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.     

Influence of IAA,NAA and 2,4-D on ethylene production by potato discs (Solanum tuberosum L. cv. Red Pontiac)

Various auxins induced an increase of ethylene production by potato discs (Solarium tuberosum L. cv. Red Pontiac). 2,4-Dichlorophenoxyacetic acid (2,4-D) at 10 μM was the most effective in stimulating ethylene (C₂H₄) production. Napthaleneacetic acid (NAA) and indole-3-acetic acid (IAA) also stimulated ethylene production with optimal concentrations of 50 μM and 100 μM, respectively. The periderm of the tuber was found to produce the highest levels of C₂H₄ with sections taken toward the center of the tuber producing much lower levels. In this system, it was shown that pH 4.0 was the optimum pH tested and methionine was required.     

Hydrogen peroxide increases potato tuber and stem starch content, stem diameter, and stem lignin content

Field-grown potato plants were sprayed twice weekly, from 21 to 90 days after planting, with 5 or 50 mM hydrogen peroxide (H₂O₂) solutions. Relative to water-sprayed controls, the H₂O₂ treatments significantly enhanced tuber starch accumulation by between 6.7% and 30%, as determined by specific gravity or the anthrone spectrophotometric method. Pronounced effects of similar H₂O₂ treatments on aerial stem anatomy and starch content were also found in glasshouse experiments. H₂O₂ treated stems were up to 27% thicker than controls, mainly due to enlarged medullar parenchyma cells. Histochemical observations indicated that there were more starch grains in cortex and pith tissue of H₂O₂-treated stems. H₂O₂ also increased the number and size of xylem tracheary elements in the vascular bundles and the number of interfascicular fibers. Quantification using image analysis confirmed that stems of H₂O₂ treated plants contained up to 3.4-fold more starch and 62% more lignin. This new chemical treatment to promote starch accumulation has potential utility in potato crop production and research.     

Induction of Freezing Tolerance by the Application of Hydrogen Peroxide and Salicylic Acid as Tuber-Dip or Canopy Spraying in <Emphasis Type="Italic">Solanum tuberosum</Emphasis> L. Plants

Low temperature stress is a current challenge to plants that is associated with climate change. In plants, exposure to extreme temperatures is followed by the accumulation of reactive oxygen species, such as hydrogen peroxide (H₂O₂), leading to oxidative stress. Salicylic acid (SA) and H₂O₂ mediate the tolerance responses to stress and have been reported to induce freezing tolerance in potato microplants. The objectives of the present investigation were (1) to evaluate the short- and long-term effects of H₂O₂ and SA treatments on freezing tolerance in potato (Solanum tuberosum L.) plants grown from tubers and (2) to analyse the relationship between catalase (CAT) activity and H₂O₂ concentration associated with freezing tolerance responses. We observed the lowest freezing survival rates in 45-day-old potato plants (cv. Granate) compared to younger plants. The two treatments consisted of (1) the tuber-dip (long-term) treatment in which sprouted minitubers were saturated for 1 h in SA 10^?5 M or H₂O₂ 1 mM and planted in soil under greenhouse conditions and (2) the crop-spray (short-term) treatment in which plants 5–8 cm high were sprayed twice a week with SA 10^?5 M or H₂O₂ 1 mM until 45 days of age. In all treatments, 45-day-old plants were then exposed to ? 6?±?1 °C for 4 h. The survival rate was measured 15 days after freezing. CAT and H₂O₂ measurements were performed 1 h before and after the freezing treatment. The results showed that SA and H₂O₂ induced freezing tolerance in both the short- and long-term treatments. Survival was significantly higher in SA- and H₂O₂-treated plants than in control plants. In both the long- and short-term treatments this higher survival was associated with lower internal H₂O₂ concentrations after freezing compared with control plants and decreasing oxidative stress. SA and H₂O₂ induced different levels of CAT activity after freezing compared to that found in the control plants in the long- and the short-term treatments. These results suggest the SA and H₂O₂ function in independent pathways in terms of their induction of freezing tolerance that depends on the method the treatment was applied, by spraying the canopy or by immersion of the sprouted seed tuber.     

