drought impacts mineral contents in andean potato cultivars

11
DROUGHT STRESS Drought Impacts Mineral Contents in Andean Potato Cultivars I. Lefe ` vre 1 , J. Ziebel 1 , C. Guignard 1 , J.-F. Hausman 1 , R. O. Gutie ´ rrez Rosales 2 , M. Bonierbale 2 , L. Hoffmann 1 , R. Schafleitner 2 & D. Evers 1 1 Centre de Recherche Public – Gabriel Lippmann, Department EVA, Belvaux, Luxembourg 2 International Potato Center, Germplasm Enhancement and Crop Improvement Division, La Molina, Lima, Peru Introduction Potato is the fifth most consumed food crop in the world and is an excellent source of nutrients including carbohy- drates, proteins, vitamin C, several vitamin B and miner- als (Camire et al. 2009, White et al. 2009). Amongst the minerals of nutritional importance are potassium, magne- sium, iron and phosphorus. Relatively high concentra- tions of organic compounds, such as vitamin C present in potato tubers, enhance the absorption of mineral micronutrients by humans (White et al. 2009). Andean landraces cover the largest part of the available genetic diversity of cultivated potato; several authors previously showed that their tuber mineral concentrations were related to genotype (Andre ´ et al. 2007, Burgos et al. 2007) as well as, for a given genotype, to environmental condi- tions (Burgos et al. 2007, Di Giacomo et al. 2007). Pro- duction in areas with low mineral phytoavailability decreases nutrient acquisition by plant tissues (White and Broadley 2009). Consequently, cultivars with an increased ability to acquire mineral elements could be valuable for these non-optimal-cultivation lands. Among the abiotic stresses, drought is one of the major limitations for sustainable agriculture worldwide. Over 35 % of the world’s land surface is considered to be arid or semi-arid, experiencing precipitation that is inadequate for most agricultural uses (Wood 2006). The Intergovern- mental Panel on Climate Change (IPCC 2007) estimates that areas affected by drought have increased since the 1970s. Many already dry regions may experience a decrease Keywords drought; mineral nutrients; Solanum tuberosum; tubers; yield Correspondence D. Evers Centre de Recherche Public – Gabriel Lippmann, Department EVA, 41, rue du Brill, L-4422 Belvaux, Luxembourg Tel.: 00352 47 02 61 441 Fax: 00352 47 02 64 Email: [email protected] Accepted November 23, 2011 doi:10.1111/j.1439-037X.2011.00499.x Abstract Mineral micro- and macronutrients in tubers of 21 Andean potato cultivars were investigated in a field trial under control and drought conditions. Mineral concentrations in potato tubers were highly variable between genotypes; some were significantly and positively correlated with each other, the most notewor- thy associations being Na–Ca, Mn–Mg and Zn–Fe, in both control and drought-stressed plants. Overall, increasing yields are related to decreased con- centrations of some nutrients, albeit some higher-yielding cultivars also dis- played important concentrations of nutrients in their tubers. The most striking result was the increase in the concentration of the majority of the analysed cations in a large number of cultivars in response to water depletion; some of them, such as K, may be related to water homeostasis and/or to sucrose load- ing and unloading in phloem sap. Tuber mineral concentrations were not related to drought tolerance in terms of tuber productivity. Interestingly, yield loss under drought was not correlated with yield potential under control condi- tions. Identification of cultivars such as 703264 and 701106 able to maintain good yield stability in association with high mineral contents under water deprivation is of particular interest, especially in view of the importance of potato as a staple crop and the expansion of its cultivation to non-optimal cul- tivation areas in the context of changing climatic conditions. J. Agronomy & Crop Science (2012) ISSN 0931-2250 196 ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206

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DROUGHT STRESS

Drought Impacts Mineral Contents in Andean PotatoCultivarsI. Lefevre1, J. Ziebel1, C. Guignard1, J.-F. Hausman1, R. O. Gutierrez Rosales2, M. Bonierbale2,L. Hoffmann1, R. Schafleitner2 & D. Evers1

