Sprout development and processing quality changes in potato tubers stored under ethylene: 1. Effects of ethylene concentration

Ethylene effectively inhibits sprouting of potatoes (Solanum tuberosum L.) during storage, but it often darkens fry color. The objective of the work described here was to determine if altering the concentration of ethylene applied would reduce the darkening while retaining adequate sprout inhibition. Trials were conducted over three consecutive years (1991–1992, 1992–1993, and 1993–1994). Tubers of cv Russet Burbank (ca 150–300 g) were stored at 9 C for 25 wk in closed chambers in a refrigerated room under continuous exposure to 0.4, 4, 40, or 400 µL L^?1 ethylene gas delivered with the ventilation airstream (ca 0.5 air exchanges per h, for 6 h each day). Untreated control and chlorpropham-treated (CIPC) check tubers were stored under the same conditions but without ethylene supplementation. Sprout number, length, and biomass, fry color, loss of tuber mass, disease, and dry matter content were evaluated at 5-wk intervals. Dose-dependent effects (400>40>4>0.4 µL L^?1) of ethylene on sprout growth and fry color were observed. The 400, 40, and 4 µL L^?1 ethylene treatments inhibited sprout growth as effectively as CIPC, whereas in 0.4 µL L^?1 ethylene sprouting was midway between CIPC and the untreated control. Sprout mass and maximum sprout length in all ethylene treatments were significantly lower (P<0.05) than in the untreated control. Compared with the initial value (57.3 Agtron reflectance units [ARu]), after 5 wk of storage fry color was up to 5 ARu darker in the ethylene treatments, but recovered steadily at the subsequent evaluation dates. At 25 wk of storage the fry color of tubers from the 40 and 4 µL L^?1 ethylene treatments were, however, still darker than tubers stored with CIPC. Inhibition of sprout growth was slightly more effective in the 400 and 40 µL L^?1 ethylene treatments than in 4 µL L^?1, although there were no significant differences (P<0.01) in fry color between these treatments. In comparison with the other ethylene treatments, fry color in 0.4 µL L^?1 ethylene was lighter, but inhibition of sprout growth was significantly (P<0.05) poorer. There were no differences in tuber disease incidence or dry matter content between the treatments. At 25 wk, the untreated tubers had ca 50% greater loss of tuber mass than any other treatment, attributable to their heavy sprouting. Loss of tuber mass in the ethylene treatments was not significantly different (P<0.001) from that in the CIPC treatment.     

Physiological regulation of potato tuber dormancy

At harvest, potato (Solanum tuberosum L.) tubers are dormant and will not sprout. As the period of postharvest storage is extended, tuber dormancy is broken and sprout growth commences. The loss of tuber dormancy and onset of sprout growth is accompanied by numerous biochemical changes, many of which are detrimental to the nutritional and processing qualities of potatoes. Endogenous hormones have been proposed to play a significant role in tuber dormancy regulation. The involvement of all major classes of endogenous hormones in tuber dormancy is reviewed. Based on available evidence, it is concluded that both ABA and ethylene are required for dormancy induction, but only ABA is needed to maintain bud dormancy. An increase in cytokinin sensitivity and content appear to be the principal factors leading to the loss of dormancy. Changes in endogenous IAA and GA content appear to be more closely related to the regulation of subsequent sprout growth.     

Effects of ethylene and 1-methylcyclopropene on potato tuber sprout control and fry color

The study examined the efficacy of 1-methylcyclopropene (1-MCP), an anti-ethylene compound, as a preventative treatment for ethylene-induced fry color darkening in potato (Solanum tuberosum L.) tubers, without reducing the effectiveness of ethylene as a tuber sprouting control agent. The experiment was conducted for two years with ‘Shepody’ and ‘Russet Burbank.’ Tubers of each cultivar from four separate growers received one of the following treatments: Air (control), Air + 1-MCP (1 (μL.L^-1 for 48 h), isopropyl N (3-chlorophenyl) carbamate (chloropropham; CIPC; 1% a.i. [v/v]); continuous ethylene (4 μL.L^-1) in air; continuous ethylene pre-treated with 1-MCP once; continuous ethylene pre-treated with 1-MCP and repeated monthly; and continuous ethylene pre-treated with 1-MCP and repeated bi-monthly. Treatment started after suberization and cooling to 9 C, and samples were evaluated at 3-wk (year 1) or 4-wk (years 2 and 3) intervals thereafter until April (Shepody) or June (Russet Burbank). Sprout growth (sprout fresh weight per tuber), fry color (Agtron reflectance units), tuber weight loss, incidence of disease infection and internal disorders were evaluated. Weight loss, tuber infection, and the occurrence of disorders were not affected by any of the treatments. Sprout growth was controlled by the continuous ethylene supply in both cultivars, and single or multiple additions of 1-MCP to the ethylene treatment did not affect the ethylene control of sprouting. As expected, ethylene treatment alone enhanced fry color darkening in both cultivars. In Russet Burbank tubers, fry color was not darkened in any of the ethylene + 1-MCP (once, monthly, or bimonthly) treatments. In Shepody, fry color was not darkened in the ethylene + 1-MCP monthly or bimonthly treatments, but started darkening 4 wk after exposure in the single ethylene + 1-MCP treatment. It is concluded that 1-MCP can be used to control fry color darkening induced by ethylene without blocking ethylene control of tuber sprouting. However, the number of 1-MCP applications required may vary with the cultivar, e.g., one application was sufficient in Russet Burbank but not in Shepody.     