Potassium rate and source effects on potato yield, quality, and disease interaction

Field experiments were conducted over eleven site-years where five K rates (0, 93, 187, 280, and 373 kg K ha^?1) as KC1 or K₂SO₄ were band-applied at planting to potato (Solanum tuberosum L. ). Significant yield increases up to 332 kg K ha^?1 were observed in five of eleven site-years when soil test K ranged from 75 to 110 mg kg¹. The increase in tuber yield was associated with an increase of tuber size (170 to 370 g) and above in the US#1A category. Lack of yield response at the other site-years may be due to the high soil test K (125 to 180 mg kg^?1). Statistically significant differences in total tuber yield were not evident between the two sources of K fertilizer studied; however, there was a tendency for a significant rate x source interaction (p > 0.15) in five site-years where K₂SO₄ increased tuber yield more than KC1 at rates up to 280 kg K ha^?1. Above this rate, tuber yield decreased for K₂SO₄ but remained stable for KC1. Based on the tuber yield data and initial soil test K from the controls of each site-year, data from this study suggest that 104 mg K kg^?1 is a critical pre-plant soil test level. A reduction in specific gravity with increasing applied K was evident in most of the site-years of this study, although decreases were generally not as marked when K₂SO₄ was used. A significant decrease in hollow heart with increasing rate of K fertilization was observed in four of eleven site-years; however, statistically significant yield responses to added K were found at only one of these sites. The incidence ofRhizoctonia solani was generally not affected by K rate; however, there was a tendency in some site-years for a higher disease incidence when KC1 was used instead of K₂SO₄ Potassium rate slightly decreased stem numbers per seed piece, averaging 3.7, 3.6, 3.5, 3.4, and 3.3 across all experiments, for the 0, 93, 187, 280, and 373 kg K ha^?1 rates, respectively.     

Serrana INTA: A widely adapted,virus resistant potato cultivar from Argentina

Serrana INTA is a late maturing cultivar with smooth, white-skinned, oblong tubers of excellent appearance and uniformity. This cultivar has shown a high level of field resistance to PLRV, extreme resistance (immunity) to PVX_C and PVY^N and hypersensitivity to PVY^O. High yields, good tuber size and ability to grow under high soil temperatures characterize this widely adapted cultivar.     

Unsaponifiable lipids from haulm and tuber sprouts of potato (Solanum tuberosum L.)

Summary Fractions containing Δ⁵- and Δ⁷-sterols, 4-methyl-sterols, triterpenic alcohols, tocopherols and hydrocarbons were isolated by TLC from petroleum ether extracts of the haulm and tuber sprouts of cv Désirée. Sterol and triterpenic alcohol fractions of unsaponifiable lipids of the haulm and tuber sprouts were found to contain twelve sterols and four triterpenic alcohols, respectively. 24R-4-stigmasten-3-on, Δ⁷, Δ⁷, lanosterol, cycloeucalenol and obtisufoliol have not been identified previously in unsaponifiable lipids from haulm and sprouts. In the hydrocarbon fractions of the haulm extract, C₂₃-to C₃₃-n-parafins, C₁₉-and C₃₁-cyclohexyl hydrocarbons, C₂₂-to C₃₈-olefins and squalene were identified, and in the hydrocarbon fractions of the tuber sprouts C₁₂-to C₂₆-olefins and squalene were identified.     

