Blackspot of Russet Burbank potatoes and the carbon dioxide content of soil and tubers

These studies were designed to elucidate the influence of CO₂ on blackspot susceptibility of Russet Burbank potatoes. The influence of tuber CO₂ environment on blackspot was tested. Tubers from 1–4 and 6–8 inches deep in the soil were scored for blackspot and moisture samples were taken from their vicinity. Blackspot was worse in shallow tubers and in tubers from drier soil. Plowing under corn stover, covering the soil with plastic, and excessive irrigation failed to cause blackspot susceptible tubers. Diffusing CO₂ into the soil atmosphere under plastic sheets slightly increased the intensity of spot discoloration but the discoloration was atypical blackspot. Effects on blackspot by changing tuber gases was tested. Tubers whose gases had been evacuated and replaced by O₂, N₂, and CO₂ had lower blackspot scores than untreated tubers. Increasing the time tubers were soaked in water after gaseous evacuation reduced blackspot. Hydration consistently decreased tuber blackspot. In chemical studies, tubers were tested for blackspot and analyzed for CO₂ content. The relationship between tissue CO₂ and blackspot appeared to be inverse. Tuber CO₂ content was not influenced by time of day. Tuber blackspot scores immediately, 1, 3, and 7 hours after digging were the same, but tissue CO₂ content increased linearly with time after harvest.     

The effect of controlled atmosphere storage at 4°C on crisp colour and on sprout growth,rotting and weight loss of potato tubers

Summary After three weeks curing at 10°C, potato tubers cv. Record were stored at 4°C under different controlled atmospheres (CA) for six months to study the effect on crisp fry colour, sprout growth and rotting. Combinations of low levels of CO₂ (0.7–1.8%) and low levels of O₂ (2.1–3.9%) gave a significantly lighter crisp colour, low sprout growth and fewer rotted tubers compared with 0.9% CO₂ and 21.0% O₂. Tubers stored in these conditions. showed a significantly higher weight loss and shrinkage after reconditioning. High CO₂: low O₂ combinations during storage completely inhibited sprout growth and caused the darkest crisp colour, but after reconditioning tubers gave the same level of sprouting and crisps as light as the other CA combinations. Furthermore these combinations, especially CO₂ at 10 or 15%, increased the onset of rotting. Also our results showed that at low concentrations of CO₂ (0.7–1.6%), and low O₂ (2–2.4%) there was an increase in tuber rotting.     

Enhanced dormancy release and emergence from potato tubers after exposure to a controlled atmosphere

The North American potato industry requires an effective and environmentally-appropriate, dormancy-release methodology. The present study examined dormancy release and subsequent sprout emergence based on a modified, controlled-atmosphere (CA) approach using such environmentallycompatible gases as nitrogen, carbon dioxide and oxygen with or without trace amounts of ethylene (50 ppm). This paper is the first published report of a semi-automated, controlled-atmosphere system for dormancy release of potato tubers. The system allows computer-controlled gas application and analysis for up to four gas mixtures simultaneously. Low oxygen concentrations (< 10%) for 10 days in the presence of 10 to 60% carbon dioxide or a high carbon dioxide (60%)/oxygen (40%) treatment caused tuber breakdown regardless of cultivar. The most effective mixtures for enhanced dormancy release and sprout emergence were 20% CO₂/40% O₂ or 60% CO₂/18-20% O₂ and their effects were further enhanced by 50 ppm C₂H₄ (ethylene). In the presence of 50 ppm C₂H₄ the 20% CO2/40% O₂ mixture was comparable to bromoethane in effectiveness. Temperature and light exposure affected subsequent Russet Burbank tuber responses to CO₂/O₂/C₂H₄ gas mixtures.     

Rates of internal blackspot bruise development in potato tubers under conditions of elevated temperatures and gas pressures

Internal blackspot bruising was produced in Russet Burbank tubers by dropping a 150 g weight 40 cm through a slotted guide tube and incubating the tubers for varying time periods at temperatures ranging from 10 to 80 C. When potatoes were bruised following 1 to 5 months storage, those tubers incubated at 10 C required 48 hr for maximum blackspot development. Increasing the incubation temperature accelerated blackspot formation with an optimum response at 36 to 40 C. At 40 C tubers reached maximum discoloration within 6 hr. Bruised tubers were also exposed to combinations of varied temperatures and varied gas pressures of 0.3 to 2.1 kg/cm² using air, O₂, CO₂, and N₂. Pressurized air slightly enhanced the temperature effect at 40 C; pressurized O₂ had no significant effect upon blackspot development, while CO₂ and N₂ inhibited blackspot formation. Blackspot bruises incurred in the field during harvest required a longer incubation period at a lower temperature than did bruises inflicted on tubers held in storage for 1 to 5 months.     