Methods to Minimize the Effect of Ethylene Sprout Inhibitor on Potato Fry Colour

Ethylene is an effective potato (Solanum tuberosum L.) sprout inhibitor, but it often darkens fry colour. Trials were conducted over nine consecutive storage seasons to identify ethylene application methods which would mitigate darkening while retaining adequate sprout inhibition, using cv. Russet Burbank plus cvs Shepody, Asterix and Santana in some years. Tubers were stored for up to 35 weeks in closed chambers with ethylene gas delivered via the ventilation airstream. Exposure to continuous 4 μl l⁻¹ ethylene after suberization and cooling were completed was designated the ethylene check. Alternative ethylene treatments included commencing exposure either before or after suberization was completed; gradually introducing the ethylene either by a concentration gradient of eight steps over 4 or 8 weeks or by increasing the duration of exposure from 6 to 24 h per day in four weekly steps; repeatedly interrupting exposure for several hours per day or for durations of 1 or more days; and warm storage. Selected ethylene treatment combinations were applied in each year, plus untreated controls, chlorpropham-treated (CIPC) checks and ethylene checks. Sprout growth, fry colour, loss of mass and disease incidence were evaluated at regular intervals. In all cultivars and all years, the ethylene check darkened fry colour more than the other treatments. Commencing before suberization ended, gradually introducing the ethylene by either concentration or time gradient and interrupting the exposure all reduced the negative effect of ethylene sprout inhibitor on fry colour. Continuous ethylene treatments inhibited sprout growth as effectively as CIPC, except at 13 °C storage. Interruptions of 18 h and 2 or more days reduced sprout inhibition. Regardless of cultivar variations, an early start using either a concentration or time-increment gradient had the least effect on fry colour while maintaining good sprout inhibition.     

Effect of exposure time of ethylene on potato sprout development

Sprouted Russet Burbank seed potato pieces were exposed from 2 to 14 days at a low concentration of ethylene, lμl l^-1, at 20 C. The longer the initial exposure time to ethylene the greater the rate of decline in sprout growth and increase in auxiliary branch growth after removal from ethylene. Sprouts were swollen, with enlarged lenticels and had retarded root development after 6 days’ exposure to ethylene. Root growth was more sensitive to ethylene than sprout growth. The implications of the similarity of sprout growth responses to ethylene under controlled conditions and sprout growth found under stress conditions in storage and field soil are discussed.     

Using Ethylene Gas and Chlorpropham Potato Sprout Inhibitors Together

Marketplace preference for lower pesticide residues in foods has led to research to reduce the residue of chlorpropham (isopropyl N-3-chlorophenyl carbamate; CIPC), a postharvest-applied sprout inhibitor which is widely used around the globe to prevent sprouting of stored potatoes (Solanum tuberosum L.). Ethylene gas, an effective, safe and non-toxic sprout inhibitor used in several countries, sometimes has negative effects on the colour of processed potato products when used alone. Trials were conducted over 3 years using cv. Shepody (French fry) and cv. NorValley (potato chips/crisps) to determine whether a combination of these two sprout inhibitors, at reduced dosages, could inhibit sprouting while maintaining good processing colour. CIPC applied at 0, 0.1, 0.25 and 1.0 times the recommended dosage was combined with 4 μll⁻¹ of ethylene gas applied or no ethylene at all (0 ethylene), for 1 day in 4 days, for 1 day in 2 days or continuously, in a factorial design. Sprout inhibition in both cultivars was excellent at all levels of CIPC application except the 0 rate. In both cultivars, sprouting was inhibited by the continuous ethylene treatment. However, all levels of ethylene exposure except the 0 rate negatively affected processing colour in both cultivars. The darkening was dose dependent, whereby the colour was darkest in continuous ethylene and was less affected by the intermittent exposures. In continuous ethylene, the colour was progressively lighter during storage after initial darkening. Shepody tubers appeared to be more sensitive to ethylene than the NorValley tubers. In Shepody only, colour in the ethylene of 1 day in 4 days treatments was progressively darker with increasing time in storage.     

