宁夏马铃薯氮、 磷、 钾养分的吸收累积特征

【目的】马铃薯氮、 磷、 钾养分吸收累积特点国内外已有不少报道,但在宁夏地区的生产条件下尚缺乏系统研究,马铃薯配方施肥技术推广中也缺少施肥参数,难以确定合理的施肥量。因此,针对宁夏地区马铃薯种植基地的土壤条件,系统分析马铃薯干物质累积和氮、 磷、 钾养分含量,探明其对氮、 磷、 钾养分吸收累积特点,以期为马铃薯的精准施肥提供科学依据。【方法】采用田间试验和室内测定相结合的方法。于2012年分别在宁夏西吉县、 原州区、 红寺堡和同心县马铃薯种植基地进行肥料田间试验,按照当地推荐的施肥量统一施肥量和施肥方法(农家肥、 70%氮肥、 全部磷、 钾肥基施,30%氮肥在现蕾期追施),在马铃薯不同生育期采集植株样品,测定不同器官干重和氮、 磷、 钾含量,分析不同生育期马铃薯干物质累积量、 氮、 磷、 钾含量及其吸收累积量的变化特点。【结果】1)从不同种植基地来看,红寺堡区马铃薯干物质累积量最高,其次是原州区和西吉县,同心县最低;马铃薯干物质累积量随生育期的推进而增加,符合Logistic曲线,幼苗期、 块茎形成期、 块茎膨大期和淀粉累积期的干物质累积量分别占总累积量的5%、 20%、 40%和35%。2)马铃薯植株氮含量随生育期而降低,其变异系数较大; 磷、 钾含量随生育期呈先增后减的变化态势,但变异系数较小; 氮、 磷含量叶片高于其他器官,钾含量茎秆中较高。3)马铃薯氮、 磷、 钾吸收累积量在红寺堡区最高,原州区和西吉县居中,同心县最低;苗期氮、 磷、 钾的吸收量分别占全生育期总吸收量的11%、 6%、 8%,块茎形成期占28%、 23%、 31%,块茎膨大期占36%、 39%、 41%,淀粉积累期占25%、 31%、 20%;成熟期块茎中氮和磷的累积量分别占各自总累积量的60%以上,钾的累积量占50%。【结论】供试土壤条件下,马铃薯干物质累积量及养分吸收量因种植基地、 生育期和器官不同而异。从不同种植基地来看,红寺堡区马铃薯的干物质及氮、 磷、 钾累积量较高,原州区和西吉县居中,同心县最低;干物质及氮、 磷、 钾累积量随生育期的变化符合Logistic曲线,具有明显的阶段性特点,块茎膨大期累积最多,块茎形成期和淀粉积累期次之;马铃薯根、 茎和叶中吸收累积的氮、 磷、 钾占同期总累积量的比例随生育期而降低,但块茎则相反,氮、 磷、 钾吸收累积量随生育期而增加,成熟期块茎中吸收累积的养分量占全株的一半以上。     

Simplified cleanup and liquid chromatographic determination of oxamyl residues in potato tubers

A simple and efficient method is presented for the extraction, cleanup, and liquid chromatographic (LC) determination of oxamyl residues in potato tubers. Samples are extracted with methanol, partitioned into dichloromethane, and cleaned up using Sep-Pak Florisil cartridges. LC determination is performed using a Zorbax PSM 60 size exclusion column with an acetonitrile-water (1 + 9) mobile phase and UV detection at 254 nm. Recovery of oxamyl from spiked control tubers averaged 94.1 and 85.9% at fortification levels of 0.4 and 0.08 micrograms oxamyl/g tuber, respectively. The minimum detectable concentration of oxamyl by this method is 0.01 micrograms/g.     