The pattern of assimilate movement in potato plants

Summary Leaves at nodes 5, 7 and 9 (numbered from the base) on separate batches of plants were supplied with¹⁴CO₂ at flowering and to further batches of plants 20 and 40 days after flowering. Of the tubers formed on a plant 20% arose from that portion of the stem within an arc of ±45 from the supply leaf but they contained 47% of the activity detected in all of the tubers.     

The influence of storage factors on endogenous ethylene production by potato tubers

Throughout a 7-month storage period, Russet Burbank tubers continuously ventilated at 32 F (0 C) and 45 F (7.2 C) with atmospheres of 2% O₂, air, 4% CO₂, and intermittently ventilated with air, evolved ethylene at a rate no greater than 0.008 μ 1 Kg^?1 hr^?1. Tubers stored in 80% O₂ and 12% CO₂ produced ethylene at much higher rates. In all cases where sprouting occurred, the rate of ethylene production increased. Inoculation withFusarium roseum greatly stimulated ethylene production but inoculation withAlternaria solani did not.     

Enzyme-linked immunosorbent assay (ELISA) for the detection of potato leafroll virus and potato virus Y in potato tubers after artificial break of dormancy

Summary Conditions necessary for the detection of potato leafroll virus (PLRV) and potato virus Y (PVY) in tubers from primary and secondary infected plants were investigated. Tubers were analysed before and after breaking dormancy by rindite treatment. PLRV was reliably detected indormant tubers whereas PVY was readily detected only when tubers had been rindite-treated and held for two to three weeks at 22°C and high humidity in the dark. PLRV occurred in higher concentration at the heel end than at the rose end of infected tubers and the concentration remained nearly unchanged during the experimental period of 35 days, whereas PVY was found to be more concentrated at the rose end and was rapidly accumulating in the tubers after the break of dormancy. In dormant tubers PVY concentration dropped during storage at 22°C. The use of ELISA for tuber indexing is discussed.     

Temperature,cyanide, and oxygen effects on the respiration,chip color,sugars, and organic acids of stored tubers

The possibility that sugar accumulation of potatoes stored at low temperatures may be linked to activation of cyanide-resistant respiration (CRR) was investigated. After a lag period of several days, continuous HCN treatment stimulated CO₂ production of tubers stored in 20% O₂. At 1°C in 20% O₂, HCN treatment increased respiration over that effected by low temperature treatment. After several weeks of treatment, cyanide-stimulated CO₂ production was greater at 1°C than at 10°C. Sucrose and malate levels of HCN treated tubers were sometimes higher than those of the 10°C control tubers, but they were always lower than those of the 1°C control tubers. This indicated that CRR alone could not account for the sugar increases at 1°C. Storage in 2% O₂ blocked the increase in CO₂ production and changes in constituents associated with HCN treatments in 20% O₂. HCN treatment had no significant effect on chip color. The level of CRR was measured in freshly cut slices from Monona, Norchip, and Kennebec tubers previously stored at 10°, 5°, or 1°C for several months. Slices from tubers previously stored at 1°C had increased CRR, but there was no difference in CRR between the 5°C and 10°C treatments. Sugars accumulated at 5°C, again indicating that sugar accumulation in potatoes stored at low temperatures was at least partially independent of the activation of CRR.     