Calcium Signaling is Involved in Negative Phototropism ofRice Seminal Roots简

Calcium ions(Ca2+) act as an intracellular second messenger and affect nearly all aspects of cellular life. They are functioned by interacting with polar auxin transport, and the negative phototropism of plant roots is caused by the transport of auxin from the irradiated side to the shaded side of the roots. To clarify the role of calcium signaling in the modulation of rice root negative phototropism, as well as the relationship between polar auxin transport and calcium signaling, calcium signaling reagents were used to treat rice seminal roots which were cultivated in hydroculture and unilaterally illuminated at an intensity of 100–200 μmol/(m2·s) for 24 h. Negative phototropism curvature and growth rate of rice roots were both promoted by exogenous CaCl2 lower than 100 μmol/L, but inhibited by calcium channel blockers(verapamil and LaCl3), calcineurin inhibitor(chlorpromazine, CPZ), and polar auxin transport inhibitor(N-1-naphthylphthalamic acid, NPA). Roots stopped growing and negative phototropism disappeared when the concentrations increased to 100 μmol/L verapamil, 12.500 μmol/L LaCl3, 60 μmol/L CPZ, and 6 μmol/L NPA. Moreover, 100 μmol/L CaCl2 could relieve the inhibition of LaCl3, verapamil and NPA. The enhanced negative phototropism curvature was caused by the transportation of more auxin from the irradiated side to the shaded side in the presence of exogenous Ca2+. Calcium signaling plays a key role as a second messenger in the process of light signal regulation of rice root growth and negative phototropism.     

The effect of ethylene and of inhibitors of protein and nucleic acid syntheses on dormancy break and subsequent sprout growth

Summary Cycloheximide inhibited dormancy break and subsequent sprout growth of potato buds in the presence or absence of ethylene. Dormancy break was relatively insensitive to treatment with actinomycin D, in marked contrast to the inhibition observed with cycloheximide; however, sprout elongation was inhibited by actinomycin D treatment. This suggests that dormancy release may depend on protein synthesis but not on nucleic acid synthesis. Total protein analysis revealed that two high molecular weight polypeptide bands appeared during dormancy break in the presence or absence of ethylene. The response was consistent in the two cultivars used in this study. Cycloheximide treatment blocked the synthesis of any new polypeptides in response to ethylene in the tuber tissue. This indicates that dormancy release of potato buds may be associated with the regulation of protein synthesis.     

The Influence of Plant Growth Regulators and Inflorescence Removal on Plant Growth,Yield, and Skin Color of Red LaSoda Tubers

Foliar applications of the synthetic auxin compound 2,4-dichlorophenoxyacetic acid (2,4-D) have been used to enhance skin color of red potato cultivars for many years. Relatively, little is known about the mode of action of this compound, but it has been proposed that 2,4-D stimulates ethylene production and enhances the activity of enzymes involved in anthocyanin biosynthesis. The objective of this study was to compare several other plant growth regulators to 2,4-D for their effect on plant growth, tuber yield, and skin color of the light red-skinned cultivar “Red Lasoda.” Trials were conducted in 2010 and 2011 to evaluate the effects of foliar applications of the ethylene-stimulating growth regulator ethephon, the ethylene-inhibitor 1-methylcyclopropene (1-MCP), and 2,4-D. Manual inflorescence removal was also included as a treatment to determine the influence of anthocyanin sink competition between tubers and flowers on tuber skin color. Ethephon application caused floral abscission in treated plants and reduced plant height compared to other treatments and the non-treated control. While 2,4-D caused foliar injury and ethephon slightly increased the yield of <56 g tubers, neither growth regulator affected total and marketable yield. Both ethephon and 2,4-D increased tuber skin color at harvest compared to the non-treated control. In contrast, 1-MCP and inflorescence removal had no effect on yield, tuber size, and skin color. The results indicate that ethephon and 2,4-D foliar applications have similar effects on skin color and appearance, supporting the hypothesis that 2,4-D works by stimulating ethylene production within the plant.     