Studies on the macromolecular components of nonwood available in Bangladesh

The structural feature of macromolecular component of dhaincha, cotton stalks, jute fiber, rice straw and wheat straw, which are commonly used in paper pulp production in forest deficient countries, was thoroughly studied. Lignin was isolated by classical Bjorkman method and characterized by elemental and methoxyl analysis, alkaline nitrobenzene oxidation, FTIR and ¹H NMR spectroscopy. The C₉ formulas for cotton stalks, jute fiber, dhaincha, rice straw and wheat straw were C₉H_8.95O_3.53(OCH₃)_1.00, C₉H_8.12O_4.03(OCH₃)_1.65, C₉H_8.10O_4.65(OCH₃)_1.32, C₉H_8.58O_3.74(OCH₃)_1.23 and C₉H_8.31O_3.54(OCH₃)_1.23, respectively. The alkaline nitrobenzene oxidation products showed that syringyl to vanilin ratio of these nonwood varied from 1.1 to 2.9. Jute fiber showed the highest syringyl to vanilin ratio that are consistent with C₉ formula. The β-O-4 units in these nonwood lignins had predominately erythro stereochemistry type. The crystalline structure of these nonwood cellulose was also studied using X-ray diffraction and FTIR spectroscopy. The proportions of crystallinity, crystal size were varied from plant to plant. Jute fiber showed the highest proportion of crystallinity (73.4%) and crystal size (4.2 nm). The degree of polymerization of these nonwoods cellulose has also been studied. Degree of polymerization of jute cellulose was also the highest (3875). FTIR spectroscopy showed that these nonwoods cellulose was monoclinic unit cell structure (I_β). Carbohydrate analysis showed that the main sugar component in the hydrolyzates of these nonwoods were xylose apart from glucose.     

Study of hydrogen peroxide,potato enzymes and blackspot

The rate of oxidation of tyrosine, p-cresol and catechol by potato enzyme diminished as H₂O₂ concentration increased. By contrast, the rate of oxidation of chlorogenic acid in the presence of H₂O₂ increased. Bovine catalase destroyed H₂O₂ and thus effectively prevented either H₂O₂-induced inhibition or acceleration of oxidation of the four substrates by potato enzyme. Horseradish peroxidase in the presence of H₂O₂ did not oxidize either monophenol, but oxidized both polyphenols. Possible association of H₂O₂, peroxidase and catalase with blackspot susceptibility is discussed.     

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.     

Influence of ethylene on black spot of potato tubers

Sound, hand harvested, whole potatoes were exposed to continuous flowing atmosphere containing air, air with 3 or 5% CO₂, and air with concentrations of 0.5, 1.0, and 10ppm C₂H₄ for periods of 1 to 11 days at 20°C. At 1-day intervals, potatoes were bruised and black spot development assessed. Development of black spot in potatoes exposed to C₂H₄ was equal to or less than in potatoes at harvest. The severity remained low during 3-day exposure to 1 ppm C₂H₄ and after transfer to 4 days in air, then increased. Severity of black spot increased in potatoes exposed to air, with intermediate response from exposure to air with CO₂. With an increase in sprouting, differences in black spot among treatments diminished. Less black spot developed in immature than in mature potatoes.     

Effect of seedpiece spacing and nitrogen fertilization on tuber yield, yield components, and nitrogen use efficiency parameters of two potato cultivars

The effect of seedpiece spacing on the efficiency of nitrogen (N) use by the potato crop is generally unknown. The objective of this experiment was to determine the effect of seedpiece spacing on tuber yield, yield components and N use efficiency parameters of two potato cultivars. Potato cultivars Atlantic and Shepody were grown at two rates of N fertilization (0 or 100 kg N ha^?1) and three seedpiece spacings (20, 30, or 40 cm) in 2000 to 2002. Wider seedpiece spacing increased mean tuber weight and the number of tubers per stem, but decreased total tuber yield. The higher tuber yield at the narrow seedpiece spacing was attributed to higher biomass production in combination with lower tuber specific gravity. Seedpiece spacing had no consistent effect on plant N accumulation, and therefore no consistent effect on N uptake efficiency (plant N accumulation /N supply from the soil plus fertilizer). However, a small increase in soil NO₃-N concentration in the hill at topkill at wider seedpiece spacing suggested plant N accumulation was slightly reduced at wider seedpiece spacing, but at a level that could not be detected from a plant-based measure of N accumulation. The reduced dry matter accumulation, but similar plant N accumulation, resulted in lower N use efficiency (plant dry matter accumulation / N supply) at wider seedpiece spacing. Wider seedpiece spacing also resulted in generally lower values of N utilization efficiency (plant dry matter accumulation / plant N accumulation) for the 40-cm compared with the 20- and 30-cm seedpiece spacings. Effects of seedpiece spacing on N use efficiency parameters were generally consistent across cultivars and fertilizer N rates. Wider seedpiece spacing did reduce the efficiency of N use by the potato crop; however, the magnitude of the effect was small under the conditions of this study.     