The release of methyl chloride from potato tubers

Freshly harvested Norchip and Kennebec tubers release varied amounts of methyl chloride (CH₃Cl) during suberization. Maximum rates of CH₃Cl release, ranging from 98-690 ng CH₃Cl/kg tubers/hr under laboratory and commercial conditions, were attained 2–3 days following harvest. Release rates thereafter decreased 10-40-fold by the 7th day of suberization. The period of rapid decrease in CH₃Cl release corresponds to the reported time required by cut tuber tissue to initiate resistance to water loss. Cutting of newly harvested and suberized Kennebec tubers reestablished the high release rates of CH₃Cl measured during the early stages of suberization. The enhancement of CH₃Cl release by tissue cutting was not demonstrated by two varieties stored for 10 months. Suberization differences between early and late harvested Norchip tubers were better differentiated by their respective rates of CH₃Cl release than by CO₂ generation. These preliminary findings suggest the rate of CH₃Cl release could be applied to assess harvest damage and monitor the suberization process. Methyl chloride has previously been reported as the major nonindustrial chlorocarbon in the atmosphere that is linked to a replenishable, natural source.     

Influence of heat stress on dry matter production and photo-assimilate partitioning by four potato clones

Partitioning patterns of¹⁴C labeled assimilates were studied to determine their relationship to dry matter accumulation and distribution in four potato clones (Desiree, DTO-28, LT-1 and Russet Burbank). Plants placed in growth chambers at 35/25 C day/night temperature and 12-hour photo-period two weeks after tuber initiation were compared with plants grown continuously at 25/12 C. Two weeks after temperature treatments were begun, the most recently expanded leaf was labeled with¹⁴CO₂ for 30 minutes, and plants were harvested 20 hours or 15 days later. High temperature reduced total dry matter production and altered dry matter distribution in favor of vines at the expense of tubers. Partitioning of¹⁴C assimilates generally followed the pattern of dry matter distribution. Potato clones exhibited variation in¹⁴C assimilate export from labeled leaves and in partitioning to vines and tubers. Assimilate partitioning to tubers was not consistently higher in clones considered heat tolerant.     

Métabolisme des lipides dans le tubercule de pomme de terre (Solanum tuberosum L.). 1. Evolution des lipides au cours de la conservation des tubercules

Résumé Le métabolisme des lipides des tubercules de pomme de terre au cours de leur conservation à différentes températures ou sous des atmosphères de composition variée, a été étudié, et les modifications induites pour un traitement à la ‘rindite’ mélange synergique connu pour lever le repos végétatif, ont été examinées. Une augmentation appréciable de la teneur en acides gras totaux dans la pulpe a été enregistrée à 0,4,10 et 18°C, dans les premiers mois de conservation. Une chute de la teneur en acides gras totaux de la pulpe a été notée au cours de l'entreposage dans les atmosphères enrichies en CO₂ (20%) ou en O₂ (37%). La ‘rindite’ provoque une synthèse accrue de lipides, surtout dans la période de croissance active des germes.

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Summary The potato tuber is low in lipids, which form only 0.1% of the fresh weight of the tissue. Of the tuber lipids, 60–80% are unsaturated fatty acids, linoleic acid predominating (Tables 1 and 2). It has been observed that there is an appreciable increase in the total fatty acid content of the tuber flesh during storage at 10°C and 18°C. This increase occurs mainly during the phase of rapid sprout growth, thus fairly long after the tubers have broken dormancy. The increase continues in the case of tubers stored at 10°C, up to the stage of incubation or tuberisation of the sprouts. The opposite occurs in tubers stored at 18°C; total fatty acids decrease during this period. This is probably due to a physiological imbalance of the cells arising from a heavy loss of water by the tubers (Fig. 3). With regard to tubers stored at low temperature (0°C and 4°C), it has been noted that the total fatty acid content increases (accompanied by an increase in the degree of unsaturation of the lipids). This increase is followed by a marked fall during the final months of storage. This could be accounted for either by a disturbance of cellular function at low temperature or by a progressive degradation of the lipids by lipases (Fig. 3). Study of tuber storage in different atmospheres gave interesting results. The mixture enriched with oxygen (37%) partially inhibits sprout extension and apical dominance; air containing 20% CO₂ totally inhibits sprouting and leads to the death of the tuber. On the other hand, air containing 6% CO₂ accelerates sprouting, leads to earlier tuberisation of the stolons and increases the number of tubers formed per sprout. Such a result could be of interest in practical agronomy (Fig. 4). It was observed that, with the onset of sprouting, there is an increase in total fatty acids in the flesh of tubers stored in air enriched with CO₂ (6%). This is followed by a decrease. In the case of air containing 20% CO₂, even if the total fatty acid content remains more or less static for a period, a sharp fall follows. On the other hand, the flesh of tubers stored in air and in an atmosphere low in oxygen shows an appreciable increase in total fatty acid content; whereas in air enriched with oxygen (O₂:37%) there is a fall (Fig. 5). ‘Rindite’, a compound which breaks dormancy, has a marked effect on the formation of fatty acids in the tuber parenchyma. It leads to a progressive synthesis of lipids. particularly during the period of active sprout growth. This increase in the total fatty acid content affects particularly the unsaturated fatty acids and also palmitic acid. This increase in lipid synthesis could be due to a general increase in carbon metabolism by the ‘rindite’ (Fig. 7 and 8).