Heat inhibition of tuber development in potato (Solanum tuberosum L.): effects on microtuber formation in vitro

Summary Microtuber formation by single node stem segments of in vitro grown potato plantlets was used as a model system for investigation of heat inhibition of tuber development. The stem segments were incubated in darkness at 20°C or 26°C on a tuberisation medium containing benzyl aminopurine (140 μg 1⁻¹) and sucrose (80 g 1⁻¹). Continuous incubation at 26°C strongly inhibited tuberisation and exposure to 26°C for only 1 week before transfer to 20°C significantly reduced microtuber fresh weight. Inclusion of a gibberellin synthesis inhibitor, paclobutrazol (10⁻⁵ M), in the tuberisation medium counteracted the heat inhibition of tuber initiation but not the reduction of microtuber fresh weight. Thus, consistent with previous reports, inhibition of tuber initiation appears attributable to increased endogenous levels of gibberellins. Possible causes of the reduction in microtuber fresh weight are discussed.     

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.     

Growth-room and field studies with seed tubers treated with ethylene and 1-methylcyclopropene (1-MCP) during storage

Based on ethylene management in potato storage, we hypothesized that the applied treatments would modify number of sprouts per seed tuber. Thus, in combination with in-row spacing (closer for seed, wider for processing) in the field treatments will give either (1) a high number of small tubers destined for seed use, or (2) a relatively smaller number of large, uniform tubers suitable for processing. A three-year study (2001–2003), conducted with two french fry processing cultivars, Russet Burbank (RB) and Shepody (SH), aimed at the development of a novel modified atmosphere seed tuber storage treatment. Seed tubers were stored at 4 C from October to May of each year in a cold room under five modified atmospheric regimes: (1) air ventilation only (Control); (2) 4 µl L^?1 ethylene applied continuously beginning in November and (3) beginning in February; (4) 1 µ1 L^?1 MCP (1-methylcyclopropene) applied as a gas for 48 h only in early December followed by continuous 4 µl L^?1 ethylene and (5) MCP alone applied as above. Each year, once a month (mid-January until end of April), a number of seed tubers was taken from each storage treatment, planted to pots and grown for 4 wk in a growth-room. In these studies, shoot emergence from the ethylene-treated seeds of both cultivars occurred significantly earlier, giving higher number of stems per tuber and stolons per stem than Control and MCP treatments. Moreover, the time to emergence after planting decreased with the increased length of storage. Field studies that were conducted from the end of May (planting) until October each year, produced similar trends (although not significant atP≤0.05) and resulted in a higher number of tubers per stem. In RB at the closer in row spacing (30 cm) used for seed production, ethylene enhanced yield of smaller tubers in the 30- to 115-g and 115- to 300-g categories. The ethylene storage treatments also increased tuber number per plant, but not the total mass of harvested potatoes. The MCP treatment, in combination with the wider in-row spacing (40 cm) used for the production of processing tubers, significantly increased the percentage of large tubers (>300 g). In SH, contrary to RB, the ethylene treatments did not alter tuber size distribution and the application of MCP reduced tuber size rather than increasing it. Results from this study suggest that both ethylene and MCP can be used in seed potato storage to influence the tuber size distribution of the crop from that seed.     

Effects of auxin and calcium on phosphate partitioning in induced potato (Solanum tuberosum L.) cuttings

Summary Single-node leaf cuttings, from plants originated from apical cuttings on sprouted potato tubers (Solanum tuberosum L.), were used to study phosphate transport following hormone (IAA) and calcium treatments. Phosphate accumulation in tubers was significantly enhanced by axillary bud pretreatment with calcium followed by a subsequent treatment of the tuber formed with IAA. The results suggest that calcium may be necessary for the regulatory action of auxin on phosphate transport into the tuber.     

Dimethylnaphthalene and diisopropylnaphthalene for potato sprout control in storage: 1. Application methodology and efficacy

Dimethylnaphthalene (DMN) and diisopropylnaphthalene (DIPN) isomers applied as sprout suppressants to stored potatoes (cv. Russet Burbank) were evaluated for effects on sprout length and weight compared to chlorpropham (CIPC). One application of CIPC at 22 mg a.i. kg^-1 of tuber fresh weight (f.w.), and one or two applications of DMN and DIPN at 100, 200, and 300 mg a.i. kg^-1 f.w. were applied as thermal aerosol fogs. Two applications of DIPN at 300 mg a.i. kg^-1 f.w. were as effective as CIPC in suppressing sprout growth during ten months of storage. DMN also suppressed tuber sprout growth but was not as effective as two applications of DIPN or one application of CIPC. One application of DIPN or DMN at 300 mg a.i. kg^-1 f.w. was an effective suppressant of sprout growth on a short-term basis. Whole tuber residue analyses were also conducted. After ten months in storage, DMN and DIPN residue concentrations were equal to or less than those of CIPC.     

