Tuber formation as influenced by the C : N ratio in potato plants

Increasing the tuber number per plant and promoting tuber formation are important goals for potato production. Thus, it is of significance to understand how environmental factors affect tuber formation, which relates to the development of agronomical practices. The objective of this research was to test whether changing the CO₂ or N supply level could alter the C : N ratio in potatoes, and whether a change of the C : N ratio in potatoes closely correlates with tuber formation in potato plants. Potato plantlets were grown in greenhouse with varied CO₂ or N levels. The C and N concentrations of plants were measured, and the tuber number and tuber weight were recorded after different growth times. The results show that the C : N ratios in the potato plants increased with increasing CO₂ concentration and that potato plants treated with higher CO₂ concentrations form tubers earlier. A decrease in the N supply also resulted in a higher C : N ratio and earlier tuber formation. Therefore the hypothesis proposed previously is supported by the present work. In addition, the results that C concentration in plants remained stable under different CO₂ or N levels imply that the variation of C : N ratio in the potato plants is mainly due to a change of N concentrations which decreased as the environmental CO₂ concentration increased, while increased as the N supply level increased.     

Nutrient uptake and growth of potato: Arbuscular mycorrhiza symbiosis interacts with quality and quantity of amended biochars

Aims : The aim of this study was to explore interactive effects between quality (types) and quantity (application rates) of biochar as well as of arbuscular mycorrhiza (AM) symbiosis on the growth of potato plants. Methods : A low P sandy loam soil was amended with 0%, 1.5%, or 2.5% (w/w) of either of 4 types of biochar, which were produced from wheat straw pellets (WSP) or miscanthus straw pellets (MSP) pyrolyzed at temperatures of either 550°C or 700°C. Potato plants grown in pots containing the soils or soil biochar mixture were inoculated with or without AM fungus (AMF), Rhizophagus irregularis. The experiment was carried out under fully irrigated semi‐field conditions and plants were harvested 101 days after planting. Results : Application of high temperature biochar decreased growth, biomass and tuber yield of potato plants, while the low temperature biochar had a similar effect on yield as plants grown without biochar amendment. Total biomass of potato plants were decreased with the increasing rate of biochar. Arbuscular mycorrhizal fungus inoculation stimulated the growth of potato plants in all organs, increased tuber biomass significantly in 1.5% MSP700 amended plants, and to a lesser degree for WSP700, MSP550, and WSP550. In addition, plant biomass gain was linearly related to N, P, and K uptake, the ratio of P to N in the leaf of plants indicated that all treatments were mainly P‐limited. A multiple linear regression using P uptake and biochar rate as independent variables explained 91% of the variation in total biomass. The single effect of AMF inoculation, type and rate of biochar affected plant N, P and K uptake similarly. While AMF inoculation significantly increased P uptake in potato plants grown in soil with WSP700 or MSP700 despite of the rate of biochar. In general, application of biochar significantly increased AMF root colonization of potato plants. Conclusions : The application of MSP550 at 1.5% combined with AMF stimulated growth of potato the most. Furthermore, the results indicated that the interactive effect of AMF inoculation, biochar type and application rate on potato growth to a large extent could be explained by effects on plant nutrient uptake.     

Effect of Nutritional Treatments on Physiological Characteristics and Tuberization of Potato Plants under Hydroponic Sand Culture

Under hydroponic condition, number and size of potato tubers are usually controlled by nutritional factors such as nitrogen (N), phosphorus (P), and pH. The main objective of the present study was to find an appropriate combination of N, P, and pH (with respect to tuber number) under hydroponic sand culture and to evaluate the physiological traits affected by nutrients and pH. A factorial experiment based on completely randomized design with four replications was conducted. Results showed that higher phosphorus concentration for 10 days increased tuber number per plant, but tuberization was not influenced by nitrogen interruption and intermittent reduction of pH. Neither N, P, nor pH treatments affected total nitrogen concentration of potato leaf, stem, and tuber. Higher phosphorus concentration increased the level of endogenous abscisic acid (ABA) and indole-3-acetic acid (IAA), induced tuberization and thereby increased net photosynthesis rate of potato plants.     