1 Centre de Recherche Public – Gabriel Lippmann, Department EVA, Belvaux, Luxembourg

2 International Potato Center, Germplasm Enhancement and Crop Improvement Division, La Molina, Lima, Peru

Introduction

Potato is the fifth most consumed food crop in the world

and is an excellent source of nutrients including carbohy-

drates, proteins, vitamin C, several vitamin B and miner-

als (Camire et al. 2009, White et al. 2009). Amongst the

minerals of nutritional importance are potassium, magne-

sium, iron and phosphorus. Relatively high concentra-

tions of organic compounds, such as vitamin C present in

potato tubers, enhance the absorption of mineral

micronutrients by humans (White et al. 2009). Andean

landraces cover the largest part of the available genetic

diversity of cultivated potato; several authors previously

showed that their tuber mineral concentrations were

related to genotype (Andre et al. 2007, Burgos et al. 2007)

as well as, for a given genotype, to environmental condi-

tions (Burgos et al. 2007, Di Giacomo et al. 2007). Pro-

duction in areas with low mineral phytoavailability

decreases nutrient acquisition by plant tissues (White and

Broadley 2009). Consequently, cultivars with an increased

ability to acquire mineral elements could be valuable for

these non-optimal-cultivation lands.

Among the abiotic stresses, drought is one of the major

limitations for sustainable agriculture worldwide. Over

35 % of the world’s land surface is considered to be arid

or semi-arid, experiencing precipitation that is inadequate

for most agricultural uses (Wood 2006). The Intergovern-

mental Panel on Climate Change (IPCC 2007) estimates

that areas affected by drought have increased since the

1970s. Many already dry regions may experience a decrease

Keywords

drought; mineral nutrients; Solanum

tuberosum; tubers; yield

Correspondence

D. Evers

Centre de Recherche Public – Gabriel

Lippmann, Department EVA, 41, rue du Brill,

L-4422 Belvaux, Luxembourg

Tel.: 00352 47 02 61 441

Fax: 00352 47 02 64

Email: [email protected]

Accepted November 23, 2011

doi:10.1111/j.1439-037X.2011.00499.x

Abstract

Mineral micro- and macronutrients in tubers of 21 Andean potato cultivars

were investigated in a field trial under control and drought conditions. Mineral

concentrations in potato tubers were highly variable between genotypes; some

were significantly and positively correlated with each other, the most notewor-

thy associations being Na–Ca, Mn–Mg and Zn–Fe, in both control and

drought-stressed plants. Overall, increasing yields are related to decreased con-

centrations of some nutrients, albeit some higher-yielding cultivars also dis-

played important concentrations of nutrients in their tubers. The most striking

result was the increase in the concentration of the majority of the analysed

cations in a large number of cultivars in response to water depletion; some of

them, such as K, may be related to water homeostasis and/or to sucrose load-

ing and unloading in phloem sap. Tuber mineral concentrations were not

related to drought tolerance in terms of tuber productivity. Interestingly, yield

loss under drought was not correlated with yield potential under control condi-

tions. Identification of cultivars such as 703264 and 701106 able to maintain

good yield stability in association with high mineral contents under water

deprivation is of particular interest, especially in view of the importance of

potato as a staple crop and the expansion of its cultivation to non-optimal cul-

tivation areas in the context of changing climatic conditions.

