Genetic Diversity of Thiamin and Folate in Primitive ... - ACS Publications

Nov 16, 2011 - and folate contents in potato.13,14 Our previous studies have ... Table 1. Thiamin Concentrations (Mean ( SE) in Primitive and Modern P...
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Genetic Diversity of Thiamin and Folate in Primitive Cultivated and Wild Potato (Solanum) Species Aymeric Goyer* and Kortney Sweek Department of Botany and Plant Pathology, Hermiston Agricultural Research and Extension Center, Oregon State University, Hermiston, Oregon 97838, United States ABSTRACT: 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. KEYWORDS: thiamin, folate, potato tuber, Solanum tuberosum, Andigenum, wild potato species

’ INTRODUCTION Micronutrient deficiency is responsible for millions of deaths every year, especially among children, women, and the elderly of poor populations, and the death toll is very likely to increase as a result of the current economic and food crises.1,2 Several countries, including the United States, have implemented fortification of staple foods,3 leading to the eradication of severe micronutrient deficiencies. For instance, beriberi, a lethal disease due to severe thiamin deficiency, of which cases were occasionally reported as late as the 1930s, has mostly disappeared after the implementation of thiamin food fortification in 1942. Despite these measures, marginal nutritional deficiencies such as thiamin deficiency still commonly occur 4 and are often not identified because of a lack of typical symptoms, such as tachycardia, vomiting, or seizure.5 Meanwhile, many poor countries do not have the political will and the infrastructures necessary to implement food fortification, hence, micronutrient deficiencies remain common and severe in these regions. Biofortification of staple foods by breeding or biotechnology approaches is a low-cost, sustainable strategy for reducing micronutrient malnutrition occurrences.2 In particular, substantial research efforts have been made to increase vitamin contents of food crops by metabolic engineering. For instance, various projects have been aiming to increase folate content because of the deficiencies commonly occurring worldwide6,7 which are associated with the increased risk of neural tube defects (e.g., spina bifida), cardiovascular diseases, anemia, some types of cancer, and impairment in cognitive performance.8,9 Despite good success of these strategies, the general public has been rather reluctant to accept the introduction of transgenic foods in the market, thereby encouraging scientists to use other strategies more acceptable to the public, such as plant breeding. Largescale sequencing of plant genomes such as that of potato10 has facilitated breeding efforts by enabling faster and more targeted breeding strategies. While the costs associated with genome r 2011 American Chemical Society

sequencing have dropped and have enabled rapid progress, information on the natural genetic variation of micronutrients in crops remains scarce, thereby dramatically limiting advances toward nutritional enhancement. This is particularly true for the vitamins thiamin and folate, which are usually not detected or not identified in nontargeted metabolomics studies of potato.11,12 We have been exploring the natural genetic diversity of thiamin and folate contents in potato.13,14 Our previous studies have mainly focused on commercial potato varieties and advanced breeding lines. Although we found substantial variations in thiamin and folate contents (∼2.6-fold) in mature tubers, this group of germplasm represents only a small proportion of the overall genetic diversity of potatoes. Indeed, years of selection have tremendously decreased the gene pool of modern potato varieties. Indigenous cultivated (landraces) and wild (Solanum section Petota) potatoes from South and Central America, as well as the Southwestern United States, represent a tremendous genetic diversity and have been used to introgress desirable traits such as disease resistance genes15 into modern varieties. Yet, compared to the potential exploitable diversity in exotic potato combined with the number of species, it has not been fully exploited. Introduction of such material in breeding programs will help to expand the gene pool, which has been greatly restricted. The purpose of this study was to determine the range of thiamin and folate concentrations in diverse primitive cultivars and wild potato species, and to identify material which could be used as parents in breeding programs for thiamin and folate enhancement in potato. Recent studies suggest that all modern potato varieties originate from breeding with Chilean landraces from the group Chilotanum of the species S. tuberosum.16,17 Received: September 14, 2011 Accepted: November 16, 2011 Revised: November 7, 2011 Published: November 16, 2011 13072

dx.doi.org/10.1021/jf203736e | J. Agric. Food Chem. 2011, 59, 13072–13080

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Table 1. Thiamin Concentrations (Mean ( SE) in Primitive and Modern Potato Varieties concn (ng g 1) 2010a