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Zusammenfassung Die Kartoffelknolle ist ein an Lipiden armes pflanzliches Organ, stellen diese Verbindungen doch nur ungef?hr 0,1% der Frischsubstanz dar. Die wesentlichen Lipide der Knolle sind reich an unges?ttigten Fetts?uren (60–80%), wobei die Linols?ure vorherrscht (Tabellen 1 und 2). Man hat festgestellt, dass im Verlauf der Lagerung bei 10°C und 18°C eine nennenswerte Erh?hung im Gesamtgehalt an Fetts?uren im Knollenfleisch erzeugt wird. Diese Erh?hung findet vor allem w?hrend der raschen Wachstumsphase der Keime statt, also ziemlich lange Zeit nach Ende der Keimruhe der Knollen. Diese Erh?hung setzt sich fort bei den bei 10°C gehaltenen Knollen bis zum Stadium der Inkubation oder der beginnenden Knollenbildung. Dagegen ist bei den bei 18°C aufbewahrten Knollen eine Verminderung der Gesamtmenge der Fetts?uren w?hrend dieser Periode festzustellen; diese Tatsache ist wahrscheinlich auf ein physiologisches Ungleichgewicht der Zellen zurückzuführen, das von einem starken Wasserverlust der Knollen herrührt (Abb. 3). Was die Knollen betrifft, die bei niedriger Temperatur aufbewahrt wurden (0°C und 4°C). so hat man ein Ansteigen des Gesamtgehaltes an Fetts?uren bemerkt (begleitet von einer Abnahme des Grades der S?ttigung der Lipide). Dieser Steigerung folgt ein starker Abfall w?hrend des letzten Monates der Lagerung. Für diese Tatsache kann eine Erkl?rung gefunden werden, sei es in der Unregelm?ssigkeit des Funktionierens der Zellen bei tiefen Temperaturen, sei es in einer wachsenden Degradation der Lipide durch die Lipasen (Abb. 3). Das Studium der Lagerung von Kartoffelknollen unter verschiedenen Atmosph?ren hat interessante Ergebnisse gebracht. Das mit Sauerstoff angereicherte Gemisch (37%) hemmte teilweise das L?ngenwachstum der Keime und die apikale Dominanz; die mit 20% CO₂ belastete Luft verhindert die Keimung vollst?ndig und führt zum Tod der Knolle. Dagegen beschleunigt die mit 6% CO₂ belastete Luft die Keimung, f?rdert die frühere Knollenbildung der Stolonen und erzeugt pro Trieb eine gr?ssere Anzahl von Tochterknollen. Ein solches Ergebnis k?nnte für die landwirtschaftlich Praxis von Interesse sein. Man hat zu Beginn der Keimung ein Ansteigen des Gesamtgehaltes an Fetts?uren im Fleisch von Knollen, die in mit 6% CO₂ angereicherter Luft gelagert wurden, festgestellt. Auf diesen Zuwachs folgt eine Abnahme. Wenn die Luft mit 20% CO₂ angereichert war, ging der Gesamtgehalt an Fetts?uren, wenn er w?hrend einer gewissen Zeit auch beinahe gleich blieb, nachher doch deutlich zurück. Dagegen stieg in nennenswerter Weise der Gesamtgehalt an Fetts?uren im Fleisch von Knollen, die bei normaler Luftzusammensetzung und in sauerstoffarmer Atmosph?re gelagert wurden; in mit Sauerstoff angereicherter Luft (O₂:37%) f?llt der Gehalt an diesen S?uren stark (Abb. 5). Die Wirkung der ‘Rindite’, einem Mittel zur Brechung der Keimruhe, auf die Weiterentwick lung der Fetts?uren des Parenchyms der Kartoffelknolle ist sehr deutlich. Sie bewirkt eine wachsende Synthese von Lipiden, besonders in der aktiven Wachstumsperiode der Keime. Dieses Ansteigen des Gesamtgehaltes an Fetts?uren betrifft besonders die unges?ttigten Fetts?uren und auch die Palmitins?ure. Diese Zunahme der Lipid-Synthese k?nnte auf eine allgemeine, durch ‘Rindite’ hervorgerufene Beschleunigung des Kohlenstoff-Stoffwechsels zurückgeführt werden (Abb. 7 und 8).