Vermicompost and Vermiwash Minimized the Influence of Salinity Stress on Growth Parameters in Potato Plants

Potato (Solanum tuberosum L.) is the fourth major crop worldwide after cereals. Some producers use irrigation water with high salinity, which consequently decreases the agronomic yield and potato quality. The aim of this investigation was to determine the effect of vermicompost and vermiwash on plant growth and tuber yield and characteristic traits in Solanum tuberosum L. plants and tubers subjected to salinity stress. A surface response experimental design with three replicates using a central point and 15 treatments was used with vermicompost at 300, 580, and 860 g plant^?1; vermiwash at 5, 10, and 15 ml plant^?1; and salinity stress with 15, 20, and 25 mM of NaCl levels. Plant physiological measurements included plant height (cm), stem diameter (mm), and plant fresh and plant dry weight (g). Six months after planting, measurements on tuber fresh weight, pH, electric conductivity, and °Brix were carried out. The addition of vermicompost and vermiwash minimized the influence of salinity stress on growth parameters and tuber characteristics in potato plants. Vermicompost (580 g plant^?1) plus vermiwash (15 ml plant^?1) induced a greater plant height and stem diameter. Plants amended with vermicompost (860 g plant^?1), vermiwash (15 ml plant^?1), and salinity stress (15 mM) had higher pH values, whereas electrical conductivity value in potato tubers decreased.     

Influence of incorporated wild Solanum genomes on potato properties in terms of starch nanostructure and glycoalkaloid content

Interspecific somatic hybrids produced by protoplast fusion between two wild Solanum species (S. acaule, acl; S. brevidens, brd) and cultivated potato Solanum tuberosum (tbr) were analyzed in terms of the starch nanometer-range structure and glycoalkaloid (GA) contents. The crystallinity of starch granules, the average size of starch crystallites, and the lamellar distances were obtained from tuber samples using wide-angle and small-angle X-ray scattering methods. These measurements showed that incorporation of wild genomes from either nontuberous (brd) or tuberous (acl) Solanum species caused no significant modifications of the nanostructure of potato starch. In contrast, the GA profiles of the hybrids, which were analyzed by LC-ESI-MS in both tuber and foliage samples, differed considerably from those of cultivated potato. Regardless of the low total tuber GA concentrations (approximately 9 mg/100 g of fresh weight), the somatic hybrids contained GAs not detected in the parental species. A high proportion of spirotype GAs consisting of 5,6-dihydrogenated aglycons, for example, alpha-tomatine and tomatidine bound with solatriose, and chacotriose were found in the hybrids. In conclusion, the foliage of interspecific hybrids contained a higher variation in the structures of GAs than did the tubers.     

Comparison of several methods for the extraction of DNA from potatoes and potato-derived products

Eight methods were compared for the extraction of DNA from raw potato tubers, and nine methods were evaluated for the extraction of DNA from dehydrated potato slices, potato flakes, potato flour, potato starch, and two ready-to-eat potato snack foods. Extracts were assessed for yield using a fluorescence-based DNA quantification assay. Real-time amplification of an endogenous gene, sucrose synthase (sus), was used to assess extract and template quality. A CTAB-based method extracted the highest DNA yields from the tuber material. An in-house method, which utilized the Kingfisher magnetic particle processor, yielded the highest template quality from the tubers. For most of the tuber samples, the Kingfisher and CTAB methods recovered the highest levels of amplifiable sus. DNA yields for potato-derived foods generally decreased with the extent that the product had been processed. The methods that utilized the magnetic particle processor delivered the highest template quality from one of the snack products that was particularly high in fat. For most of the remaining processed products, the levels of amplifiable target DNA recovered were roughly correlated with total DNA recovery, indicating that overall yield had greater influence over sus amplification than template quality. The Wizard method was generally the best method for the extraction of DNA from most of the potato-derived foods.     

马铃薯块茎顶端优势与主茎数及产量组分的相关性

马铃薯块茎产量性状复杂,由多个产量组分构成.为探究马铃薯块茎不同顶端优势类型、植株主茎数和产量组分的相关性,本研究对国际马铃薯中心引进的102份高代品系块茎的发芽情况进行筛选,以12个顶端优势强弱程度不同的马铃薯品系为试验材料,在马铃薯植株盛花期测定主茎数;收获期统计小区产量、小区大薯产量、小区小薯产量、单株产量、单株...     