Micro-nutrient composition and end-user acceptable quality in potato in Ethiopia

Micronutrient deficiencies in diets, including iron (Fe) and zinc (Zn), are an important public health problem across population in Ethiopia. Potato is a modest source of dietary nutrients. The purpose of this study was to assess the mineral (Fe & Zn) composition of potato germplasm in Ethiopia and grower's willingness to try new potato types. The Fe and Zn contents were assessed in peeled tubers of popular farmer varieties, and newly introduced Andean diploid group Phureja accessions and improved tetraploid clones grown in multi-location trials. Grower's preferences for the new potato types was assessed using a participatory approach. Significant variations in mineral and tuber yield traits exist among the germplasm assessed and broad-sense heritability appears to be high for most traits measured, suggesting that progress through breeding can be made among these materials. However, the slightly negative correlation of tuber yield with Fe and Zn content and user appreciation traits found in this study suggests that progress in improving crops for yield and enhanced Fe and Zn concentrations with end-user acceptable quality will be challenging. The results from this study provide baseline information on Fe and Zn composition of many popular farmer varieties in Ethiopia and end-user preference criteria for evaluating new potato varieties that would help to orient the biofortification breeding to the conditions and preference of farmers.     

Tuber yield and allocation of nutrients and carbohydrates in potato plants as affected by limestone type and magnesium supply

Abstract

Magnesium (Mg) is a nutrient that affects the development of plants and is mainly supplied through liming performed to correct soil acidity. By acting on photosynthesis and influencing carbohydrate partitioning in the plant, supplementary Mg supplied through soil or foliar application can increase the yield and quality of potato (Solanum tuberosum L.) tubers. The aim of this study was to evaluate the effect of supplemental Mg fertilization by soil or foliar application on plant nutritional status, tuber yield, and carbohydrate partitioning in potato crops in soil corrected with calcitic and dolomitic limestones. The experiment was carried out in pots under greenhouse conditions with a randomized block design in a 2?×?3 factorial scheme with four replications. Dolomitic limestone application and supplemental Mg fertilization via soil increased the concentrations of this nutrient in potato leaves. Liming with dolomitic limestone reduced the uptake of Ca and K by plants, but supplemental Mg fertilization did not alter the uptake of Ca, Mg or K. Supplemental Mg fertilization did not increase plant growth and tuber yield, even when calcitic limestone was used to elevate the base saturation to 60%; the exchangeable Mg concentration in soil was 9?mmol_c dm^?3, and the Ca:Mg relationship was 3.7. Liming with dolomitic limestone or providing supplemental Mg fertilization did not increase sugar and starch partitioning to the tubers.     

Changes in mineral nutrient concentrations and C‐N metabolism in cabbage shoots and roots following macronutrient deficiency

The responses of metabolic networks to mineral deficiency are poorly understood. Here, we conducted a detailed, broad‐scale analysis of macronutrient concentrations and metabolic changes in the shoots and roots of cabbage (Brassica rapa L. ssp. pekinensis) plants in response to N, P, K, Ca, and Mg deficiency in nutrient solution. To standardize individual macronutrient‐deficient treatments, the concentrations of the other nutrients were maintained via substitution with other ions. Individual nutrient deficiencies had various effects on the uptake and accumulation of other mineral nutrients. Phosphorus deficiency had relatively little effect on other mineral nutrient levels compared to the other treatments. Cation deficiency had little effect on N and P concentrations but had a somewhat negative effect on the uptake or concentrations of the other nutrients. Primary metabolic pathways, such as energy production and amino acid metabolism, were greatly affected by mineral nutrient deficiency. Compared to the control treatment, soluble sugar levels increased under –N conditions and decreased under –Ca and –Mg conditions. The levels of several organic acids involved in glycolysis and the TCA cycle decreased in response to –N, –P, or –K treatment. The levels of most amino acids decreased under ‐ N treatment but increased under –P, –K, –Ca, or –Mg treatment. Mineral depletion also led to the activation of alternative biochemical pathways resulting in the production of secondary metabolites such as quinate. Notable changes in metabolic pathways under macronutrient deficiency included (1) a quantitative increase in amino acid levels in response to Mg deficiency, likely because the restriction of various pathways led to an increase in protein production and (2) a marked increase in the levels of quinate, a precursor of the shikimate pathway, following cation (K, Ca, and Mg) deficiency. These findings provide new insights into metabolic changes in cabbage in response to mineral deficiency and pave the way for studying the effects of the simultaneous deficiency of more than one macronutrient on this crop.     