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.     

Root System Development Including Root Branching in Cuttings of Cassava with Reference to Shoot Growth and Tuber Bulking

Summary

In spite of the important role it plays for water and nutrient acquisition, information on the root system development in cassava (Manihot esculenta Grantz) is limited. To examine the root length and branching pattern with reference to shoot growth and tuber bulking, we grew cassava plants in containers under natural climatic conditions in the southern end of Sumatra Island, Indonesia. One 20-cm length cutting of cassava (cv. Ardira IV) was planted in either a plastic bucket or a wooden box. The containers, which were filled with heavy clay soil, had different sizes depending on the growing period. At 30, 60, 100, 140, 180, and 270 days after planting (DAP), both the shoot and roots were sampled for quantitative analysis. The dry weight of both shoot and roots increased rapidly with the leaf area. The axile root number, however, decreased from 60 to 140 DAP as a result of the abscission of roots emerging from the basal part of the cutting during tuber bulking. The total root length reached its maximum at 60 DAP and significantly decreased thereafter because of decay and decomposition during tuber bulking. On the other hand, the root branching either increased the branching order or retained it, as determined from a topological point of view. The root branching during the later growing period compensated for the decrease in total root length and contributed to maintain a sufficient root surface area. The surviving roots with a well-developed branching pattern could absorb water and nutrients essential for tuber bulking.     

Interaction of ethylene,oxygen and carbon dioxide in the control of fruit ripening

Ethylene production during the climacteric in many fruits, in vegetative tissue treated with IAA, and in flowers which have been emasculated, pollinated or treated with IAA applied to their stigma, increases rapidly and then returns to a low rate. In root sections exposed to IAA this timing apparently is due to the fact that the rate of ethylene production reflects the internal IAA content; the latter increases initially after auxin is applied but rapidly decreases again due to induction or activation of the enzyme systems conjugating and destroying IAA. A similar mechanism may be involved in the induction of ethylene production in fruits.In vivo ethylene is derived from methionine, possibly after the amino acid is activated to form S-adenosyl methionine, by decarboxylation of C₁, transfer of C₂ possibly as a folic acid derivative, formation of ethylene from C₃–C₄, and transfer of the S-methyl to a suitable receptor molecule.Analogue studies indicate that ethylene attaches (K_A=6×10^–10M) to a metal containing receptor by one end through a non-covalent bond. This attachment is competitively inhibited by CO₂ (K_I=4.9×10^–4M) thus explaining the ability of this gas to antagonize most biological responses to ethylene, including fruit ripening. CO₂ does not inhibit ethylene production, but may influence fruit ripening and induce certain physiological disorders by binding to metal containing enzymes such as catalase. Ethylene production is inhibited at low O₂ concentrations; the receptor has an O₂ affinity closely similar to that of cytochrome oxidase. In addition O₂ is required for ethylene action, and the kinetics best describing the situation are those in which O₂ binds to the receptor (K_S=4×10^–5M) or indirectly oxidizes it before ethylene can attach. This effect of low pO₂ is not dependent upon a respiratory inhibition for it occurs at O₂ concentrations which are not low enough to inhibit respiration and cannot be duplicated by respiratory poisons. Thus low concentrations of O₂ retard fruit ripening both by inhibiting ethylene production and action.The rate of gas exchange and hence the internal concentration of ethylene within a fruit depends upon the diffusion coefficient of ethylene in air. As this is a function of atmospheric pressure, storing fruits at a subatmospheric pressure reduces their ethylene content. In addition this condition automatically decreases the O₂ partial pressure thus greatly extending the storage life of preclimacteric fruits.

