were generally insufficient to form a complete barrier that was competent to block infections by pathogenic bacteria and fungi; (3) the aberrant absence or compromised integrity of the suberin barrier, including associated waxes, resulted in erratic increased susceptibility to water vapor loss known to cause tuber shrinkage and flaccidity; (4) widespread accumulations of SPP on parenchyma cell walls were the durable source of autofluorescence commonly used to determine the presence of the disorder; (5) the erratic development of unusual internal phellogen and periderm layers that, if complete with SPA, blocked hyphal advancement; (6) combined, the data provide a plausible explanation for PE infection court and rot anomalies as they occur without ingress of a wound opening. Results also demonstrated that neutral red may be used as a sensitive fluorochrome to detect intact hydrophobic areas in hyphae. Collectively, the results provide compelling evidence that the PE disorder includes a physiological basis.     

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.

     

Vaughn and Lulai: Suberin stains comparison of fluorescent stains for the detection of suberin in potato periderm

Several fluorescent staining procedures to detect suberin in normal periderm of potato were assessed. Among the stains tested, treatment with the alkaloid fluorochrome berberine followed by counterstaining with crystal violet appears to be the most sensitive combination. Crystal violet increased contrast by quenching lignin fluorescence which is also present in the periderm cell walls. This technique may be useful for studying the role of suberin in disease resistance and wound healing of potato tubers and other tissues.     

The influence of tuber position on periderm calcium content and its relationship to soft rot susceptibility

Summary Calcium levels in the periderm of tubers (cv. Sebago) growing in irrigated sands were influenced by the stem position at which the tuber grew, but the effect was not consistent over two seasons. Calcium levels were increased at all tuber positions by addition of calcium to soil; combined treatments of gypsum (1400 kg Ca²⁺/ha) pre-plant and calcium nitrate (37 kg Ca²⁺/ha) side dressings gave the greatest response. Percentage incidence of soft rot lesions caused byErwinia chrysanthemi pv.zeae was not influenced by periderm calcium content. The severity of infection (weight of tissue macerated within 48 h at 30°C) was significantly reduced only by the pre-plant gypsum treatment, but there was no correlation with calcium content of the periderm. Calcium levels in periderm tissue (60–208 mg Ca²⁺/100g) are within the range of published data for other cultivars and results support previous reports that the correlation between tuber susceptibility toErwinia spp. and periderm calcium content is inconsistent.     

Accumulation of mineral elements in tuber periderm of potato cultivars differing in susceptibility to common scab

Summary Concentrations of Ca, P, K, Mg, Al, Fe, Mn, Cu and Zn were determined in healthy tuber peelings of cultivars less (Karin, Santé and Symfonia) and more (Agria, Désirée and Tomensa) susceptible to common scab when grown at two sites that differed in the level of scab incidence. The accumulation of some elements was significantly influenced by site, year, cultivar, maturity and the age of tuber periderm. At both sites, Ca and P in periderm tissue declined but Mg increased during the growing season. The Ca/P ratios in tuber periderm of all cultivars greatly decreased 83 days after planting. Concentrations of mineral elements measured at harvest may not reflect conditions present during the infection period, and consequently may not be related to scab incidence or severity.     

Scanning electron microscope observations of the development of sporophores ofColletotrichum atramentarium (B. et Br.) Taub. on infected potato periderm

Sections of potato periderm (1cm²), bearing sclerotia ofC. atramentarium were incubated for 16 days at 25°C, fixed in OsO₄ vapor at room temperature, dehydrated in a graded ethanol series and stored in 100% ethanol. Fixed specimens were coated with gold and examined with a Stereoscan electron microscope. Initial observations revealed numerous sclerotia and non-spore producing acervuli. After 16 days acervuli in various stages of development were observed. Initial development consisted of periderm swellings caused by a sclerotial body which enlarged to occupy an entire cork cell and eventually ruptured the periderm. A palisade layer formed from which setae developed, and apical ends of conidiophores were evident. Further development of the palisade layer was partially obscured by extrusion of a mucilaginous layer. Cylindrical, single-celled conidia (2.2–3.8u x 14.4–19u) were extruded through the mucilaginous matrix. Remnants of periderm wall were associated with acervuli and conidia lay in closely packed masses around the bases of mature acervuli. Conidia washed from spore producing acervuli onto PDA, germinated within 24 hours at room temperature. Electron scan is a rapid method for following acervulus development ofC. atramentarium on diseased potato periderm and demonstrates the feasibility of studying other potato periderm diseases with this technique.     