2009 PI no./variety

clone

species

FW

FW

1021 ( 48

1272 ( 30**

5461 ( 130

1369 ( 152*

6114 ( 679

Russet Burbank

Russet Burbank

tuberosum

Russet Norkotah

Russet Norkotah

tuberosum

Yukon Gold

Yukon Gold

tuberosum

209421

RN 057.08

andigena

DW b

833 ( 241

1439 ( 145**

5337 ( 558

1315 ( 95

810 ( 110

1420 ( 28

7437 ( 149

1387 ( 106

6937 ( 528

217448

RN 061.13

andigena

1308 ( 85

225667

RN 004.06

andigena

1776 ( 47

225667

RN 004.12

andigena

1461 ( 113

1309 ( 88

7272 ( 492

225673 225677

RN 005.05 RN 008.12

andigena andigena

1555 ( 126 1444 ( 35

1176 ( 81* 1680 ( 99*

5881 ( 403c 7030 ( 415

225686

RN 010.06

andigena

1346 ( 44

1544 ( 115

9081 ( 674

225688

RN 011.03

andigena

1489 ( 104

1336 ( 206

8244 ( 1275

225689

RN 012.01

andigena

1500 ( 107

225689

RN 012.02

andigena

1401 ( 382

1959 ( 102

9993 ( 522

225689

RN 012.05

andigena

1242 ( 51

2317 ( 160**

9817 ( 677

225689

RN 012.12

andigena

1830 ( 82

1915 ( 132

10462 ( 722

225693 225693

RN 013.04 RN 013.09

andigena andigena

1231 ( 253 688 ( 83

1057 ( 79 1248 ( 37**

8739 ( 656 9313 ( 273

225694

RN 014.15

andigena

1989 ( 150

1570 ( 328

9813 ( 2048

225705

RN 017.08

andigena

1372 ( 70

1501 ( 131

8435 ( 734

225710

RN 018.03

andigena

490 ( 91

720 ( 68

4587 ( 433

234007

RN 047.05

andigena

1493 ( 30

1453 ( 25

8913 ( 152

234015

RN 049.06

andigena

968 ( 91

280868

RN 065.09

andigena

1151 ( 71

1249 ( 39

5866 ( 184

280871 280921

RN 067.01 RN 068.08

andigena andigena

1513 ( 177 1518 ( 211

1422 ( 42 1511 ( 47

6803 ( 203 7441 ( 233

280952

RN 070.01

andigena

924 ( 34

281080

RN 090.05

andigena

1657 ( 152

281080

RN 090.06

andigena

965 ( 32

1470 ( 82

6590 ( 367

1538 ( 119**

7432 ( 573

1436 ( 140

7636 ( 743

292110

RN 044.10

andigena

1202 ( 95

310490

RN 002.03

andigena

1266 ( 121

320355

RN 027.01

andigena

981 ( 28

320370 320370

RN 031.01 RN 031.14

andigena andigena

1105 ( 177 910 ( 58

607 ( 108* 1509 ( 28**

5841 ( 1040 7736 ( 123

1765 ( 34**

7415 ( 142

2325 ( 216*

12567 ( 1169

320373

RN 033.01

andigena

1503 ( 33

320373

RN 033.02

andigena

1183 ( 210

320377

RN 035.01

andigena

1766 ( 90

320377

RN 035.06

andigena

2273 ( 107

320377

RN 035.08

andigena

2179 ( 143

1084 ( 62**

9765 ( 562

320379

RN 036.05

andigena

986 ( 201

986 ( 88

8653 ( 768

320379 320379

RN 036.06 RN 036.15

andigena andigena

1888 ( 80 1828 ( 127

1260 ( 61** 1166 ( 17**

6267 ( 304 6071 ( 88

320387

RN 039.05

andigena

320390

RN 041.06

andigena

1550 ( 204

1427 ( 135

16401 ( 1554

2043 ( 272

10753 ( 1432

320390

RN 041.09

andigena

1453 ( 132

1526 ( 124

7746 ( 630

320391

RN 042.04

andigena

1395 ( 44

1127 ( 82*

5964 ( 432

320391

RN 042.14

andigena

1408 ( 23

320391

RN 042.15

andigena

1467 ( 112

2205 ( 168**

13206 ( 1007

473260 473260

RN 104.02 RN 104.05

andigena andigena

974 ( 108 1227 ( 149

1685 ( 78** 2010 ( 46**

7912 ( 367 9394 ( 213

473260

RN 104.06

andigena

1136 ( 112

1561 ( 200

7689 ( 987

13073

dx.doi.org/10.1021/jf203736e |J. Agric. Food Chem. 2011, 59, 13072–13080

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Table 1. Continued concn (ng g 1) 2010a