     

The influence of storage conditions on physical and physiological characteristics of Shepody potatoesa

Summary The influence of storage temperature (pre-storage, 3 °C, 7 °C, and 9 °C) and controlled atmospheric (CA) conditions (7 °C, 2% O₂, 10% CO₂) were evaluated relative to the physiology and mechanical failure properties of potato tubers (Solarium tuberosum L. cv. Shepody). Mechanical properties of the tuber tissue differed by storage treatment although the physical properties could be generally explained by the measured relative turgor of the tissue. Models typically ascribe lower tissue toughness to greater tissue turgor. In this study, prior to storage tubers exhibited characteristics of greater tissue toughness (20.3 MPa) in conjunction with high relative tissue turgor (as measured by shock wave speed, 115 m/s). It appears that tubers prior to storage have quantitatively stronger tissue compared to tubers after storage regardless of hydration level. CA storage altered tissue mechanical properties as well as carbohydrate content and had physiochemical characteristics of tubers stored at 3 °C;. Idaho Agricultural Experiments Stations paper no.00710, Moscow, ID, USA.     

Naturally-occurring aromatic compounds inhibit potato tuber sprouting

Several naturally-occurring aromatic aldehydes and an aromatic alcohol inhibited potato tuber sprouting when applied as volatiles or directly as emulsions. Exposure to volatiles was for 1 or 10 days prior to placement into fresh air. Salicylaldehyde inhibited sprouting of tubers exposed for 1 or more days; benzaldehyde, cinnamaldehyde, cuminaldehyde and thymol suppressed sprouting of tubers exposed for 10 days. Direct application of cinnamaldehyde and benzaldehyde as 1% and 10% emulsions completely inhibited sprouting 14 days after treatment without apparent tuber damage. These compounds applied without dilution inhibited sprouting but damaged tubers.     

Factors influencing the soft-rotting of potato tubers by bacteria

Summary The production of extensive soft rot in potato tubers which were wounded, inoculated withErwinia carotovora var.atroseptica and stored inc. 100% RH at 20° was greatly increased by replacing air in containers with N₂. Accumulation of CO₂ due to tuber respiration did not significantly affect the production of rots in these conditions. When tubers were inoculated with sterile water in place of theErwinia and held under anaerobic conditions, spreading soft rots were also produced andClostridia, but not soft rotErwinia, were isolated from the rotted tissue. Some of theseClostridia were shown to be capable of breaking down potato tissue, and may be a significant cause of potato soft rots developing in store.     

The effect of oxygen concentration upon sprout growth on the potato tuber

Summary The external oxygen concentration in which the greatest number of buds started to grow at 10–20 C rose during the storage season, from 2–4% in January to 14–23% in June. There was a similar rise in the concentration which was optimal for the rate of sustained sprout growth, from 4–5% to 17–20%. 5% O₂, which stimulated growth early in the storage season, caused marked suppression late in the season, this effect showing earlier in tubers previously stored at 2 or 4 C than in those stored at 10 C. It is suggested that two effects of oxygen may be discernible, involving an optimally anaerobic reversible metabolism of a growth inhibitor and an aerobic requirement for growth. The possibilities are discussed that the enzyme system concerned in the former may be sulphydryl dependant, and that the direction of reaction may show parallelism with sucrose accumulation in the tuber.