The formation of wound periderm and the susceptibility of potato tubers to gangrene (caused byPhoma exigua) in relation to rate of fertiliser application and time of planting

Summary Wound periderm on potato slices restricts the penetration of the underlying tissue byPhoma exigua f. sp.foveata. The rate of formation of the wound periderm on slices cut from freshly harvested tubers may be affected by the rate of application of NPK fertiliser and by the time of planting of the crop. These two factors also influence the susceptibility of the tubers to gangrene induced by artificial inoculation, but the correlation between rate of formation of wound periderm and incidence of rot was not consistent.

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Zusammenfassung Das Wachstum vonPhoma exigua f. sp.foveata im Knollengewebe wurde durch Aufschub der Inokulation der Schnittoberfl?che gehemmt. Gleichzeitige Prüfung der Bildung von Wundperiderm unter gleichen Bedingungen ergab, dass diese Hemmung eintrat, bevor die erste Schicht des Wundperiderms sichtbar verkorkt war bei 15°C und 95% RF (Tabelle 1 und 2). Wundperiderm dürfte schneller gebildet werden bei Scheiben von Knollen aus Parzellen mit kleinen Düngergaben, aber die Enddicke der verkorkten Schicht wurde nicht beeinflusst durch die Gr?sse der gegebenen Düngermenge (Tabelle 3 und 4). Knollen, die in Parzellen mit kleinen Düngermengen erzeugt und zur Zeit der Ernte mitP. exigua f. sp.foveata inokuliert worden sind, reagierten empfindlicher auf die Ausbreitung der F?ule im Knolleninnern als jene, die mit einer gr?sseren Düngergabe wuchsen (Tabelle 5). Die Bildung von Wundperiderm, untersucht bei der Ernte 1965 und 1966 an Erzeugnissen aus Parzellen, die in Abst?nden von 2 Wochen angepflanzt wurden, war kleiner in den Knollen aus im April und Anfang Mai angepflanzten Parzellen. Der Befall mit Phomaf?ule durch natürliche Infektion war im ersten Winter h?her bei den Mustern, bei denen die anf?ngliche Verkorkung langsamer vor sich ging, nicht aber im zweiten Winter (Tabelle 6). Künstliche Inokulation von Knollen aus den Parzellen im zweiten Jahr zeigte, dass eine Verz?gerung im Auspflanzen die Art der sich entwickelnden L?sion beeinflusst. Kleine, tiefe L?sionen traten bei Knollen aus Parzellen mit früher und weiter Pflanzung auf, oberfl?chliche L?sionen entwickelten sich bei Knollen aus sp?teren Pflanzungen (Tabelle 7).

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Résumé Une inhibition du développement dePhoma exigua (f. sp.foveata) dans le tissu de pomme de terre apparait avec le retardement de l’inoculation des surfaces sectionnées. L’examen simultané de la formation du périderme de blessure sous des conditions semblables indique que cette inhibition appara?t avant que la première couche du périderme de blessure soit visiblement subérisée à 15 C et 95% RH (Tableau 1 et 2). Le périderme de blessure peut se former plus rapidement dans des tranches sectionnées provenant de tubercules formés avec de faibles quantités de fertilisants, mais l’épaisseur finale de la couche subérisée n’est pas affectéc par la quantité de fertilisant appliqué (Tableau 3 et 4). Les tubercules formés avec de faibles doses de fertilisant et inoculés avecP. exigua (f. sp.foveata) au moment de la récolte sont plus susceptibles à l’extension de la pourriture que ceux développés avec des doses plus élevécs de fertilisant (Tableau 5). La vitesse de formation du périderme de blessure, testée à la récolte en 1965 et 1966 sur la production de parcelles plantées à des intervalles de 2 semaines, était moindre dans les tubercules provenant de parcelles plantées en avril et début de mai. On a remarqué une incidence plus élevée de gangrène provenant d’infection naturelle le premier hiver dans les échantillons dans lesquels la tubérisation initiale est moins rapide, mais non le second hiver (Tableau 6). L’inoculation artificielle des tubercules provenant des parcelles de seconde année indique que le retard dans la plantation effecte le type des lésions qui se développent. Des lésions limitées et profondes apparaissent dans les tubercules de parcelles plantées t?t et des lésions larges, superficielles se forment dans les tubercules de plantations tardives (Tableau 7).

     

ESTIMATING THE SOIL CONTENT OF HERBAGE COLLECTED BY FORAGE HARVESTER

A method is described Tor estimating the amount of contamination by soil caused when herbage is collected with a forage harvester. Hand-cut samples of herbage are used as a control. To avoid sub-sampling errors a relatively large sample is used. It is oven-dried and then compressed to facilitate ashing. Acid-insoluble ash ("silica") content is used as a measure of contamination. The Statistical examination of the data is discussed briefly.     

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