The Combined Effect of CO2 and Ethylene Sprout Inhibitor on the Fry Colour of Stored Potatoes (Solanum tuberosum L.)

Recently, it has been shown that the darkening of potato processing colour attributable to a trace concentration of ethylene gas is more severe when CO₂ is also elevated. In view of the increasing use of ethylene gas for sprout suppression in potato storage facilities, it was considered important to determine whether this effect also occurs at the much higher ethylene concentration used in commercial practice. Sprouting and processing colour of the French fry cultivars Russet Burbank, Shepody and Innovator and the potato crisp cultivar Dakota Pearl were tested during the November to June storage season of two consecutive years. Treatments were 0 or 2 kPa CO₂ and 0 or 10 μL?L^?1 ethylene in a factorial design, plus a chlorpropham check. The 0 CO₂?+?0 ethylene treatment constituted an untreated control. The ethylene exposure was commenced abruptly to maximize its effect on colour. The main effect of ethylene resulted in darker processing colour in all cultivars, whereas darkening attributable to the main effect of CO₂ was observed only in Innovator and Dakota Pearl. The statistical interaction of the CO₂ and ethylene was not significant except in Dakota Pearl Hunter a (redness) scores, although a tendency to darker colour when both gases were present was seen in Russet Burbank and Innovator at all evaluation dates. The results indicate that both gases can affect processing colour when ethylene is used to control sprouting, although considerable variability in the response exists among cultivars. This variability in combination with management of storage conditions such as temperature and CO₂ can be utilized to minimize the impact of these gases on the processing colour of stored potatoes.     

Effect of soil salinity on internal browning of potato tuber tissue in two soil types

A study was carried out with potato (Solanum tuberosum; cv. Atlantic) during 2001 and 2002 to determine the effect of soil salinity on internal tuber browning. The effect of varying levels of soil salinity on proline content, polyphenol oxidase enzyme activity, and chlorogenic acid content in potato leaves and tubers was examined. NaCl treatments (2.1, 4.25, 6.38, 8.5 g NaCl L^?1) were applied to the pots, the first 46 days after planting, and four additional treatments were applied, each about 7 days apart. Increasing NaCl concentrations resulted in an increase in browning of tuber tissue and proline content in the tubers. Chlorogenic acid content in the leaves increased up to 6.4 g NaCl L^?1, but then decreased at 8.5 g NaCl L^?1 and in tubers tended to be maximal at the highest saline concentration tested (8.5 g NaCl L^?1). Increasing NaCl concentration resulted in a reduction in yield per plant and average tuber weight, and also increased tuber number. There were major differences in the impact of salinity over the 2-year period, which was probably due to the impact of the growing media; a low organic matter (about 1% OM) silty loam soil and a high organic content (about 90% OM) Muck soil were used in 2001 and 2002, respectively. Tuber browning increased linearly with salinity in 2002, but only markedly increased at 8.5 g NaCl L^?1 in 2001. Sodium and chloride ion concentration was always greater (about two times) at equivalent application rates in the 2002 trial. The high organic matter content soil retained sodium and chloride ions more effectively than the silty loam soil and enhanced the impact of increased salinity concentration on physiological properties of potato plants and particularly on tuber tissue browning and proline accumulation.     

Potato Stolon and Tuber Growth Influenced by Nitrogen Form

Abstract

Potato tuber initiation and its growth are key processes determining tuber yield, which are closely related to stolon growth, and are influenced by many factors including N nutrition. We investigated the influences of different forms of nitrogen (N) on stolon and tuber growth in sand culture with a nitrification inhibitor during 2010 – 2011, and using two potato cultivars. Plants supplied with NO₃-N (N as nitrate, NO₃^-) produced more and thicker stolons than those supplied with NH₄-N (N as ammonium, NH₄⁺) at tuber initiation stage. In the plants fed NO₃-N, the stolon tips swelled or formed tubers earlier and produced more tubers than in those fed with NH₄-N. However, no significant difference was observed among N forms in terms of tuber yield at harvest, this may have been because of the shoot growth rate at tuber initiation stage was lower in the plants fed NO₃-N. During the tuber bulking stage, the difference in shoot DWs among N forms began to decrease, and the shoot DW of plants fed NO₃-N was even heavier than those fed NH₄-N in some cases. The influence of N form on potato plant growth may therefore vary with the potato growth stage.     