Diversity studies in genetic resources of <Emphasis Type="Italic">Solanum</Emphasis> spp. (section Petota) by comparative application of ISAP markers

The Genebank at the Leibniz Institute of Plant Genetics and Crop Plant Research (IPK) harbours three different potato collections comprising 2846 wild potato accessions, 2757 accessions of cultivars, landraces and breeding material of Solanum tuberosum L. and 579 Solanum clones originating mainly from South and Central America (as of July 2016). The three collections are maintained via seeds, in vitro culture, cryopreservation or in the field. All four processes are labour and cost intensive. Therefore, methods facilitating the efficient management and maintenance of the collections are needed. We describe the experimental application of the retrotransposon-based Inter-SINE amplified polymorphism (ISAP) marker system for supporting the management of potato collections. Three ISAP primer combinations were evaluated on a set of 259 cultivated and 89 wild potato accessions focussing on three different aspects: diversity analysis, duplicate identification and phylogenetic studies. Compared to up to 29 microsatellites, ISAPs were similarly efficient in monitoring genetic diversity and detecting duplicated accessions. In addition, the three ISAP primer combinations could be applied to wild potato species, although their use in phylogenetic studies is limited due to their highly polymorphic nature. Generally, ISAPs are a very valuable tool in the maintenance of clonally maintained potato collections and for the verification of the identity of accessions.     

A Potato Collecting Expedition in the Province of Jujuy,Argentina and Disease Indexing of Virus and Fungus Pathogens in Andean Cultivars

A potato collecting expedition was carried out in the province of Jujuy, Argentina in March 24 to April 15, 2001. The objective was to collect local cultivars of potatoes and wild potato species, covering high mountain valleys not previously collected or areas where germplasm was not available. A total of 247 accessions was collected, 188 cultivated accessions of S. tuberosum subsp. andigenum, four of Solanum tuberosum subsp. tuberosum, two of S. curtilobum and 53 accessions of wild species. The wild species collected were S. acaule subsp. acaule, S. chacoense, S. infundibuliforme, S. megistacrolobum subsp. megistacrolobum, S. microdontum, S. gourlayi, S. × viirsooi and S. oplocense. Herbarium voucher specimens were obtained when possible. For the collection of cultivated potatoes, tubers were gathered from farmer's fields and in a few cases from stores or markets. Seed samples were generally obtained for the wild species. Detailed collection site data were recorded at every site. After breaking dormancy, the accessions of the cultivated species were screened for the presence of Potato virus Y (PVY), Potato virus X (PVX), Potato leafroll virus (PLRV), Potato virus S (PVS), Potato virus M (PVM), Potato virus V (PVV), Andean potato latent virus (APLV), Andean potato mottle virus (APMoV), Potato rough dwarf virus (PRDV), Potato spindle tuber viroid (PSTVd) and Spongospora subterranea f. sp. subterranea. PSTVd, APLV and PRDV were not detected, but different levels of infection are reported for the other pathogens assayed.     

Potato yield and quality under potassium and gypsum levels in southeastern Brazil

Abstract

This work was established to study the effects of sources and levels of potassium (K) along with gypsum and the residual effects of K on growth and yield of two potato (Solanum tubrosum L.) cultivars. Two experiments were conducted under field conditions at the experimental station of “Sao Sebastião do Paraíso”; Southeastern Minas Gerais, Brazil. Tuber quality, yield components, and branches and leaves mineral composition were analyzed. In the first year, using the ‘Monallsa’ cultivar, there were significant effects of treatments on plant height, tuber dry matter, and plant mineral composition. In the second year, using the ‘Achat’ cultivar, the K application plus residual gypsum from the first year reduced plant physiological anomaly known as tuber cracking.     

Critical phosphorus concentrations in potato plant parts at two growth stages

Adequately evaluating the phosphorus (P) nutritional status of a potato crop is dependent upon sampling the appropriate plant part at a defined growth stage. To establish P critical concentration levels in various potato plant parts (leaves, stems, tubers, leaflets, and petioles) at two growth stages [20 and 50 days after plant emergence (DAE)], an experiment under Brazilian climatic and soil conditions was conducted using seven P treatment levels (0, 40, 80, 160, 320, 640, and 1,280 kg P₂O₅ ha^‐1) applied in a randomized complete block design with four replications. ‘Baraka’ potato tubers were seeded at a spacing of 0.80 x 0.30 m following agronomic cultural practices recommended for this crop. Phosphorus concentrations in all the potato plant parts were significantly affected by the P fertilizer rates applied. The highest correlation between the P concentration in the various plant parts and marketable yield and optimum profit yield was obtained for the petiole taken 20 days DAE. Critical P levels associated with optimum profit yield were lower than those for maximum marketable tuber yield, and they were, 0.41, 0.39,0.39,0.57, and 0.57 g P 100 mg^‐1 DM in the leaf, stem, tuber, petiole, and leaflet, respectively.     