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Zusammenfassung In vegetativen Geweben, die mit IAA (-Indolessigsäure) behandelt wurden, in sterilisierten oder befruchteten Blüten, oder in solchen, bei denen die Narbe mit IAA behandelt wurde sowie in vielen Früchten während des Klimakteriums, steigt die Äthylenbildung zunächst rasch an und sinkt dann auf eine niedrige Produktionsrate ab. In Wurzelschnitten, die mit IAA behandelt wurden, spiegelt der zeitliche Verlauf der Äthylenbildung die Zusammenhänge zwischen innerer IAA-Konzentration und Äthylen-Produktionsrate wider. Nach Auxin-Applikation steigt der IAA-Gehalt zunächst an, sinkt dann jedoch wiederum rasch ab. Dieses Verhalten lässt sich mit der Induktion und Aktivierung des Enzymsystems erklären, das die IAA bindet und abbaut. Ein ähnlicher Mechanismus mag bei der Induktion der Äthylenbildung eine Rolle spielen.In vivo wird das Äthylen aus dem Methionin gebildet. Dabei erfolgt wahrscheinlich zunächst eine Überführung in das S-Adenosyl-Methionin, wonach das C₁ decarboxyliert wird. Anschliessend wird das C₂ — vermutlich als Folsäurederivat — abgespalten und das Äthylen aus dem C₃ und C₄, nach Übertragung der Methylmercapto-Gruppe auf ein geeignetes Rezeptor-Molekül, gebildet.Analoge Untersuchungen zeigen, dass sich das Äthylen mit einem Ende an einen metallhaltigen Rezeptor in Form einer nicht kovalenten Bindung anlagert (K_A=6×10^–10M). Diese Bindung wird durch das CO₂ kompetitiv gehemmt (K_I=4,9×10^–4M). Hierdurch ist die Fähigkeit des CO₂ erklärt, in sehr vielen biologischen Prozessen, einschliesslich der Fruchtreife, zum Äthylen antagonistisch zu wirken. Das CO₂ verhindert nicht die Äthylenbildung, aber es kann die Fruchtreife beeinflussen und bestimmte physiologische Störungen durch Bindung metallhaltiger Enzyme — beispielsweise der Katalase — hervorrufen. Bei niedrigen O₂-Konzentrationen ist die Äthylenbildung gehemmt. Der Rezeptor hat eine weitgehend ähnliche O₂-Affinität wie die Cytochrom-Oxidase. Darüberhinaus ist O₂ für die Wirksamkeit des Äthylen erforderlich. Die reaktionskinetischen Vorstellungen, die die Situation am besten beschreiben, sind folgende: O₂ verbindet sich mit dem Rezeptor (K_S=4×10^–5M) oder oxidiert ihn indirekt, bevor das Äthylen ihn erreichen kann. Der Effekt, den ein geringer O₂-Partialdruck hervorruft, besteht nicht in einer Atemhemmung, denn er spielt sich auf einem O₂-Konzentrationsniveau ab, das für Atemhemmungen nicht niedrig genug ist. Ausserdem kann der Effekt durch Atemgifte nicht verdoppelt (vergrössert) werden. Eine geringe O₂-Konzentration kann daher die Fruchtreife auf zwei Weisen verzögern: Senkung der Bildungsrate und Verringerung der Wirksamkeit des Äthylens.Der Umfang des Gas-Austausches und somit die Äthylen-Konzentration innerhalb einer Frucht hängen vom Diffusions-Koeffizienten von Äthylen in Luft ab. Da dieser eine Funktion des atmosphärischen Druckes ist, senkt Aufbewahrung von Früchten bei Unterdruck ihren Äthylen-Gehalt. Diese Bedingung vermindert darüberhinaus den O₂-Partialdruck, wodurch die Lagerfähigkeit von Früchten im Vorklimakterium stark erweitert wird.