2009 PI no./variety 473260 473276

clone

species

RN 104.08 RN 105.01

andigena andigena

FW

FW

1492 ( 38 1154 ( 99

1788 ( 167 1377 ( 132

DW 8553 ( 798 6014 ( 578

473276

RN 105.12

andigena

1437 ( 18

1338 ( 53

6281 ( 248

473276

RN 105.14

andigena

1059 ( 67

1060 ( 31

4472 ( 131

1602 ( 82*

498171

RN 043.11

andigena

1397 ( 37

498310

RN 112.08

andigena

1361 ( 110

498310

RN 112.10

andigena

898 ( 60

707 ( 41**

7628 ( 389 2908 ( 167

a

Data for 2010 are shown on both fresh weight and dry weight bases. b Significant difference between years P < 0.01 (**) or P < 0.05 (*) as determined by Student's t test. c Dry matter content was not determined for this clone, therefore we assume 20% dry matter content.

Therefore, in an attempt to capture as much genetic diversity as possible, we focused our screening on accessions which belong to the other cultivar group in S. tuberosum, the group Andigenum. This group comprises primitive cultivars which were previously classified in the groups Phureja (diploid), Stenotomum (diploid), and Andigena (tetraploid).16

’ MATERIALS AND METHODS Potato Material. Fifty-four clones from 33 accessions of primitive cultivars (S. tuberosum group Andigenum) and three modern potato varieties were grown in the fields at NRSP6, Sturgeon Bay, WI, in 2009 and 2010. Clones were planted in a screenhouse and grown for a few weeks before being transplanted to the field in early June. These were planted as plots of five, and each plot had a border plant at each end. Tubers were harvested mid-September. One to two tubers were harvested per plant from three plants per variety (one replicate represents one plant). When tubers weighed less than 5 g, more tubers were harvested per replicate. Tubers (skin-on) were washed with water, flash-frozen in liquid nitrogen, and either directly stored in a 80 °C freezer (2009) or freeze-dried before storage at 80 °C (2010). Freeze-drying samples was added to our procedure in 2010 to allow better comparison of vitamin contents among potato clones because moisture content varied quite significantly among clones (from 74 to 91% moisture). Moisture content was calculated by weight difference before and after freezedrying potato samples. Sixty-four accessions representing 25 wild potato species were grown under glass at NRSP6, Sturgeon Bay, WI. Seeds were sown on the first of February 2010. Four seedlings of each accession were transplanted into 15 cm pots containing Pro-Mix in the greenhouse on February 15th. Tubers were harvested from mid-June to mid-July, and stored in paper sacks for five months at 6 °C under 40 to 50% humidity before processing. The samples tested were bulks of tubers from the four seedlings. Chemicals and Reagents. Folates were from Schircks Laboratories (Jona, Switzerland). Rat plasma conjugase was from Pel-Freez (Rogers, AR) and was dialyzed before use as described.18 Difco thiamin assay medium LV (TAM-LV), Difco folic acid casei medium, and Lactobacilli Broth AOAC were from Becton, Dickinson, and Company (Sparks, MD). All other chemicals were from Sigma Chemical. Bacteria. Lyophilized cultures of Lactobacillus viridescens (ATCC 12706) and Lactobacillus rhamnosus (ATCC 7469) were obtained from the American Type Culture Collection (Manassas, VA). Stock cultures of L. viridescens were prepared by stab inoculation on Lactobacilli Broth supplemented with agar, and kept in duplicate in the refrigerator. Transfers were made at monthly intervals. Glycerol-cryoprotected cells of L. rhamnosus were prepared as described previously.19