Evaluation of genetic resources in the genus <Emphasis Type="Italic">Asparagus</Emphasis> for resistance to <Emphasis Type="Italic">Asparagus virus 1</Emphasis> (AV-1)

Forty-four Asparagus officinalis cultivars, gene bank accessions and breeding lines as well as thirty-four accessions of wild relatives of Asparagus were evaluated for resistance to Asparagus virus 1. Three different test strategies were developed for the assessment of individual plants: (1) natural infection under field conditions, or two vector-mediated infection assays using the green peach aphid Myzus persicae (2) in an insect-proof gauze cage or (3) in a climate chamber. The AV-1 infections were verified by DAS-ELISA and RT-PCR approaches. All tested 660 individual plants of A. officinalis germplasm were susceptible to AV-1 infection. In contrast, in 276 plants of 29 Asparagus wild accessions no virus infection could be detected. These resistant accessions comprised of nineteen diploid, tetraploid and hexaploid species of both the Eurasian clade and the African clade of the asparagus germplasm. Data of the AV-1 resistance evaluation are discussed in relation to the genetic distance of the resistance carrier and potential application in breeding.     

Phosphorus and silicon effects on growth,yield, and phosphorus forms in potato plants

Silicon (Si) can increase phosphorus (P) use efficiency (PUE) by increasing P availability in the soil and altering P metabolism in the plant, thus resulting in improved yield under low soil P conditions. The objective was to evaluate the effect of P (10, 50, 100, and 200?mg dm^?3) and Si (0, 50, and 200?mg dm^?3) interrelationship on P and Si uptake by plants, forms of P in leaves and tubers, plant growth, and tuber yield of potato plants. Silicon supply increased organic and inorganic P in the leaves. At low soil P rates, Si also increased organic P in the tubers. However, alterations in the P metabolism of potato plants with Si supply did not promote significant changes in dry matter (DM) production and tuber yield. Phosphate fertilization increased growth and yield of plants. Silicon uptake by the plants were also increased by phosphate fertilization with soil Si supply.     

Genetic diversity of Bolivian wild potato germplasm: changes during ex situ conservation management and comparisons with resampled in situ populations

Potato wild relatives are important sources of novel variation for the genetic improvement of the cultivated potato. Consequently, many natural populations have been sampled and were deposited as accessions in gene banks around the world. Here we investigate to what extent the genetic variation of Bolivian wild potato species is maintained under gene bank conditions and how this diversity relates to that of current in situ populations. For this purpose, materials from seven potato species were screened for microsatellite variation. Genetic changes between different generations of ex situ germplasm were not observed for Solanum leptophyes and S. megistacrolobum, but were detected for S. neocardenasii and S. okadae, while each of the species S. acaule, S. avilesii and S. berthaultii showed stability in some cases and genetic change in others. The observed changes were ascribed to genetic drift and contamination resulting from human error during regeneration. Re-collected populations of six of the studied species showed highly significant genetic differences with the ex situ accessions that, apart from changes during ex situ maintenance, are most likely to be attributed to sampling effects during collecting and in situ genetic changes over time. The implications of the results for ex situ and in situ conservation strategies of wild potato species are discussed.     