Sprout inhibition in storage: Current status, new chemistries and natural compounds

A major component of managing potato quality in storage is effective sprout inhibition. Sprouting causes increased weight loss, reduced tuber quality and impedes air movement through the potato pile. The primary method to control sprouting in storage is with postharvest applications of isopropylN-(3-chlorophenyl) carbamate (chlorpropham; CIPC). CIPC inhibits sprout development by interfering with cell division. However, a recent Environmental Protection Agency mandate, from the requirements of the Food Quality Protection Act (FQPA) of 1996, resulted in a reduction in allowable CIPC residue on fresh potatoes in the United States from 50 ppm to 30 ppm. This mandate coincides with tolerance reductions or restrictions for use of CIPC in other parts of the world. CIPC is an effective sprout inhibitor although factors such as storage conditions, application technology, and cultivar can impact that effectiveness. Alternative sprout inhibitors to CIPC continue to be evaluated. Essential oils (e.g., caraway, peppermint, spearmint, clove) or their components (e.g., s-carvone, eugenol), and hydrogen peroxide-based materials, physically damage the developing sprout and suppress sprout elongation. However, repeated or continuous application of these compounds may be necessary for efficacy. Substituted naphthalenes (e.g., dimethyl naphthalene, diisopropyl naphthalene) may help reduce the amount of CIPC applied and/or our dependency on CIPC for sprout suppression in storage. The objective of this review is to summarize the current use of CIPC for potato sprout inhibition in storage and to review the status of current research on other postharvest applied compounds or materials that may be used as alternatives for CIPC.     

Effects of Foliar and Tuber Sprout Suppressants on Storage of Ware Potatoes under Tropical Conditions

Potato (Solanum tuberosum L.) is an important source of dietary carbohydrate and cash income generation for farmers in the tropical highlands of Kenya. The feasibility for cold storage at the farm level is limited due to the high costs of maintaining such a facility and there is limited data on the long-term post-harvest storage and quality of tubers of tropical-adapted cultivars. Application of sprout suppressants to control premature sprouting of ware potato is an attractive proposition. The objectives of this study were to evaluate the efficacy of pre-harvest foliar applications of paclobutrazol (PBZ) and ethephon for sprout suppression on ware potato tubers in storage. Post-harvest spray applications of Isopropyl N-(3-chlorophenyl carbamate) chloropropham (CIPC) and 1,4-dimethylnaphthalene (DMN) on tubers as fog was also evaluated. Potato cultivars had varying levels of tuber dormancy. The tubers were stored at ambient temperature (23 C) and evaluated weekly for 24 weeks for percent of tubers sprouting, length of longest sprouts, tuber weight loss and assessed for dormancy for 24 weeks. Paclobutrazol prolonged tuber dormancy by 21–31 days and reduced tuber weight loss. Ethephon treatment had no effect on dormancy and tuber weight loss. Potato tubers treated with CIPC had greater sprout control than the other treatments in storage. Tuber response to DMN treatment varied among the three potato cultivars evaluated. The findings from this study imply that PBZ is effective in prolonging potato tuber dormancy for short-term basis at 23 C, while CIPC applied on tubers was effective for long term storage. Optimization of post-harvest potato storage can improve food security in the highland tropics.     

Maleic hydrazide effects on tuber yield, sprouting characteristics, and french fry processing quality in various potato (Solanum tuberosum L.) cultivars grown under argentinian conditions

Field trials were carried out during 1995–1998 in commercial crops of five potato cultivars grown at several locations in Argentina to test maleic hydrazide (MH potassium salt, 36% ) effects on tuber yield, sprouting characteristics, and processing quality. MH was applied at growth stage IV, when developing tubers were 40–70 mm, at 9, 10,12 and 14 1 ha^-1 in single or split treatments. MH treatments did not produce phytotoxicity symptoms in the foliage and did not decrease tuber yield. MH increased tuber yield in Kennebec, Russet Burbank and Shepody in several experiments, while not in Atlantic and Ranger Russet. MH treatments delayed initial sprouting date and inhibited sprout growth during storage periods up to 8 months, which resulted in lower weight losses due to sprouting. Tuber dry matter content and fry color were similar or in some cases improved due to MH treatments, while no consistent results were found regarding reducing sugar content.