Thiamin and Folate Extraction. Potato samples (either fresh or dry) were blended into fine powder in a Waring blender. For samples harvested in 2009, 0.5 g of fresh powdered material was used for extraction. For samples harvested in 2010, 0.1 g of dried powdered material was used for extraction. Thiamin was extracted by combining acid digestion and enzymatic hydrolysis as previously described.13 Potato samples were added to 10 mL of 0.1 N HCl and autoclaved for 15 min at 121 °C. After cooling at room temperature, pH was adjusted to 4.5 by adding 1 mL of 2 N Na-acetate. Two milliliters of taka-diastase (5 mg mL 1 in 0.2 N Na-acetate pH 4.5) was added to the samples. After 18 h at 37 °C, samples were transferred to 15 mL Falcon tubes, placed on ice, and centrifuged in a swinging bucket rotor at 2700g for 5 min at 4 °C to pellet debris. The supernatants were transferred to new Falcon tubes and volumes were adjusted to 13 mL with 0.2 N Na-acetate pH 4.5. Folates were extracted by a trienzyme treatment.14 Potato samples were homogenized in 15 mL Eppendorf tubes containing 10 mL of extraction buffer (50 mM HEPES/50 mM CHES, pH 7.85, containing 2% (w/v) sodium ascorbate and 10 mM 2-mercaptoethanol, deoxygenated by flushing with nitrogen), boiled for 10 min, and cooled immediately in ice. The homogenate was treated with protease (g14 units) for 2 h at 37 °C, boiled for 5 min, and cooled immediately in ice. The sample was then treated with α-amylase (g800 units) and rat plasma conjugase in large excess (0.5 mL) for 3 h at 37 °C, boiled for 5 min, and cooled immediately in ice. After centrifugation for 10 min at 3000g, the supernatant was transferred to a new tube. The residue was resuspended in 5 mL of extraction buffer, and recentrifuged for 10 min. The combined supernatants were adjusted to a 20 mL final volume with extraction buffer, flushed with nitrogen, frozen in liquid nitrogen, and stored at 80 °C until analysis. Microbiological Assay. Thiamin and folate concentrations were measured by using a microbiological assay employing L. viridescens or L. rhamnosus, respectively, and procedures were as described previously.13,14 Assays were performed on 96-well plates (Falcon microtiter plates). Wells contained growth medium supplemented with thiamin or folate standards, or potato extracts. After ∼18 h incubation at 30 or 37 °C for thiamin or folate assays, respectively, bacterial growth was measured at 630 nm on a BioTek Instrument EL 311 SX microplate autoreader (BioTek Instrument, Winooski, VT) and analyzed with the KCJr EIA application software. Results were calculated by reference to a standard curve using thiamin or 5-formyl-THF and were expressed as nanograms of thiamin or folic acid per gram of sample. For primitive cultivars harvested in 2010, data were converted from dry to fresh weight basis to allow comparison with 2009 data. Statistical Analysis. Student's t test was used to compare thiamin and folate concentrations in potato clones between 2009 and 2010. 13074

dx.doi.org/10.1021/jf203736e |J. Agric. Food Chem. 2011, 59, 13072–13080

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Table 2. Folate Concentrations (Mean ( SE) in Primitive and Modern Potato Varieties concn (ng g 1) 2010a