J. Agronomy & Crop Science (2012) ISSN 0931-2250

196 ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206

in precipitation, and heat waves have become more fre-

quent over most agricultural lands, leading to restricted

water availability of variable duration (Wood 2006, IPCC

2007). Soil water is a major limiting condition for yield

and quality of potatoes, as shown by many irrigation

experiments. Thus, potato crop is classified as sensitive to

water stress (McKersie and Leshem 1994, Costa et al. 1997,

Yuan et al. 2003). Reducing water during tuber initiation

severely hinders plant physiological processes and penalizes

tuber yield (Costa et al. 1997). This yield decrease is the

consequence of a significant reduction in tuber number

(Deblonde et al. 1999, Yuan et al. 2003, Eiasu et al. 2007),

but also a consequence of a reduction in tuber size (Schaf-

leitner et al. 2007). Albeit it has been shown that yield loss

under drought may be correlated with the yield potential

under irrigated conditions – highest yielding clones having

the highest yield drop – some clones can present high yield

and good yield stability (Schafleitner et al. 2007).

Drought can affect tuber mineral content by acting on

mineral composition of different tissues and, as a conse-

quence, on the redistribution of minerals within the

plants. Actually, acquisition of many water-soluble nutri-

ents is above all determined by mass flow of soil water

to roots as a result of plant transpiration through the

leaves (Barber 1995). To the best of our knowledge,

the interaction between drought and modulation of

mineral concentrations in potato has not been investi-

gated previously.

Identification of potato cultivars with good yield stabil-

ity and high nutritional quality also in respect to mineral

nutrients under water deprivation would be of great ben-

efit for consumers in some areas where this crop is a die-

tary mainstay. In this respect, the aim of this study was

(i) to investigate the diversity of mineral nutrients in

tubers of a set of field-grown Andean potato cultivars and

(ii) to determine drought impact on the level of these

mineral nutrients in relation to yield loss.

Material and methods

Plant material and culture conditions

Sprouted seed tubers of 21 Andean potato cultivars were

planted on 9 October 2006 in four plots covered by rain

shelters at the International Potato Center (CIP) experi-

mental station Huancayo, Peru, at 3200 m above sea level,

in a randomized complete bloc design with four replicates

of five plants per cultivar. Each rain shelter was equipped

with plastic roofs and plastic barriers 60 cm below

ground to prevent uncontrolled water inflow and with

plastic nets to exclude insects. Plots were filled with

humic soil with pH 4 to a soil depth of 50 cm. They were

fertilized with 100/160/120 kg ha)1 nitrogen–phosphate–

potassium before planting and with 100 kg ha)1 nitrogen

at hilling, 28 days after planting. Soil analysis indicated a

high organic content (between 30.5 % and 38.7 %), and a

very high Cation Exchange Capacity (CEC) (from 51.20

to 54.72 meq 100 g)1) with a base saturation between

71 % and 81 %, situating the soil at a lower limit of satu-

ration. These data indicate a relatively rich soil horizon

with a potentially high microbial activity. Fungicide and

insecticide sprays (mancozeb, propineb, dimetofor, cym-

oxanil, permethrin and cypermethrin) were applied in

weeks 4, 6, 8 and 10 after planting according to suppliers’

recommendations. Plants were watered by drip irrigation,

and soil water potential was kept between 0 and

)0.02 MPa. In the drought plot, irrigation was stopped

on day 86 after planting and drought was applied for

58 days, while the control plot was continuously irrigated.

Soil water content was determined in each replicate plot

and treatment as described by Evers et al. (2010); 37 days

after the onset of drought, soil water content reached val-

ues of around 53 % in the control plot and 32 % in the

drought plot and decreased further to 29 % after 53 days

of water depletion and to 25 % after 58 days of water

depletion, while soil water content remained around

47 % in control plots 58 days after the onset of drought.

After the drought period, irrigation was resumed and

continued until day 156 after planting. On day 163, the

haulms were cut and tuber harvest took place on day 170

after planting. The CIP number, the related variety and

the taxonomic group are used for the description of the

21 potato cultivars of this study (see also Table 2).

Yield analysis

Tubers of the three central plants of a bloc were harvested

170 days after planting. Fresh weight was determined

immediately after harvest. An aliquot of the tubers was

dried in an oven for dry matter determination.