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Zusammenfassung Der Beginn des Keimwachstums und das Ausmass der anschliessenden Entwicklung wurden in O₂-Konzentrationen von 1–50% bestimmt, wobei der Rest der Atmosph?re aus N₂ (kein CO₂) bestand. Die interzellularen O₂-Konzentrationen wurden entsprechend den verschiedenen Aussenkonzentrationen errechnet. Das Keimgewicht in Prozenten, die Anzahl der messbaren Keime (> 1 mm) und die durchschnittliche L?nge und Dicke des l?ngsten Keimes pro Knolle wurden notiert (Tabellen 1, 2 und 3), ebenso wurden die H?ufigkeitsverteilungen der verschiedenen Keiml?ngen in den Keimpopulationen (Tabellen 4, 5 und 6) zusammengestellt. In einer Versuchsserie wurde das weitere Wachstum des l?ngsten Keimes jeder Knolle in vier aufeinanderfolgenden Versuchen w?hrend der Lagerung gemessen (Abb. 1). Bei Knollen, die sich am Anfang eines Versuches offenbar noch in der Keimruhe befanden, begann das Wachstum in 5% O₂ früher als in Luft Die ?ussere Sauerstoffkonzentration, in der die gr?sste Anzahl der Knospen bei 10–20 C zu wachsen begann, stieg w?hrend der Lagerungszeit von 2–4% im Januar auf 14–23% im Juni (Tabellen 2 und 3) an. Ahnlich stieg die Konzentration, die für die Schnelligkeit des ununterbrochenen Keimwachstums optimal war, von 4–5% auf 17–20% (Tabellen 2 und 3). Eine Konzentration von 5% O₂, die das Wachstum w?hrend der Lagerung schon frühzeitig anregte, verursachte zu einem sp?teren Zeitpunkt eine deutliche Hemmung; diese Beeinflussung zeigte sich bei Knollen, die vorher bei 2 oder 4 C gelagert wurden, früher als bei solchen, bei denen die Lagertemperatur 10 C betrug (Tabelle 1). Es wird darauf hingewiesen, dass zwei Wirkungen des Sauerstoffes erkennbar sein dürften, n?mlich ein optimal anaerober reversibler Stoffwechsel eines Wachstumshemmstoffes sowie aerobe Voraussetzung für das Wachstum. Es werden die M?glichkeiten diskutiert, wonach bei der erstgenannten Wirkung das beteiligte Enzymsymstem von Sulphydryl abh?ngig w?re und die Reaktionsrichtung eine Parallelit?t zur Saccharoseakkumulation in der Knolle zeigen k?nne.

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Résumé On a déterminé le début de la croissance du germe, et l'importance du développement subséquent dans des concentrations en O₂ allant de 1–50%, la partie restante de l'atmosphère étant N₂, le CO₂ étant absent. On a calculé les concentrations intercellulaires en O₂ correspondant aux différentes concentrations externes. On a enregistré le pourcentage du poids des germes, le nombre de germes mesurables (> 1 mm), la longueur moyenne et la largeur du plus long germe par tubercule (Tableau 1, 2 et 3) ainsi que la fréquence des distributions de la longueur des germes dans les populations de germes (Tableaux 4, 5 et 6). Dans un essai on a mesuré la progression de la croissance du germe le plus long sur chaque tubercule, dans quatre observations successives pendant la période de stockage (Fig. 1). Chez les tubercules qui apparemment étaient encore dormants au début de l'expérience, la croissance démarrait plus t?t dans 5% O₂ que dans l'air. La concentration externe en oxygène dans laquelle le plus grand nombre de bourgeons commen?aient à se développer à 10–20 C augmentait pendant la période de stockage de 2–4% en janvier à 14–23% en juin (Tableaux 2 et 3). Il y avait une progression semblable dans la concentration optimale pour la vitesse de croissance soutenue du germe, de 4–5% à 17–20% (Tableaux 2 et 3). Le taux de 5% O₂, qui stimule le développement précoce pendant la période de stockage, cause une suppression marquée tard dans la saison, cet effet se marquant plus t?t chez les tubercules préalablement emmagasinés à 2 ou 4 C que chez ceux emmagasinés à 10 C (Tableau 1). L'auteur suggère qu'on peut discerner deux effets de l'oxygène, comprenant un métabolisme réversible idéalement anaérobie d'un inhibiteur de croissance, et une exigence aérobie de croissance. Il examine les possibilités que le système d'enzymes concernées dans le premier effet puisse dépendre du sulphydril, et que la direction de la réaction puisse montrer un parallélisme avec l'accumulation de sucrose dans le tubercule.