Method for the detection of synthetic cry3A in transgenic potatoes

All transgenic cultivars of potatoes registered in Canada and the United States have been modified to express a synthetic cry3A gene as a means of conferring resistance against the Colorado potato beetle, an important economic pest of potatoes. A PCR method was developed to amplify a 499 bp region of the synthetic cry3A gene. Using this method, synthetic cry3A could be detected in six different transgenic cultivars. Positive results could be confirmed with PvuII restriction digestion of the PCR-generated amplicon, which resulted in two fragments that were 283 and 216 bp in size. Of the 52 tuber extracts tested with this method, no false positive or false negative results were obtained, suggesting the method could be used with a high degree of accuracy. The absolute limit of detection was the number of cry3A copies present in one or perhaps two haploid copies of the potato genome. The practical limit of detection in tubers on a fresh weight basis was 0.02% for the NL 10-SUP and 0.01% for the remaining cultivars. Synthetic cry3A could also be detected in processed food products such as potato chips, shoestring potatoes, and frozen French fries. The method was suitable for screening potato tuber lots and some processed foods for the presence of synthetic cry3A.     

Efficiency of Nitrogen Fertilizer for Potato under Fertigation Utilizing a Nitrogen Tracer Technique

Abstract

Efficient crop use of nitrogen (N) fertilizer is critical from economic and environmental viewpoints, especially under irrigated conditions. Nitrogen fertilizer (¹⁵N‐labeled urea) and irrigation methods (drip and furrow) were evaluated on spring and fall potato cultivars under Syrian Mediterranean climatic conditions. Field experiments were conducted in the El‐Ghab Valley near Hama in fall 2000 and spring 2001 on a heavy clay soil. Four N‐fertilizer applications (70, 140, 210, and 280 kg N/ha) were applied in five equally split treatments for both irrigation methods. Potato was irrigated when soil moisture in the specified active root depth reached 80% of the field capacity as indicated by the neutron probe.

Higher marketable tuber yield of spring potato was obtained by fertigation compared to furrow irrigation; the magnitude of tuber yield increases was 4, 2, 31, and 13%, whereas for fall potato the tuber yield increases were 13, 27, 20, and 35% for N fertilizer rates of 70, 140, 210, and 280 kg N/ha, respectively. Shoot dry matter and tuber yields at the bulking stage were not good parameters to estimate marketable tuber yield. The effect of N treatments on potato yield with furrow irrigation and fertigation was limited and not significant. Drip fertigation improved tuber yield of fall potato relative to national average yield. Nitrogen uptake increased with increasing N input under both irrigation methods. Reducing N input under both irrigation methods improved N recoveries. Increasing N input significantly increased total N content in plant tissues at the bulking stage. Spring potato yields were almost double those of fall potato under both irrigation methods and all N treatments.

Nitrate (NO₃) movement in the soil solution for fall potato was monitored using soil solution extractors. Furrow irrigation resulted in greater movements of NO₃‐N below the rooting zone than drip fertigation.

Harvest index did not follow a clear trend but tended to decrease upon increasing N fertilization rates beyond 140 kg N/ha under both irrigation methods. Drip fertigation improved field water‐use efficiencies at the bulking and harvest stages. Fertigation increased specific gravity of potato tubers relative to furrow irrigation. Higher N input decreased specific gravity of potato tubers under both irrigation methods.     

Stärkegehalte von Kartoffelknollen in Abhängigkeit von Kalium-Ernährung und Knollenentwicklung

Starch content of potato tubers in relation to K nutrition and tuber growth In a pot experiment with potato (cv Saturna) K content in tubers increased from 1.0 to 2.6 % of tuber-DM due to increasing rates of K fertilizer. Simultaneously starch in tuber fresh matter decreased from 21 to 15 %. Highest starch content in tuber dry matter was obtained in that K treatment which gave the highest yield in dry tubers. Measuring starch accumulation during tuber growth revealed that already in the flowering stage differences exist in the starch contents of the tuber dry matter between the lowest and highest K treatments, namely 69 % for K₁ as compared with 64 % for K₅. The rate of starch accumulation between flowering and final harvest, however, was similar in all K treatments. This suggests that K supply affects the storage tissue at an early stage of tuber development probably via different water relations of tubers.     

Einfluß des Calcium-Angebotes auf Wachstumsrate und Calcium-Gehalt von Kartoffelknollen

Effect of calcium supply on growth rate and calcium content of potato tubers. . Using potato plants in water culture with a constant calcium supply to the roots, a study was made of the influence of additional supply of calcium to the tuber surface on growth rate and calcium content of the tubers. Under conditions of high relative humidity around the tubers the calcium nutrition of the tubers was exclusively dependent on the calcium supplied to the tuber surface (?exogenous calcium”?). With a high level of exogenous Ca the growth rate of the tubers was high and the rate of uptake of Ca was proportional to the tuber growth. With a low level of exogenous Ca the growth rate declined to a lower but constant value. In absence of exogenous supply of Ca the growth rate of the tubers declined gradually until growth ceased. Cessation of tuber growth occurred when the Ca content decreased below 0,36 mg Ca per g dry matter for smaller tubers and below 0,14 mg Ca per g dry matter for larger tubers. Severe Ca deficiency in potato tubers causes necrosis at the tuber apex.     