Yield maintenance under drought stress was assessed

by the drought susceptibility index (DSI) calculated

according to the following formula:

DSI = (1)yielddrought/yieldcontrol)/DII. The DII was cal-

culated as (1)Xs/Xi) (Ramırez-Vallejo and Kelly 1998),

where Xs is the mean yield of all cultivars grown under

stress, and Xi is the mean yield of all cultivars grown

under non-stress conditions.

Mineral determination

After thorough washing, whole tubers with skin were

sliced and dried at harvest. Tubers were processed with

their skin owing to the difficulty of uniformly peeling cer-

tain potato tubers with irregular shape. The material was

ground in an IKA A11 stainless steel mill prior to extrac-

Drought Impacts Mineral Contents in Potato Tubers

ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206 197

tion. Samples, 500 mg of dry weight, were digested in

7 ml HNO3 (Plasma Pure 67–70 %; SCP Science, Cour-

taboeuf, France) and 3 ml H2O2 (30 % in weight for

metal traces analysis; Fisher Scientific, Tournai, Belgium).

Acid digestion was performed in Teflon tubes in a micro-

wave oven (Anton Paar Multiwave 3000, Graz, Austria)

by increasing temperature and pressure until 200 �C and

30 bars. At the end of the procedure, samples were

diluted with H2O up to 50 ml and kept at 4 �C prior to

analysis. Blank and certified reference material (white cab-

bage, IAEA-359; LGC Standards, Molsheim, France) were

included at each mineralization cycle for quality control.

Samples were analysed by inductively coupled plasma

mass spectrometry (ICP-MS) (Perkin Elmer Elan DRC-e,

Waltham, MA, USA). For each cultivar, extraction was

performed on three samples, which consisted each of

three pooled tubers from the same plant. Each sample

was extracted in duplicate.

Statistical analyses

The data were analysed by two-way anova, with treatment

and accessions as main effects. Multiple comparison proce-

dure between means was performed with a Tukey test with

confidence limit of 95 % using SigmaStat (Systat Software

Inc., San Jose, CA, USA) for Windows version 2.03 soft-

ware. Principal component analysis (PCA) was performed

on centred and reduced data to compare mineral profiles

and minerals and yield relation with SPSS (v16) (SPSS Inc.

Chicago, IL, USA) and R version 2.8.0 (2008) (http://

www.r-project.org) with FactoMineR package (http://

cran.r-project.org/web/packages/FactoMineR/index.html).

Results

Yield and mineral concentrations upon drought

Susceptibility to drought stress was variable in the investi-

gated set of potato cultivars, as reflected by a wide range

in the DSI (Fig. 1). High DSI corresponds to high

drought susceptibility. Drought caused yield losses

between 39 % (cultivar 703264) and 92 % (cultivar

704022). No correlation existed between this yield loss (in

%) and yield under control conditions among the tested

cultivars (r2 = 9.10)6).

Differences in tuber water content were significant

among control cultivars (P < 0.001) (Fig. 2). Upon

drought, significant changes in tuber water content were

observed in 7 of the 21 cultivars: water content signifi-

cantly increased in tubers from cultivars 701570, 703264,

703312, 703415 and 704022, while it significantly

decreased in those from cultivars 703899 and 706191

under drought condition. No correlation occurred

between tuber water content and yield, neither under

control nor under drought conditions (r2 = 0.007 and

r2 = 0.0021, respectively).

Under control conditions, mineral concentrations

strongly varied between cultivars (Fig. 3). When reported

to an edible portion (150 g FW), micronutrient contents

were between 456.5 and 1199.3, 88.4 and 212.6, 54.9 and

143,7, 334.5 and 1312.5 lg per 150 g FW for Fe, Mn, Cu

and Zn respectively. Macronutrient contents ranged

Fig. 1 Drought susceptibility index (DSI) of potato cultivars. High DSI

indicates high drought susceptibility. DSI is calculated as

DSI = (1)yielddrought/yieldcontrol)/DII. The DII was calculated as (1)Xs/

Xi), where Xs is the mean yield of all cultivars grown under

stress, and Xi is the mean yield of all cultivars grown under non-stress

conditions.