     

Growth rate and carbohydrate metabolism of potato tubers exposed to high temperatures

Summary The effect of high tuber temperature (30 °C) on the growth rate and carbohydrate metabolism of tubers was studied with 3 cultivars differing in heat tolerance. Subjecting individual tubers to 30°C for 6 days caused cessation of tuber growth. During this period, non-treated tubers (20°C) on the same plant increased in volume. At 30°C, incorporation of¹⁴C-labelled assimilates into the ethanol-insoluble fraction (mainly starch) as well as the starch content was significantly reduced. In contrast, the incorporation of¹⁴C-labelled assimilates into the sugar fraction was not affected by high tuber temperature. At 30°C the activity of some of the enzymes involved in starch metabolism was depressed. Varietal differences in responses of tuber growth rate and carbohydrate metabolism to high tuber temperature were insignificant. From these preliminary results it is concluded that high soil temperatures may decrease starch content of potato tubers directly by inhibition of the conversion of sugars into starch.     

The effect of storage factors on membrane permeability and sugar content of potatoes and decay byErwinia carotovora var.atroseptica andFusarium roseum var.Sambucinum

Russet Burbank and WC230-14 potato tubers were stored at 0 C (32 F) and 5 C (41 F) in air, air plus 4% CO₂ and air plus 8% CO₂ for a 175 day storage period. Four times during this period, tubers were removed and inoculated withErwinia carotovora var.atroseptica (van Hall) Dye orFusarium roseum var.sambucinum (L. K.) Sn. and H. and stored at 17 C (62.6 F). Tuber samples were also reconditioned for two weeks at 17C(62.6 F) and then inoculated. Tubers were evaluated for rate of membrane permeability, free glucose, free fructose, and sucrose content and the rate of tuber decay by the two pathogens. Relative to 5 C (41 F), 0 C (32 F) storage increased sugar content, membrane permeability and the rate of tuber breakdown. Increasing CO₂ during storage at 0 C (32 F) and 5 C (41 F) increased each of the above parameters. Reconditioning tended to alleviate the adverse effects of 0 C (32 F) storage and increasing CO₂ levels, but varietal differences existed. A significant and high correlation was obtained between the rate ofErwinia decay, membrane permeability, and sucrose content of the tubers.     

Detecting resistance to the root-knot nematodesMeloidogyne hapla andM. chitwoodi in potato and wildSolanum spp.

Summary Various methods of screening for resistance to root-knot nematodes were compared and evaluated. Seedling populations ofSolanum spp., grown in clay pots and plastic tubes with silver sand and inoculated with juveniles ofMeloidogyne chitwoodi andM. hapla, showed large differences in the number of egg masses on roots 7 weeks after inoculation. The differences were reproducible when re-testing was done with cuttings and plants from tubers. No resistance toMeloidogyne spp. was observed with ten potato cultivars when grown in clay pots, plastic tobes or closed containers. Plants from tubers in growth pouches developed a large two-dimensional root system, and after inoculation with juveniles the infection process could be observed over 8 weeks. A method of infecting potato tuber tissue withMeloidogyne is described, using tuber slices in Petri dishes as a potential screening test for tuber resistance.     

Effects of relative humidity,oxygen, and carbon dioxide on initiation and early development of stolons and tubers

Russet Burbank potatoes were grown in the greenhouse to explore the effects of soil O₂, CO₂, and relative humidity on tuberization. The composition of the gas phase surrounding the below ground stem and stolons was controlled at various levels. Prolonged levels of CO₂ greater than 5% produced large lenticels and, in combination with high relative humidity suppressed the number of stolons. Oxygen levels of 5% or less in prolonged contact with the stolons and underground portion of the stem were favorable to stem decay by pathogens but did not affect lenticel size. Isolating the stolons in a low relative humidity environment delayed tuber set, but increased the number of tubers per plant. This effect of low humidity suggests that the onset of tuberization involves at least two inductive factors, one of which is not translocated among stolons.     