Genetic manipulation for enhancing calcium content in potato tuber

Increased calcium (Ca) in potatoes may increase the production rate by enhancing tuber quality and storability. Additionally, increased Ca levels in important agricultural crops may help ameliorate the incidence of osteoporosis. However, the capacity to alter Ca levels in potato tubers through genetic manipulations has not been previously addressed. Here we demonstrate that potato tubers expressing the Arabidopsis H+/Ca2+ transporter sCAX1 (N-terminal autoinhibitory domain truncated version of CAtion eXchanger 1) contain up to 3-fold more Ca than wild-type tubers. The increased Ca appears to be distributed throughout the tuber. The sCAX1-expressing potatoes have normally undergone the tuber/plant/tuber cycle for three generations; the trait appeared stable through successive generations. The expression of sCAX1 does not appear to alter potato growth and development. Furthermore, increased Ca levels in sCAX1-expressing tubers do not appear to alter tuber morphology or yield. Given the preponderance of potato consumption worldwide, these transgenic plants may be a means of marginally increasing Ca intake levels in the population. To our knowledge, this study represents the first attempts to use biotechnology to increase the Ca content of potatoes.     

Inhibition of Angiotensin converting enzyme I caused by autolysis of potato proteins by enzymatic activities confined to different parts of the potato tuber

Autolysis of protein isolates from vascular bundle and inner tuber tissues of potato (Solanum tuberosum) enhanced the inhibition of the angiotensin converting enzyme I (ACE), a biochemical factor affecting blood pressure (hypertension). The physiological age of the tuber affected the strength of ACE inhibition, the rate of its increase during autolysis, and the tuber tissue where ACE inhibition was most pronounced. The highest inhibitory activities (50% reduction in ACE activity achieved following autolysis at a protein concentration of 0.36 mg mL (-1)) were measured in tubers after 5-6 months of storage prior to sprouting. The rate of ACE inhibition was positively correlated with protease activity in tuber tissues. Amendment of the autolysis reaction with protein substrates from which bioactive ACE-inhibitory peptides may be released, for example, a purified recombinant protein or a concentrate of total tuber proteins, also enhanced ACE inhibition. Many tuber proteins including aspartic protease inhibitors were degraded during autolysis. The data provide indications of differences in the enzymatic activities confined to different parts of the potato tuber at different physiological stages. Results suggest that native enzymes and substrate proteins of potato tubers can be utilized in search of dietary tools to manage elevated blood pressure.     

Effects of different nitrogen forms on potato growth and development

The objective of this study was to test if the effects of different nitrogen forms on potato growth depend on the plant growth stage. Plants from different potato cultivars were treated with different forms of nitrogen before tuber initiation and after tuber formation. A nitrification inhibitor was used to prevent the transformation of ammonium (NH₄⁺) to nitrate (NO₃^?). Plant growth, tuber formation, leaf area, leaf chlorophyll content, and tuber yield were assessed. The results obtained over 2 years indicate that plants treated with NO₃-nitrogen (N) before or at tuber initiation produced more tubers per plant than those treated with NH₄-N. However, plants treated with NH₄-N develop tubers earlier. Additionally, after tuber formation, plants treated with NH₄-N had better shoot growth than plants treated with NO₃-N. A larger leaf area with higher leaf chlorophyll content resulted in greater dry matter accumulation and higher tuber yield at harvest for plants treated with NH₄-N.     