Fig. 2 Water content in tubers of potato cultivars from control and

drought-stressed plants. Values are means ± S.D. For a given cultivar,

*indicates a significant difference (P < 0.05) between control and

drought-stressed plants.

Lefevre et al.

198 ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206

Fig. 3 Concentrations of some minerals in tubers from control and drought-stressed plants. Values are means ± S.D. For a given cultivar, *indi-

cates a significant difference (P < 0.05) between control and drought-stressed plants.

Drought Impacts Mineral Contents in Potato Tubers

ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206 199

between 439.5 and 966.59, 13.18 and 28.08, 5.2 and 18.9,

1.25 and 5.48 mg per 150 g FW, for K, Mg, Ca and Na

respectively. Correlations were found between concentra-

tions of some minerals and yield under control condi-

tions (Table 1); yield was negatively correlated to the

macronutrients Na, K and Ca (P < 0.01) and to the mi-

cronutrients Mn and Zn (P < 0.05). Similarly under

drought, variation was important within the cultivars

(Fig. 3), and yield was negatively correlated to the ma-

cronutrients Na, K (P < 0.01), Mg and Ca (P < 0.05),

and to the micronutrients Mn (P < 0.05) and Zn

(P < 0.01).

Concomitancy of mineral concentration changes upon

drought

The double logarithmic matrix correlation highlighted

many highly positive significant correlations (P < 0.01)

between pairs of measured variables (Table 1), pointing

to a strong relationship between the concentrations of

some minerals in tubers from control or drought-stressed

plants. In control plants, the concentration of the macro-

nutrient K was correlated with all the mineral elements,

Ca and Mg were correlated together and with Na and

Mn, and the micronutrients Zn, Fe and Mn presented

correlations. These correlations tended to increase in

response to drought application, indicating some modifi-

cations in mineral accumulation. The following correla-

tions were noteworthy because of their high correlation

coefficients (r > 0.65) (Table 1) and the similarity in

vector length and direction in PCA plot performed on

variables (Fig. 4a and b) in both control and drought

plants: Na–Ca, Mn–Mg and Zn–Fe. Copper presented a

different trend than the other minerals.

Principal component analysis performed on the vari-

ables DSI and mineral element concentration of the 21

potato cultivars under control (Fig. 4a) and drought con-

ditions (Fig. 4b) showed that the first two principal com-

ponents accounted for 57.08 % and 62.64 %, respectively.

The length of the variable vector indicated that mineral

concentrations were well represented by the PC1 and

PC2, but DSI was not, as confirmed by the Pearson corre-

lation coefficient determined on log-transformed data.

This result indicated that mineral concentrations were not

associated with drought tolerance, in terms of DSI

(Fig. 4a and b).

Plots of variables indicated differences between mineral

concentrations in tubers from control and drought-

stressed plants (Fig. 5). According to a one-way anova

over the whole sample set, drought treatment implicated

significantly higher Cu, Fe, Mg, K and Zn concentrations

in tuber dry matter as compared to control plants, K, Fe,

Cu and Zn presenting variations in the highest number of

cultivars (Fig. 3). Copper was found in higher concentra-

Table 1 Pearson correlation coefficient performed on mineral concentrations indicated in lg g)1 DW and yield. Double logarithmic matrix corre-

lation for all the samples (when P > 0.05, values are not shown in table).