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Resume La production d'éthylène pendant la phase climactérique de nombreux fruits, dans les tissus végétatifs traités à l'acide indole acétique (AIA), et dans les fleurs qui ont été émasculées, pollinisées ou traitées à l'AIA au niveau du pistil, augmente rapidement, puis s'abaisse jusqu'à une vitesse faible. Dans des sections de racines traitées à l'AIA, ce processus est apparemment dû au fait que la vitesse de production de l'éthylène reflète le contenu interne en AIA. Ce contenu augmente initialement après que l'auxine est appliquée, mais décroît rapidement à nouveau à cause de l'induction ou l'activation du système enzymatique de synthèse et de dégradation de l'AIA. Un mécanisme similaire peut être impliqué dans la production de l'éthylène dans les fruits.In vivo l'éthylène provient de la méthionine, probablement après l'activation de l'acide aminé pour former la S-adénosyl-méthionine, par décarboxylation du C1, transfer possible de C₂ comme dérivé de l'acide folique, formation d'éthylène à partir du C₃–C₄, et transfer du S-méthyl à une molécule réceptrice adéquate.Des études analogues indiquent que l'éthylène se lie (K_A=6×10^–10M) à une extrémité d'un récepteur contenant un métal, par un lien non convalent. Cette liaison est compétitivement inhibée par CO₂ (K_I=4,9×10^–4M) ce qui explique la propriété de ce gaz en tant qu'antagoniste dans la plupart des réponses biologiques de l'éthylène, y compris dans la maturation des fruits. Le CO₂ n'inhibe pas la production même d'éthylène, mais peut influencer la maturation du fruit et induire certaines perturbations physiologiques en se liant à des enzymes contenant un métal comme la catalase. La production d'éthylène est inhibée par de faibles concentrations en oxygène; le récepteur a une affinité pour l'oxygène très proche de celle de la cytochrome oxydase. En outre, l'oxygène est nécessaire à l'action de l'éthylène, et les cinétiques décrivant le mieux la situation sont celles dans lesquelles l'oxygène se lie au récepteur (K_S=4×10^–5M) ou oxyde celui-ci indirectement, avant que l'éthylène ne puisse s'y lier. Cet effet des pressions basses en oxygène ne dépend pas de l'inhibition respiratoire puisqu'il se produit à des concentrations d'oxygène qui ne sont pas assez faibles pour inhiber la respiration, et puisqu'il ne peut pas être remplacé par les effets des poisons respiratoires. Donc de faibles concentrations en oxygène retardent la maturation du fruit, à la fois en inhibant la production et l'action de l'éthylène.La vitesse des échanges gazeux, et par conséquent la concentration interne d'éthylène à l'intérieur d'un fruit, dépend du coefficient de diffusion de l'éthylène dans l'air. Comme celui-ci est une fonction de la pression atmosphérique, la conservation des fruits à des pressions inférieures à celles de l'atmosphère réduit contenu en éthylène. De plus, cette condition fait automatiquement diminuer la pression partielle en oxygène, et augmente ainsi considérablement la durée de vie en conservation des fruits préclimactériques.

     

The effect of simazine and cytokinins on potato tuber protein,nitrogen content and yield1,2

Summary Experiments were conducted on potted potato plants to evaluate the potential of simazine and cytokinins to increase tuber protein content. Foliar sprays with higher concentrations of simazine (2 to 4 mg per litre) decreased yield. Repeated applications during tuber development tended to increase tuber nitrogen content; however, large increases in nitrogen were difficult to reproduce. Weekly applications of simazine (150 ml of 0.025 to 0.2μM) to the soil during tuberization and tuber development did not increase tuber nitrogen or protein, but tended to increase yields. A single soil application of SD 8339³, kinetin or benzyladenine did not increase tuber nitrogen or protein. These methods of simazine and cytokinin application do not appear practical as a means of increasing potato tuber protein content. This research was supported in part by a grant from the Rockefeller Founcation. Scientific Journal Series Article 8665 of the Minnesota Agricultural Experiment Station.     

Potato response to split nitrogen timing with varying amounts of excessive irrigation