2009 PI no./variety

clone

species

FW

FW

DW

Russet Burbank

Russet Burbank

tuberosum

128 ( 4

152 ( 10*

651 ( 42

Russet Norkotah

Russet Norkotah

tuberosum

158 ( 19

189 ( 16

843 ( 70

Yukon Gold

Yukon Gold

tuberosum

72 ( 20

209421

RN 057.08

andigena

248 ( 12

243 ( 24

1272 ( 124

217448

RN 061.13

andigena

102 ( 10

88 ( 5

440 ( 27

225667

RN 004.06

andigena

72 ( 9

225667

RN 004.12

andigena

140 ( 5

81 ( 11**

452 ( 63

225673 225677

RN 005.05 RN 008.12

andigena andigena

65 ( 14 117 ( 21

136 ( 10** 123 ( 4

682 ( 51c 516 ( 17

225686

RN 010.06

andigena

91 ( 8

80 ( 5

473 ( 28

225688

RN 011.03

andigena

123 ( 14

155 ( 21

956 ( 127

225689

RN 012.01

andigena

118 ( 28

225689

RN 012.02

andigena

89 ( 25

238 ( 46*

1213 ( 234

225689

RN 012.05

andigena

73 ( 9

238 ( 50**

1007 ( 212

225689

RN 012.12

andigena

130 ( 14

321 ( 15**

1754 ( 83

225693 225693

RN 013.04 RN 013.09

andigena andigena

15 ( 1 119 ( 30

85 ( 22** 158 ( 53

706 ( 180 1179 ( 395

225694

RN 014.15

andigena

128 ( 14

107 ( 33

225705

RN 017.08

andigena

121 ( 38

184 ( 18

1035 ( 99

225710

RN 018.03

andigena

108 ( 16

329 ( 32**

2098 ( 203

234007

RN 047.05

andigena

200 ( 11

83 ( 11

931 ( 428

234015

RN 049.06

andigena

198 ( 8

220 ( 16

1484 ( 108

280868

RN 065.09

andigena

83 ( 35

301 ( 21**

1412 ( 80

280871 280921

RN 067.01 RN 068.08

andigena andigena

271 ( 72 195 ( 32

235 ( 14 264 ( 14

1122 ( 63 1302 ( 68

280952

RN 070.01

andigena

209 ( 16

281080

RN 090.05

andigena

129 ( 6

174 ( 8**

780 ( 38

281080

RN 090.06

andigena

221 ( 13

231 ( 11

1118 ( 52

292110

RN 044.10

andigena

232 ( 21

310490

RN 002.03

andigena

273 ( 12

320355

RN 027.01

andigena

165 ( 19

320370 320370

RN 031.01 RN 031.14

andigena andigena

110 ( 7 79 ( 11

190 ( 17**

973 ( 88

320373

RN 033.01

andigena

125 ( 7

182 ( 14**

763 ( 59

320373

RN 033.02

andigena

164 ( 28

320377

RN 035.01

andigena

165 ( 7

211 ( 8**

1142 ( 42

320377

RN 035.06

andigena

163 ( 8

320377

RN 035.08

andigena

154 ( 11

320379

RN 036.05

andigena

68 ( 10

102 ( 8*

892 ( 70

320379 320379

RN 036.06 RN 036.15

andigena andigena

96 ( 5 103 ( 12

98 ( 36 139 ( 46

487 ( 178 725 ( 241

102 ( 14

1176 ( 164

b

187 ( 23**

99 ( 14*

720 ( 90

668 ( 208

896 ( 127

320387

RN 039.05

andigena

320390

RN 041.06

andigena

61 ( 11

74 ( 1

388 ( 8

320390

RN 041.09

andigena

113 ( 11

228 ( 39*

1157 ( 198

320391

RN 042.04

andigena

105 ( 9

99 ( 7

524 ( 39

320391

RN 042.14

andigena

109 ( 21

320391

RN 042.15

andigena

131 ( 23

147 ( 12

881 ( 74

473260 473260

RN 104.02 RN 104.05

andigena andigena

306 ( 77 148 ( 45

416 ( 23 304 ( 35*

1955 ( 107 1422 ( 166

473260

RN 104.06

andigena

148 ( 16

222 ( 9**

1095 ( 45

13075

dx.doi.org/10.1021/jf203736e |J. Agric. Food Chem. 2011, 59, 13072–13080

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Table 2. Continued concn (ng g 1) 2010a

2009 clone

species

FW

FW

DW

473260 473276

PI no./variety

RN 104.08 RN 105.01

andigena andigena

134 ( 8 180 ( 8

83 ( 17* 153 ( 17

400 ( 82 670 ( 75

473276

RN 105.12

andigena

281 ( 26

187 ( 10**

473276

RN 105.14

andigena

205 ( 14

272 ( 39

1147 ( 163

498171

RN 043.11

andigena

112 ( 33

85 ( 17

403 ( 83

498310

RN 112.08

andigena

165 ( 6

171 ( 13

702 ( 55

498310

RN 112.10

andigena

232 ( 39

876 ( 47

a

Data for 2010 are shown on both fresh weight and dry weight bases. b Significant difference between years P < 0.01 (**) or P < 0.05 (*) as determined by Student's t test. c Dry matter content was not determined for this clone, therefore we assumed 20% dry matter content.

Figure 1. Frequency of primitive and modern cultivars within thiamin concentration brackets. One-way analysis of variance (ANOVA) was carried out to compare the means of thiamin and folate concentrations among clones and among species. All statistical analyses were carried out using Statgraphics Centurion XVI.

’ RESULTS AND DISCUSSION We investigated the genetic variation of thiamin and folate in 54 primitive cultivated potatoes (S. tuberosum group Andigenum) grown in 2009 and 2010 (Tables 1 and 2). There were significant differences in thiamin and folate concentrations among clones from the same harvest as determined by ANOVA (P < 0.01 at the 95% confidence level). Thiamin and folate concentrations ranged from 490 to 2325 ng g 1 FW and from 15 to 416 ng g 1 FW, respectively (or 2908 to 16401 ng g 1 DW for thiamin and 388 to 2098 ng g 1 DW for folate in 2010). The majority of the clones had thiamin and folate concentrations in the ranges of 1200 1600 and 100 200 ng g 1 FW, respectively, in both years (Figures 1 and 2). Common commercial varieties Russet Burbank, Russet Norkotah, and Yukon Gold were among this majority of clones. For 46% of the clones, there were statistically significant differences in thiamin and folate concentrations between years (Tables 1 and 2), suggesting low genetic stability of these clones. Of particular interest are clones which have

Figure 2. Frequency of primitive and modern cultivars within folate concentration brackets.