LogNa LogMg LogK LogCa LogFe LogMn LogCu LogZn

Potatoes from control plants

LogYield )0.377** )0.428** )0.344** )0.286* )0.282*

LogNa 0.461** 0.374** 0.730** 0.352**

LogMg 0.506** 0.513** 0.756** 0.256*

LogK 0.412** 0.456** 0.488** 0.345** 0.515**

LogCa 0.438** 0.283*

LogFe 0.382** 0.436** 0.678**

LogMn 0.353**

LogCu 0.370**

LogZn

Potatoes from drought-stressed plants

LogYield )0.345** )0.315* )0.392** )0.276* )0.312* )0.351**

LogNa 0.675** 0.583** 0.834** 0.408** 0.546** 0.414**

LogMg 0.525** 0.674** 0.630** 0.686** 0.412**

LogK 0.646** 0.586** 0.482** 0.688**

LogCa 0.568** 0.634** 0.484**

LogFe 0.491** 0.308* 0.703**

LogMn 0.450**

LogCu 0.437**

LogZn

**Correlation is significant at the 0.01 level; *Correlation is significant at the 0.05 level in grey; correlation >0.500

Lefevre et al.

200 ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206

tion in drought-exposed tubers in nearly all genotypes. In

cultivars 701524, 701570, 702464, 703264, 703356, 703415

and 704647, the concentration of at least four mineral

elements was increased in response to drought stress.

Sodium concentration in tubers from drought-stressed

plants was significantly lower than in control ones,

whereas no significant changes were found for Ca and

Mn. These modifications induced a decrease in Na/K

ratio in all the tuber set, which was significant for six cul-

tivars, 701106, 702568, 703264, 703899, 703988 and

705548 (Table 2). The ratio monovalent/divalent cations

only increased in tubers of two cultivars (Table 2). As can

be seen in Figure 5, mineral concentrations could not be

associated with any particular Solanum tuberosum group,

as they were highly variable within the groups.

Discussion

Variability in mineral micro- and macronutrients in the

investigated set of potato cultivars

Mineral micro- and macronutrient concentrations in

tubers were highly variable (Fig. 3). Overall, the contents

of macroelements are in the range of those reported by

different authors for flesh and skin of raw potatoes. Only

the mean value of K content is slightly higher than usu-

ally reported in literature (Heseker and Heseker 1993,

Souci et al. 2000, U.S. Department of Agriculture 2009).

As for the mineral micronutrients, Fe contents were in

the range of values reported by Souci et al. (2000) but

lower than those reported by the food composition table

of the U.S. Department of Agriculture (2009) (1170 lg

per 150 g FW). Higher levels of Zn were found in this

study compared with the values found in literature, while

Mn and Cu contents were lower (Heseker and Heseker

1993, Souci et al. 2000, U.S. Department of Agriculture

2009). Selenium concentrations remained under the

threshold of detection. Differences in mineral element

contents with values found in literature may depend on

genotypes and environmental factors as already men-

tioned, but also on the potato sampling as reported by

Andre et al. (2007).

Among our set of potatoes, variations in the concentra-

tions of minerals are related to genotypes. Genotypic vari-

ations have previously been reported in Andean potato

varieties for the studied elements Ca, Fe and Zn (Andre

Fig. 4 Principal component analysis between mineral concentrations

indicated in lg g)1 DW and drought susceptibility index (DSI) in

tubers from control (a) and drought-stressed (b) plants.

Fig. 5 Principal component analysis between variables of mineral

concentrations indicated in lg g)1 DW in 21 control and drought-

stressed cultivars. Results from three plants are represented for each.

Drought Impacts Mineral Contents in Potato Tubers

ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206 201

et al. 2007, Burgos et al. 2007) and, according to numer-

ous studies, can be extended to other elements both

between and within Solanum species, as reviewed by

White et al. (2009). In our study, this variability occurred

for all the nutrients analysed. These variations could be

partly explained by the size of potato tubers; skin and

flesh can differ in their amount of certain elements

(Wszelaki et al. 2005, Burgos et al. 2007, Subramanian

et al. 2011), and variation in the ratio flesh/skin dry

weight may be the reason. Andre et al. (2007) explained

about 13 % of the variability in tuber Fe concentrations

by tuber size. However, other authors did not find any

association between tuber size and concentrations of ele-

ments, such as Ca, although its concentration was gener-

ally more important in skin than in flesh (Bamberg et al.