Characterization of the major proteins of tubers of yam bean (Pachyrhizus ahipa)

Tubers of six accessions of ahipa (Pachyrhizus ahipa) contained between 0.77 and 1.34% nitrogen on a dry weight basis. This corresponds to 4.8 to 8.4% crude protein based on a nitrogen to protein conversion factor of 6.25; but detailed analysis of AC230 showed that although 93% of the total N was extracted with buffer containing 1.0 M NaCl, about a third of this was lost on dialysis. It was calculated, therefore, that salt-soluble proteins comprise about 60% of the total tuber nitrogen, with low-molecular-mass nitrogenous components comprising a further 30%. Electophoretic analysis of the salt-soluble proteins showed similar patterns of components in the six accessions, with none being present in amounts sufficiently high to suggest a role as storage proteins. Furthermore, light microscopy failed to show significant deposits of protein within the tuber cells. Five "major" protein bands, which together accounted for about 19% of the total salt-soluble protein fraction were purified and subjected to N-terminal amino acid sequencing. Comparison of these with sequences in protein databases revealed similarities to alpha-amylases, chitinases and chitin binding proteins, cysteine proteinases (including major components from P. erosus tubers), a tuberization-specific protein from potato, and proteins induced in soybean and pea by stress or the plant hormone abscisic acid, respectively. It was concluded that the primary roles of these proteins are probably in aspects of tuber metabolism and development and/or conferring protection to pests and pathogens, and that true storage proteins are not present. The absence of storage proteins is consistent with the biological role of the tubers as storage organs for carbohydrates (cf cassava tuberous roots) rather than as propagules (cf yam and potato tubers).     

Antioxidant profiling of native Andean potato tubers (Solanum tuberosum L.) reveals cultivars with high levels of beta-carotene, alpha-tocopherol, chlorogenic acid, and petanin

The antioxidant profile of 23 native Andean potato cultivars has been investigated from a human nutrition perspective. The main carotenoid and tocopherol compounds were studied using high-performance liquid chromatography coupled with a diode array detector (HPLC-DAD) and a fluorescence detector, respectively, whereas polyphenols (including anthocyanins in colored tubers) were identified by means of both HPLC-mass spectrometry and HPLC-DAD. Antioxidant profiling revealed significant genotypic variations as well as cultivars of particular interest from a nutritional point of view. Concentrations of the health-promoting carotenoids, lutein and zeaxanthin, ranged from 1.12 to 17.69 microg g(-1) of dry weight (DW) and from 0 to 17.7 microg g(-1) of DW, with cultivars 704353 and 702472 showing the highest levels in lutein and zeaxanthin, respectively. Whereas beta-carotene is rarely reported in potato tubers, remarkable levels of this dietary provitamin A carotenoid were detected in 16 native varieties, ranging from 0.42 to 2.19 microg g(-1) of DW. The amounts of alpha-tocopherol found in Andean potato tubers, extending from 2.73 to 20.80 microg g(-1) of DW, were clearly above the quantities generally reported for commercial varieties. Chlorogenic acid and its isomers dominated the polyphenolic profile of each cultivar. Dark purple-fleshed tubers from the cultivar 704429 contained exceptionally high levels of total anthocyanins (16.33 mg g(-1) of DW). The main anthocyanin was identified as petanin (petunidin-3-p-coumaroyl-rutinoside-5-glucoside). The results suggest that Andean potato cultivars should be exploited in screening and breeding programs for the development of potato varieties with enhanced health and nutritional benefits.     

Influence of arbuscular mycorrhizal fungi on storage metabolites,mineral nutrition,and nitrogen-assimilating enzymes in potato (Solanum tuberosum L.) plant

Mycorrhizae are fungal symbionts forming mutualistic relationship with plant roots. In this study, surface-sterilized potato tubers were sown in earthen pots filled with sterile soil. Half of the pots were inoculated with sterilized arbuscular mycorrhizal fungi (AMF) spores and sterilized inoculated maize root fragments, and another half without any AMF inoculation representing control. Inoculation was done twice 3 days before sowing the tubers and on the onset of seedling emergence. Plants, along with their controls, were sampled at 20-day intervals upto 80 days after tuber initiation. The tubers of potato are shown to present a higher level of metabolites and mineral nutrition in the mycorrhizal inoculated compared to the non-inoculated. The results showed that AMF has a potential in enhancing potato production by increasing the storage metabolites, mineral nutrition in tubers and nitrogen assimilating enzymes in plant.     