薯麦轮作体系钾肥全部施于薯季提高甘薯和周年产量

【目的】 薯麦轮作是我国甘薯种植的主要模式,施钾对甘薯、小麦都有较好的增产效果。本文研究了薯麦轮作中钾肥最佳运筹方案,以便更好地发挥钾肥效益。 【方法】 在江苏省农业科学院位于南京的六合基地连续进行了三年田间定位试验,在周年钾肥投入总量K₂O 270 kg/hm2的前提下,设置5个甘薯 (S) /小麦 (W) 钾肥分配量处理,分别为 S0W270、S90W180、S135W135、S180W90、S270W0,重复三次。调查了产量、产量组成和生物量分配,测定了吸钾量、钾生理效率和钾表观平衡。 【结果】 钾肥分配量显著影响甘薯的块根产量、单株薯数、单个薯重、冠根比、吸钾量和钾生理效率,而对小麦产量、有效穗数、穗粒数、千粒重、草谷比、吸钾量、钾收获指数和钾生理效率均无显著影响。甘薯产量和周年产量均以钾肥全部施于薯季的S270W0处理最高,全部分配于麦季的S0W270处理次之,S270W0的甘薯产量和周年产量比薯麦两季分配的S90W180、S135W135、S180W90处理提高20.7%～24.5% (P < 0.05) 和17.8%～20.9% ( P < 0.01),S0W270的分别提高了9.9%～13.4% ( P > 0.05) 和8.2%～11.0% ( P > 0.05)。S270W0处理的单株薯数和单个薯重分别比钾肥施两季的处理高5.2%～10.4%和8.5%～30.6% ( P < 0.01),是其产量增加的主要原因;S0W270处理的单株薯数比 这三个处理高18.9%～24.8% ( P < 0.001),但单薯重低于其他处理,较高的单株薯数是该处理甘薯增产的主要原因。S180W90和S270W0处理甘薯整株吸钾量比S90W180和S0W270高出9.7%～16.1% ( P < 0.05)。随薯季施钾量增加,甘薯冠根比先增后减 ( P < 0.001)、钾生理效率先减后增 ( P < 0.01)、钾收获指数和商品率变化较小 ( P > 0.05)。甘薯吸钾量平均为K ₂O 228.0 kg/hm2,是小麦的2.3倍;钾收获指数平均为0.55,是小麦的5.5倍。薯蔓中储存的钾占甘薯吸钾量的46.6%,薯蔓还田可满足小麦对钾的需求;麦秸中贮存的钾占小麦吸钾量的91.0%,麦秸还田只能满足甘薯吸钾量的39.5%。本研究施钾量下,秸秆不还田,甘薯和小麦年均携出土壤的钾达K₂O 327.9 kg/hm2,年末土壤速效钾呈快速下降,三个轮作周期后土壤速效钾降低49.2%;秸秆和薯蔓完全还田条件下,薯麦轮作施钾量为K₂O 134.3 kg/hm2时即可保持土壤钾素平衡。 【结论】 薯麦轮作中,以钾肥单施于甘薯上,可显著增加单株薯数和单个薯重,增加甘薯产量和周年产量。全部钾肥施于甘薯上,薯蔓还田可以满足小麦的钾素营养。麦秸和薯蔓完全还田条件下,可适当减少钾肥的投入,年施K₂O 134.3 kg/hm2时即可保持钾素平衡。供试地区土壤和管理条件下,钾肥的管理模式建议为“秸秆还田 + 适宜施钾量 + 钾肥全部施于薯季”。      

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.     

Effect of various phosphorus and calcium concentrations on potato seed tuber production

Although the effects caused in plants by the calcium (Ca)–phosphorus (P) interaction in calcareous soils are well documented, very few studies report on such effects in nutritive solutions or hydroponic cultivation. In a sand and perlite (1:1 volume) hydroponic system, effects of various P (21, 42, and 63 ppm) and Ca (120, 180, and 240 ppm) concentrations on potato tuberization were studied. A factorial experiment based on a completely randomized design with three replications was conducted. For maximum tuber yield and tuber number production, 21 and 42 ppm P was sufficient, respectively. Increase in P and Ca concentrations in nutrient solutions in early growing season resulted in an increase in shoot and root weight, leaf area, and shoot length linearly, but tuber yield and tuber number did not follow this trend. The maximum tuber specific gravity and total solid percent were also observed in 42 ppm P. The highest tuber number and tuber yield were observed in 120 ppm Ca concentration.     

Biochars influence sweet‐potato yield and nutrient uptake in tropical Papua New Guinea