1993). The most important factor in mineral variability is

probably linked to the plant physiology itself, i.e., the

capacity the plant has to absorb and redistribute elements

in its tissues. Numerous factors can interfere, such as

plant development and morphology, which are related to

the cultivar phenotype under varying environments

(Cotes et al. 2002, Kadaja and Tooming 2004), transport

processes in the plant and ion specificity (see for review

Karley and White 2009). Some elements such as K or Mg

are easily translocated within the plant by mass flow,

while some others require chelators to be transported

over a long distance (White et al. 1981a,b). Moreover,

redistribution of some elements to sink organs is low; Ca

is present at low concentration in phloem, and thus, its

movement from leaves to fruits, seeds and tubers is lim-

ited (White and Broadley 2003, Karley and White 2009).

Despite the fact that Ca may move with water to tubers

via small roots growing from the base of the tuber buds

and on the stolon (Kratzke and Palta 1985, 1986), its

concentration remains low in this organ, as evidenced by

our results. These changes in the moving of mineral ele-

ments within the plant are supported by the study of

Subramanian et al. (2011) who observed a pattern of dis-

tribution in the tuber directly related to the importance

of element unloading from the phloem.

Even if cation mobility differs depending on ion speci-

ficity, positive correlation between some elements was

observed in our study; some potato cultivars thus pre-

sented high concentrations of a number of mineral nutri-

ents. A positive correlation between Zn and Fe was

already reported when calculated on a fresh weight basis

(Burgos et al. 2007) or dry weight basis (Rivero et al.

2003). The latter study also reported strong correlations

between Cu and Zn, Fe and Zn, Mg and Zn, Ca and Fe.

Some correlations were not observed in the present study,

Table 2 Ratio of some mineral concentration in potato tubers under control and under drought stress