relatively high thiamin or folate content compared to modern varieties and are stable over the years. The clone RN 035.01 (PI 320377) is a good example: in both years it contained over 13076

dx.doi.org/10.1021/jf203736e |J. Agric. Food Chem. 2011, 59, 13072–13080

Journal of Agricultural and Food Chemistry Table 3. Thiamin and Folate Concentrations (ng g PI no.

species

500047

S. acaule subsp. aemulans

243510

S. bulbocastanum

ARTICLE 1

DW ( SE) in Wild Potato species thiamin 10065 ( 37 4800 ( 273

folate

% dry matter

803 ( 12

19

815 ( 24

23

545751

S. bulbocastanum

4830 ( 304

767 ( 0

21

545964

S. boliviense

5884 ( 189

423 ( 22

30

597736

S. boliviense

4317 ( 209

3031 ( 46

28

265863

S. bukasovii

7146 ( 100

413 ( 56

17

197760

S. chacoense subsp. chacoense

6265 ( 0

347 ( 33

30

275139 320293

S. chacoense subsp. chacoense S. chacoense subsp. chacoense

4318 ( 328 5820 ( 0

207 ( 22

23 29

472837

S. commersonii subsp. commersonii

6621 ( 32

570 ( 12

24

473411

S. commersonii subsp. commersonii

5415 ( 342

260 ( 11

34

558050

S. commersonii subsp. commersonii

6784 ( 65

498232

S. demissum

7113 ( 133

457 ( 34

26 22

34

265579

S. gourlayi subsp. gourlayi

7858 ( 546

962 ( 25

473011

S. gourlayi subsp. gourlayi

8093 ( 34

864 ( 25

20

473062 251065

S. gourlayi subsp. gourlayi S. hjertingii

6784 ( 65 4710 ( 363

593 ( 35 780 ( 36

21 29

283103

S. hjertingii

5043 ( 153

1090 ( 103

26

545715

S. hjertingii

6653 ( 65

1179 ( 25

26

265867

S. infundibuliforme

6787 ( 392

614 ( 25

23

458324

S. infundibuliforme

5105 ( 277

520 ( 40

23

472894

S. infundibuliforme

6010 ( 0

1273 ( 0

23

275262

S. jamesii

6365 ( 418

1199 ( 25

42

458425 592422

S. jamesii S. jamesii

7717 ( 135 6300 ( 353

1085 ( 30 644 ( 45

33 40 23

472923

S. kurtzianum

4049 ( 177

505 ( 25

472941

S. kurtzianum

3754 ( 117

673 ( 25

23

498359

S. kurtzianum

4798 ( 91

485 ( 5

26

500041

S. microdontum

5199 ( 370

1704 ( 5

22

265873

S. megistacrolobum

5243 ( 31

817 ( 0

11

473133

S. megistacrolobum

5855 ( 0

648 ( 40

16

498383 498130

S. megistacrolobum S. okadae

5118 ( 348 5953 ( 32

564 ( 5 1015 ( 30

20 21

1099 ( 5

26

435079

S. oplocense

5467 ( 128

473185

S. oplocense

3727 ( 128

881 ( 84

29

473190

S. oplocense

2896 ( 58

527 ( 14

23

184774

S. pinnatisectum

6055 ( 460

986 ( 65

40

275236

S. pinnatisectum

4397 ( 61

513 ( 13

42

347766

S. pinnatisectum

7193 ( 0

865 ( 42

37

310953 473369

S. raphanifolium S. raphanifolium

6618 ( 369 7332 ( 207

494 ( 7 520 ( 33

27 28 22

473370

S. raphanifolium

6282 ( 33

686 ( 0

230464

S. sanctae-rosae

5470 ( 385

475 ( 52

25

205407

S. spegazzinii

5188 ( 667

417 ( 20

28

472978

S. spegazzinii

5563 ( 32

406 ( 10

22

500053

S. spegazzinii

6417 ( 366

1054 ( 16

18

473504

S. sparsipilum

5725 ( 130

503 ( 4

30

545912 597687

S. sparsipilum S. sparsipilum

5563 ( 32 6418 ( 366

853 ( 13 1207 ( 35

31 20

636406

S. stoloniferuma

6583 ( 201

1312 ( 14

29

641031

S. stoloniferuma

5953 ( 164

789 ( 13

24

643994

S. stoloniferuma

4520 ( 62

597 ( 18

26

558447

S. stoloniferumb

5520 ( 66

507 ( 12

27

558451

S. stoloniferumb

5126 ( 65

801 ( 0

26

13077

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Journal of Agricultural and Food Chemistry