Currently, the biomass of an invasive and obnoxious weed, kunai grass (Imperata cylindrica), is uncontrollably burnt in Papua New Guinea in subsistence farming systems resulting in unwarranted negative environmental consequences. We explored the possibility of sustainable utilization of biochar produced from the weed biomass along with a standard feedstock‐rice husk (Oryza sativa). Biochars were produced with lab‐scale pyrolysis at 550°C, characterized for chemical properties and plant nutrient composition. Further, agronomic efficacy of soil incorporation of biochars (5 t ha^?1) or co‐applied with mineral fertilizers (100, 11, and 62 kg ha^?1 N, P, K, respectively) was tested for sweet potato (Ipomoea batatas L. Lam) in a field experiment. The two biochars differed significantly (P < 5%) with respect to recovery from the feedstocks, chemical characters and nutrient composition. Kunai grass biochar was poorer in nutrients (< 1%) with distinctly alkaline pH and higher electrical conductivity. Biochar amendment to soil showed significant (P < 5%) improvement of soil moisture, while co‐application of biochars along with mineral fertilizers showed soil moisture decrease. Biochar amendment improved the growth parameters and total tuber yield of sweet potato by about 20%, while co‐application with mineral fertilizers augmented total tuber yield by 100% and above‐ground biomass yields by > 75%. Besides, improving agronomic performance of sweet potato crop, co‐application of biochars with mineral fertilizers enhanced uptake of N, P, K, Ca, Mg, and S. Production and utilization of biochar in sweet‐potato production could offer an efficient means of disposing biomass of kunai grass with concomitant productivity improvement in Papua New Guinea.     

外生根真菌对盐渍土中油松营养成分吸收和平衡的影响

Pinus tabulaeformis seedlings were grown under a factorial design to measure biomass accumulation and P, Na and K concentrations of plants, with 3 different ectomycorrhizal fungus (EMF) strains (Boletus edulis, Xerocomus chrysenteron and Gomphidius viscidus) and two P treatments (with or without extra P). Growth and mineral nutrition of pine seedlings were stimulated by three EMF under salinity stress. Na concentrations were changed and plant K and P concentrations were increased significantly by EMF. Adding extra P made no difference in accumulation of seedlings biomass, and did not assist element absorption of plants. Although three strains of EMF can all enhance the tolerance of pine seedlings to salinity stress, they may utilize different mechanisms because of different performance in absorption of elements. The increased P and K accumulation and the balance of ion concentrations might be due to the enhanced tolerance of EMF-inoculated plants to saline conditions.     

Genetic diversity of thiamin and folate in primitive cultivated and wild potato (Solanum) species

Biofortification of staple crops like potato via breeding is an attractive strategy to reduce human micronutrient deficiencies. A prerequisite is metabolic phenotyping of genetically diverse material which can potentially be used as parents in breeding programs. Thus, the natural genetic diversity of thiamin and folate contents was investigated in indigenous cultivated potatoes (Solanum tuberosum group Andigenum) and wild potato species (Solanum section Petota). Significant differences were found among clones and species. For about 50% of the clones there were variations in thiamin and folate contents between years. Genotypes which contained over 2-fold the thiamin and 4-fold the folate content compared to the modern variety Russet Burbank were identified and should be useful material to integrate in breeding programs which aim to enhance the nutritional value of potato. Primitive cultivars and wild species with widely different amounts of thiamin and folate will also be valuable tools to explore their respective metabolic regulation.     

Critical potassium concentration and potassium/ calcium plus magnesium ratio in potato petioles associated with maximum tuber yields

In order to establish critical potassium (K) concentration levels and K/calcium (Ca) plus magnesium (Mg) [K/Ca+Mg] ratios in potato petioles associated to maximum total tuber yields, an experiment was conducted under Brazilian conditions. Six K levels (0, 60, 120, 240, 480, and 960 kg K₂O/ha as potassium sulphate) were applied in a randomized complete block design experiment with four replications. Baraka potato tubers were seeded, spaced 0.8 x 0.3 m, following the agronomic cultural practices recommended for the crop. After 48 days from plant emergence, plant tissue samples was collected from each plant, the youngest fully expanded leaves (YFEL) and the oldest but not senescent leaves (ONSL). Petioles from these leaves were analysed to their K, Ca, and Mg contents. At harvest, total, high grade, and weight tuber yields were increased to 733, 719, and 660 g/plant for the 353, 335, and 384 kg K₂O/ha levels, respectively. These yields are double the Brazilian potato yield average. Petiole Ca and Mg concentrations were decreased by the K fertilizer treatments, whereas the opposite occurred with the K/Ca+Mg ratio. Potassium concentrations in the petioles from the YFEL and ONSL increased up to 10.44 and 7.13 g K/100 g petiole dry matter at the 672 and 654 kg K₂O/ha levels, respectively. The K petiole gradient concentration was not affected by K fertilization. The K/Ca+Mg ratio for YFEL associated with the maximum total tuber yield was 7.24, while the K concentrations were 8.91 and 6.16 g K/100 g dry matter in petioles for the YFEL and ONSL, respectively.