Irrigation and nitrogen management are two of the most important factors affecting production efficiency and environmental quality in potato cropping systems. Field studies were conducted in 1990 and 1991 to determine the interactive effects of irrigation amount and N timing on potato yield, quality and nitrate leaching potential. Sprinkler irrigation was applied at approximately 1.0, 1.2 or 1.4 times estimated evapotranspiration (ET) to Russet Burbank potatoes grown on a silt loam soil. Following tuber initiation, a total of 132 kg N/ha was applied through the irrigation system to N treatment subplots using either six weekly 22 kg N/ha applications or 3 biweekly 44 kg N/ha applications. Excessive irrigation reduced root zone and petiole NO₃-N concentrations during substantial portions of the tuber bulking period. Biweekly 44 kg N/ha applications in 1991 produced higher and more consistent earlyseason root zone NO₃-N concentrations in the 1.2 and 1.4 ET plots than did the weekly 22 kg N/ha applications. Late-season tuber dry weight, total plant dry weight and plant N uptake were not affected by irrigation rate or N timing. However, excessive irrigation reduced U.S. No. 1 yield and yield of tubers >284 g in both 1990 and 1991 and reduced total yield in 1990. Biweekly N applications produced higher U.S. No. 1 yields than weekly N applications at all irrigation levels. Excessive irrigation also reduced NO₃-N remaining in the top 60 cm of soil at the end of the growing season. These results show that irrigating at optimal rates and applying split N at two week intervals on a silt loam soil can maximize Russet Burbank yield and quality while minimizing NO₃-N losses.     

Differential ozone susceptibility of Centennial Russet and White Rose potato as demonstrated by fumigation and antioxidant treatments

Because quantitative field estimates of potato (Solarium tuberosum L.) yield losses attributable to ozone (O₃) air pollution damage in California need to be assessed, the antioxidant compound N-[-2-(2-oxo-l-imidazolidiny l)ethyl]-N′-phenylurea (EDU or DPX-4891) was evaluated for suitability in estimating these yield losses and in differentiating O₃-susceptible from O₃-resistant cultivars. Differential susceptibility of two cultivars, ‘Centennial Russet’ (O₃sensitive) and ‘White Rose’ (O₃-resistant), to O₃ was confirmed in greenhouse experiments. Five weekly 5-hour treatments with 25 parts per hundred million O₃ reduced tuber yield of Centennial Russet by 32% but did not reduce the yield of White Rose. In the absence of O₃ under greenhouse conditions, EDU had no observable effect on shoot dry weight, tuber number, or tuber yield of either cultivar, suggesting that EDU does not materially affect plant growth in the absence of O₃ at the treatment levels used and under the conditions herein. In field experiments conducted at the University of California at Riverside (UCR) and in commercial fields of Kern County (KC), untreated Centennial Russet and White Rose plants produced total tuber yields of 174 and 512 q/ha, respectively at UCR and 268 and 498 q/ha, respectively, at KC. At UCR, EDU applied at the highest rate—17.8 kg/ha—increased marketable and total tuber yields of Centennial Russet by 208 and 188 q/ha, respectively, and increased specific gravity by 0.013. White Rose was not affected by EDU. Averaged over four KC experiments, EDU application at 8.9 kg/ha increased Centennial Russet marketable and total tuber yields by 40 (from 214) and 45 (from 268) q/ha, respectively, whereas White Rose was not affected and averaged 398 (marketable) and 491 (total) q/ha.     

The production of growth-suppressing volatile substances by stored potato tubers

Summary The sprout-suppressing constituent(s) of the volatiles may be removed by a solution of silver sulphate in 96% H₂SO₄ or by aqueous solutions of mercuric acetate or chloride. but not by 96% H₂SO₄ alone, suggesting that they may be olefinic, ethereal and/or sulphur-containing. Ethylene may be produced in very small quantities, insufficient to be an active olefinic constituent.     

不同氮肥对污染土壤玉米生长和重金属Cu、Cd吸收的影响

采用盆栽试验研究污染红壤不同氮肥处理对玉米生长和吸收重金属Cu和Cd的影响。结果表明,尿素和硝酸钙处理玉米生物量高于低硫酸铵用量处理和对照处理。在污染土壤中施入高氮量的尿素较其他处理有利于玉米生长和降低玉米植株体内重金属含量。与对照相比,尿素和硫酸铵的施用降低土壤pH值,从而增加红壤水溶态以及盐提取态Cu、Cd含量;硝酸钙处理升高土壤的pH值,降低盐提取态Cu含量。用1.0 mol/L NH₄NO₃盐提取态或水溶态根区土壤重金属含量能够很好地预测玉米对Cu和Cd的吸收。在Cu和Cd污染的酸性土壤上种植玉米,施加高用量尿素或者低用量硝酸钙来促进玉米生长和降低重金属含量,避免硫酸铵氮肥的施用。