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Table 3. Continued PI no.

a

species b

thiamin

folate

% dry matter

4640 ( 96 4544 ( 64

795 ( 6 950 ( 59

24 27

1143 ( 41

27

586947 275228

S. stoloniferum S. stoloniferumc

498033

S. stoloniferumc

6324 ( 0

473243

S. berthaultii

5493 ( 628

614 ( 37

22

473336

S. berthaultii

4834 ( 161

1160 ( 74

20

161173

S. verrucosum

7259 ( 35

666 ( 15

27

275255

S. verrucosum

6602 ( 412

577 ( 30

28

498062

S. verrucosum

6771 ( 173

674 ( 53

26

230468 500062

S. vernei subsp. vernei S. vernei subsp. vernei

8633 ( 111 9853 ( 351

1567 ( 8 1665 ( 54

18 19

Previously “fendleri”. b Previously “polytrichon”. c Previously “papita”.

1.7 times more thiamin on a fresh weight basis than Russet Burbank, a commonly grown russet variety, and over 2.3 times more thiamin than Russet Burbank on a dry weight basis. Because potato clones had dry matter content varying from 9 to 26%, comparing metabolite contents among clones on a dry weight basis is a better indication of the quantitative variation present among clones for these vitamins. For instance, although the clone RN 035.08 (PI 320377) had low thiamin content relative to Russet Burbank on a fresh weight basis in 2010, it had ∼1.8 more thiamin on a dry weight basis. The clone RN 035.06 (PI 320377) contained 2.2 times more thiamin than Russet Burbank on a fresh weight basis. Unfortunately, this clone did not produce tubers in 2010 and we were not able to determine whether this clone had high thiamin content over multiple years. Nevertheless, these clones had higher thiamin concentrations than any of those reported in modern potato varieties,13 and although data from additional years would be necessary to fully assess the stability of these clones, this accession (PI 320377) seems to be a promising material to integrate in breeding programs for thiamin enhancement. There were other interesting clones, such as RN 039.05 (PI 320387) which had the highest thiamin concentrations, containing three times more thiamin than Russet Burbank. The clone RN 104.02 (PI 473260) had the highest folate content with 2.4 and 2.7 times more folate than Russet Burbank in 2009 and 2010, respectively, on a fresh weight basis, and 3 times more on a dry weight basis. There was no statistically significant difference in mean folate concentrations in RN 104.02 between the two years, suggesting that this clone may be stable for folate content. Segregating clones from the same accession also had relatively high folate concentrations in 2010, except for RN 104.08, but had much lower amounts in 2009 on a fresh weight basis. Therefore, the clone RN 104.02 could be useful for folate enhancement, and caution should be taken in selecting appropriate clones among this accession. We extended our screening to 25 wild potato species comprising 64 different accessions (Table 3). There were significant differences in thiamin and folate concentrations among clones and among species as determined by ANOVA (P < 0.01 at the 95% confidence level). S. vernei subsp. vernei and S. acaule subsp. aemulans had the highest thiamin concentrations and were significantly different from all other species (Fisher’s LSD at the 95% confidence level). S. boliviense accession 597736 had the highest folate concentrations with 3031 ng g 1 DW, exceeding any folate concentrations that we have so far found in potato,20 but the other S. boliviense accession had a much lower amount, suggesting variability within species. Interestingly, in