Growth,Yield and Nutrition of Potato in Fumigated or Nonfumigated Soil Amended with Spent Mushroom Compost and Straw Mulch

Four cultural amendments; spent mushroom compost, straw mulch, both compost and straw mulch, or neither, were applied to soils that were either fumigated or not fumigated in a field of potatoes subject to early dying and Colorado potato beetle defoliation. Two plant samples were harvested at two week intervals to measure shoot and tuber growth and mineral nutrition, and two rows were harvested for yield at maturity. Amending the soil with compost increased vegetative growth and shoot weight more than final yield of tubers. Compost amendment delayed tuber filling by several days. Fumigation partly controlled the loss of leaf area due to early dying, but it did not increase tuber yields, and in 1994 fumigation reduced tuber yield in compost amended soils. The effects of compost and straw mulch on tuber yield were related to the concentrations of N and P in leaves. The potato crop did not benefit from compost amendment combined with fumigation, because in fumigated soil there was no improvement in plant nutrition due to compost.     

不同马铃薯品种对Cd、Pb吸收累积的差异

采用田间试验法,以中南地区主要种植的11个马铃薯品种为研究对象,测定马铃薯植株各部位重金属Cd、Pb含量,探讨不同品种的马铃薯对Cd、Pb的吸收累积差异,为马铃薯的安全种植提供实践参考。结果表明:Cd—Pb复合污染下,马铃薯块茎鲜重、茎叶鲜重以及根、茎叶、块茎中Cd、Pb含量在品种间均表现出显著差异。11个马铃薯品种块茎Cd含量范围为0.39～0.67 mg/kg,超标率100%,块茎Pb含量为0.16～0.43 mg/kg,超标率81.8%。马铃薯各部位Cd、Pb含量均呈现根茎叶块茎的分布特点;马铃薯对Cd的富集系数为2.35～5.56,对Pb富集系数为0.11～0.22,马铃薯富集转运Cd的能力大于Pb。尽管复合重金属靶标危险系数(TTHQ)法评价显示,金湘等5种马铃薯的TTHQ值1,对人体健康风险较小,但结合块茎Cd、Pb含量,建议污染区种植的马铃薯作为工业原料使用更安全。     

Fertility Response of Potato to Municipal Wastewater and Inorganic Fertilizers

This study evaluated fertilizer contribution of municipal wastewater on potato (Solanum tuberosum L.) cultivation in a split-plot experiment having two factors: water quality with 5 levels and fertilizer with 2 levels. Irrigation by raw wastewater supplied 16, 13, 13, 23, 1.7, and 83% of nitrogen (N), phosphorus (P), potassium (K), sulfur (S), zinc (Zn), and boron (B) requirement of potato, respectively. Wastewater compared to freshwater, improved plant height, vigority, area coverage, leaf area index (LAI), stem per plant, number and weight of tuber per plant, above-ground dry matter (ADM), and tuber yield of potato. Averaged over 3 years, irrigation by 75 and 100% (raw) wastewater with recommended standard fertilizers produced the maximum, but identical, tuber yield. Wastewater raised N, P, and K contents in potato plants and tubers. Irrigation by wastewater could reduce the fertilizer requirement of potato by 10–15%. However, it caused high accumulation of total coliform (TC) and faecal coliform (FC) on potato skin, restricting the use of the produce.     

Selenium species in selenium-enriched and drought-exposed potatoes

The aim of this work was to study selenium (Se) speciation in the potato ( Solanum tuberosum L.) cultivar Desiree, enriched in Se by foliar spraying with a water solution containing 10 mg of Se/L in the form of sodium selenate. Four combinations of treatments were used: well-watered plants with and without Se foliar spraying and drought-exposed plants with and without Se foliar spraying. Water-soluble Se compounds were extracted from potato tubers by water or enzymatic hydrolysis with the enzyme protease XIV, amylase, or a combination of protease XIV and amylase. Extraction was performed using incubation at a constant temperature and stirring (37 degrees C at 200 rpm) or by ultrasound-assisted extraction (300 W), using different extraction times. Separation of soluble Se species (SeCys2, SeMet, SeMeSeCys, selenite, and selenate) was achieved by ion-exchange chromatography, and detection was performed by inductively coupled plasma-mass spectrometry (ICP-MS). Results showed that the concentration of selenate extracted was independent of the enzymatic extraction technique (approximately 98 ng/g for drought-exposed and 308 ng/g for well-watered potato tubers), whereas the extraction yield of SeMet changed with the protocol used (10-36%). Selenate and SeMet were the main soluble Se species (representing 51-68% of total Se) in potato tubers, regardless of the growth conditions.