The respiration of developing potato tubers

Summary The rate of O₂-uptake and CO₂-output, at 10°C., of tubers (var.Majestic) soon after they were formed at the end of June was about 50 ml/kg/hr, and fell during development to final values, before the death of the foliage, of the order of 4–5 ml/kg/hr. The quotient CO₂/O₂ remained within the range 0,85–1,19. The respiration of the tubers per plant calculated for field temperature, rose from about 6–7 ml/hr at the end of June to a peak value of 25–30 ml/hr in mid-August and thereafter fell. The results given here, coupled with observations on foliage respiration, and on the effect of temperature on respiration, suggest that increased respiration plays only a minor part in the reduction in yield which is observed at high temperatures. The mechanism of this reduction is discussed.

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Zusammenfassung Die O₂-Aufnahme und CO₂-Abgabe bei 10°C durch Knollen der SorteMajestic belief sich kurz nach ihrer Bildung am Ende Juni auf ungef?hr 50 ml/kg/Std. und field w?hrend der Weiterentwicklung bis zum Absterben des Krautes auf den Endwert 4–5 ml/kg/Std. (abb, 1 und 2). Der Quotient CO₂/O₂ blieb innerhalb des Bereiches von 0,85–1,19. Die Atmung aller Knollen pro Pflanze — berechnet für Feldtemperaturen — stieg von ungef?hr 6–7 ml/Std. Ende Juni auf einen H?chstwert von 25–30 ml/Std. um Mitte August, wenn die Knollen sich ihrer maximalen Gr?sse n?herten oder sie erreicht hatten, aber immer noch mit dem Blattwerk verbunden waren. Nachher fielen die Werte für die Atmung der Knollen pro Pflanze. Die Erstellung einer Kohlenstoffbilanz ergab ungef?hr, dass in der Mitte der aktivsten Periode des Knollenwachstums im Jahr 1961 die durchschnittliche t?gliche, von der Pflanze assimilierte Menge von CO₂ etwa 14 g betrug. Davon wurden zirka 13% in die Trockensubstanz des Krautes eingebaut, etwa 7% wurden durch das Kraut veratmet und der Rest in die unterirdischen Teile abgeführt, wo weitere 2% für das Wachstum und die Atmung der Wurzeln und ungef?hr 7% für die Atmung der Knollen verbraucht wurden. Etwas mehr als 70% gelangten in die Trockensubstanz der Knollen. Die hier wiedergegebenen Resultate, verbunden mit Beobachtungen über die Wirkung der Temperatur auf die Atmung, deuten an, dass erh?hte Atmung nur von geringerer Bedeutung ist für die bei hohen Temperaturen beobachtete Verminderung des Ertrags. Die Art und Weise dieser Ertragseinbusse wird besprochen.

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Résumé Les quantités d'oxygène (O₂) absorbées et d'anhydride carbonique (CO₂) exhalées à 10°C, par des tubercules de la variétéMajestic sit?t après leur formation à la fin juin est d'environ 50 ml/kg/h; ces quantités tombent durant le développement, avant la mort du feuillage, à des valeurs finales de l'ordre de 4–5 ml/kg/h (fig. 1 et 2). Le rapport CO₂/O₂ restait dans les limites 0,85–1,19. La respiration des tubercules d'une plante, calculée à la température du champ, s'élevait de quelque 6–7 ml/h à la fin juin, à la valeur maximum de 25–30 ml/h à la mi-ao?t, au moment où les tubercules avaient atteint ou presque leur grosseur maximum mais étaient encore attachés à un feuillage en fonctionnement. Après cela, la respiration des tubercules d'une plante diminuait. Un bilan approximatif du carbone indiquait qu'à la moitié de la période la plus active de croissance du tubercule, en 1961, la quantité moyenne journalière de CO₂ assimilée par la plante était d'environ 14 g. De ceux-ci, 13% environ sont incorporés dans la matière sèche des fanes, quelque 7% sont utilisés dans la respiration des fanes, le restant étant transféré dans la partie souterraine; 2% sont alors utilisés dans la croissance et la respiration des racines, 7% environ dans la respiration des tubercules et 70% au moins sont incorporés dans la matière sèche des tubercules. Ces résultats et ceux provenant d'observations sur l'effet de la température sur la respiration suggèrent que l'accroissement de la respiration joue seulement un r?le mineur dans la réduction de rendement observée à hautes températures. Le mécanisme de cette diminution de rendement est discuté.