addition to being relatively high for thiamin, S. vernei subsp. vernei also had relatively high folate concentrations. Overall, thiamin concentrations ranged from 2896 to 10065 ng g 1 DW, while folate concentrations ranged from 207 to 3031 ng g 1 DW. Although multiple year or location data will be necessary to determine the genetic stability of these clones, folate concentrations reported here in four accessions (PI 243510, 472923, 184774, and 205407) were very close to those we previously reported for these same accessions grown under different environmental conditions,20 suggesting that genetically stable clones could be identified. This study shows that systematic screening of indigenous landraces and wild potato species is a valuable approach in order to extend the limits of thiamin and folate concentrations beyond those found in modern cultivars. We identified clones which contained over 2-fold the amount of thiamin and 4-fold the amount of folate in Russet Burbank, a potato variety largely grown in North America. Based on thiamin and folate concentrations found in RN 039.05 (PI 320387) and S. boliviense (PI 597736) (16401 and 3031 ng g 1 DW, respectively), one can estimate that introgression of quantitative trait loci associated with the high thiamin or folate phenotypes into modern potato varieties would give thiamin and folate concentrations of 3280 and 606 ng g 1 FW, respectively, assuming a 20% dry matter content (which is the average dry matter content found in mature tubers of most modern varieties). This means that such cooked high-thiamin potatoes (assuming an 86% retention of thiamin after oven-baking, the most destructive cooking method reported for thiamin13) would provide 56, 38, and 15% of the recommended daily allowance for thiamin (1.2 mg for healthy male adults) in Europe, North America, and Asia, respectively, where per capita consumption of potato in 2005 was 87.8, 60.0, and 23.9 kg, respectively (FAOSTAT). Similarly, such cooked highfolate potatoes (assuming an average 80% retention of folate after cooking21) would provide 28.8, 20.0, and 7.9% of the recommended daily allowance for folate (400 μg for healthy male adults) in Europe, North America, and Asia, respectively. By comparison, a baked russet potato commonly consumed in the U.S. provides 9.2% and 11.0% of the recommended daily allowance of thiamin and folate, respectively, according to the USDA Nutrient Database SR23, based on a 164 g daily consumption (North American average in 2005). Therefore, these clones should be useful in breeding programs aiming to enhance the nutritional value of potato. The development of new potato varieties with increased thiamin and folate concentrations will likely benefit the health status of consumers who do not or cannot follow dietary guidelines. 13078

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Journal of Agricultural and Food Chemistry Future studies should focus on screening more populations within promising species to identify clones with potentially even higher thiamin or folate contents than those reported here. Natural genetic diversity has been successfully used to explore metabolism regulation,22 26 and the materials reported in this paper could be useful tools for such investigations. Unveiling the regulation of these vitamins for which very little is currently understood6 will certainly provide useful information to biofortifying food crops. Also, additional replications will be necessary to determine the genetic stability of these clones, as large differences in thiamin or folate contents between years were sometimes noted. These materials might be great tools for study of, and eventual management of, the environment stimuli that increase thiamin and folate.

’ AUTHOR INFORMATION Corresponding Author

*Phone: 541 567 8321. Fax: 541 567 2240. E-mail: aymeric. [email protected]. Funding Sources

This work was supported by funding from the Agricultural Research Foundation and the Potato Commissions of Oregon, Washington, and Idaho.

’ ACKNOWLEDGMENT The authors would like to thank Dr. John Bamberg from the U.S. Potato Genebank for selecting and providing potato tubers, and Dr. Kathleen Haynes for critical reading of the manuscript. ’ ABBREVIATIONS USED FW, fresh weight; DW, dry weight ’ REFERENCES (1) Christian, P. Impact of the Economic Crisis and Increase in Food Prices on Child Mortality: Exploring Nutritional Pathways. J. Nutr. 2010, 140, 177S–181S. (2) Bouis, H. E. Plant breeding: a new tool for fighting micronutrient malnutrition. J. Nutr. 2002, 132, 491S–494S. (3) Backstrand, J. R. The history and future of food fortification in the United States: a public health perspective. Nutr. Rev. 2002, 60, 15–26. (4) Harper, C. Thiamine (vitamin B1) deficiency and associated brain damage is still common throughout the world and prevention is simple and safe!. Eur. J. Neurol. 2006, 13, 1078–82. (5) Suskind, D. L. Nutritional Deficiencies During Normal Growth. Pediatr. Clin. N. Am. 2009, 56, 1035–1053. (6) Hanson, A. D.; Gregory, J. F. Folate Biosynthesis, Turnover, and Transport in Plants. In Annual Review of Plant Biology; Merchant, S. S., Briggs, W. R., Ort, D., Eds.; Annual Reviews: Palo Alto, 2011; Vol. 62, pp 105 125. (7) Storozhenko, S.; Rabanel, S.; Zhang, G. F.; Rebeille, F.; Lambert, W.; Van Der Straeten, D. Folate enhancement in staple crops by metabolic engineering. Trends Food Sci. Technol. 2005, 16, 271–281. (8) Bailey, L. B.; Rampersaud, G. C.; Kauwell, G. P. Folic acid supplements and fortification affect the risk for neural tube defects, vascular disease and cancer: evolving science. J. Nutr. 2003, 133, 1961S– 1968S. (9) Ramos, M. I.; Allen, L. H.; Mungas, D. M.; Jagust, W. J.; Haan, M. N.; Green, R.; Miller, J. W. Low folate status is associated with impaired cognitive function and dementia in the Sacramento Area Latino Study on Aging. Am. J. Clin. Nutr. 2005, 82, 1346–1352.

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