CIP number Variety Taxonomic group

Na/K ·100 Monovalent/divalent cations

Control Drought Control Drought

700234 SA-2563 Andigena 0.24 ± 0.03 0.15 ± 0.05 24.09 ± 0.85 31.88 ± 6.67*

701106 Camotillo Amarillo Andigena 0.48 ± 0.33 0.14 ± 0.02* 23.93 ± 7.62 29.50 ± 4.61

701524 Puca Huayro 0.31 ± 0.14 0.26 ± 0.05 22.42 ± 3.87 22.88 ± 5.29

701570 Chaucha Phureja 0.60 ± 0.38 0.45 ± 0.16 18.97 ± 0.87 15.92 ± 3.99

702464 Natin Suito 0.43 ± 0.14 0.30 ± 0.04 25.68 ± 5.65 24.16 ± 1.48

702568 Pichea Papa Andigena 0.49 ± 0.23 0.25 ± 0.10* 23.00 ± 4.37 26.49 ± 1.94

703264 Puca Quitish Andigena 0.65 ± 0.30 0.36 ± 0.07* 18.95 ± 4.26 21.91 ± 2.50

703312 Morada Taruna Stenotomum 0.36 ± 0.20 0.22 ± 0.09 25.26 ± 5.35 27.02 ± 3.96

703356 Peruanita Goniocalyx 0.57 ± 0.21 0.43 ± 0.10 21.65 ± 3.37 23.22 ± 5.30

703387 Huamantanga Andigena 0.43 ± 0.22 0.25 ± 0.07 25.36 ± 4.26 32.15 ± 2.06*

703415 Raiz del Palo Andigena 0.32 ± 0.01 0.22 ± 0.09 25.19 ± 0.31 26.70 ± 5.50

703825 China Runtush Goniocalyx 0.59 ± 0.21 0.49 ± 0.06 19.56 ± 1.35 20.94 ± 0.58

703899 Chaucha Roja Andigena 0.51 ± 0.21 0.23 ± 0.06* 21.16 ± 3.63 26.88 ± 1.86

703988 Canchillo Andigena 0.36 ± 0.13 0.17 ± 0.12* 27.03 ± 3.75 31.04 ± 5.30

704022 Kellu Suito Stenotomum 0.41 ± 0.01 0.33 ± 0.02 22.20 ± 3.27 22.02 ± 4.19

704338 Violeta Andigena 0.54 ± 0.17 0.36 ± 0.10 17.00 ± 2.15 21.29 ± 3.95

704647 Unknown Andigena 0.35 ± 0.15 0.20 ± 0.07 18.72 ± 3.36 23.58 ± 1.20

705191 Unknown Andigena 0.26 ± 0.08 0.24 ± 0.01 24.02 ± 1.83 21.70 ± 0.57

705548 Yurac Ccompis Andigena 0.63 ± 0.03 0.24 ± 0.04* 24.22 ± 2.65 28.74 ± 2.61

705940 Larga Stenotomum 0.34 ± 0.10 0.20 ± 0.05 25.03 ± 3.19 27.27 ± 4.01

706191 Cuchi Chucchan Andigena 0.22 ± 0.06 0.20 ± 0.06 26.35 ± 2.28 25.17 ± 2.26

Values are means ± S.D.

*Indicates significant differences between treatments at the a = 0.05 level.

CIP, International Potato Center.

Lefevre et al.

202 ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206

which was performed on different cultivars, in different

soil and climate conditions. Mineral absorption and

retranslocation are partly related to plant architecture and

environmental conditions. Nevertheless, such associations

between minerals are also related to the selectivity of their

transport in plant organs and tissues. In plant plasma

membranes, channels catalysing K+ influx are K+-selective

and voltage-dependent, but some other voltage-indepen-

dent channels were observed in plasma membranes and

vacuolar membrane, and are reported as non-selective

cation channels because of their permeability to not only

other monovalent but also divalent cations (Demidchik

and Maathuis 2007). The uptake of some divalent cations,

such as Ca2+and Mg2+, for which no selective pathways

have been found in plant membranes at resting mem-

brane potentials, is widely considered to be catalysed by

the latter channels (Demidchik and Maathuis 2007).

Some ions such as Zn and Fe can be mediated by identi-

cal groups of transporters (White and Broadley 2009).

In the present investigation on a set of 21 Andean cul-

tivars, a correlation between higher-yielding cultivars and

lower concentration of some nutrients was observed

(Table 1), as was also reported by White et al. (2009).

However, it is not a rule; many interactions between plant

and soil composition, fertilizer application or crop geno-

type are likely to affect concentration of mineral elements

in tubers. Despite being significant, the negative correla-

tion between yield and nutrients found in our study is

not striking (r > )0.5) and higher-yielding cultivars can

contain important concentrations of nutrients. Moreover,

it is not excluded that under other environmental condi-

tions, this correlation disappears.

Drought effect on potato mineral concentrations

Our results show that yield loss (in %) under drought is

not correlated with yield in control conditions in the

studied cultivars. Some high-yielding cultivars can main-

tain tuber formation, which is economically of great

interest. Physiological explanation of this genotypic yield

maintenance still remains unclear. According to Schafleit-

ner et al. (2007), canopy size maintenance is an impor-

tant determinant for yield under drought, while Lahlou

and Ledent (2005) found that the drought tolerance index

might be significantly associated with root depth in the

field, but in stressed conditions only. Indeed, a weak can-

opy size is not necessarily related to a low dry matter

accumulation in tubers, as suggested by Tourneux et al.

(2003). These authors showed that a weak foliage expan-

sion, expressed by a low leaf area index and canopy cover,

could contribute to reduced water loss and a better yield-

ing under water depletion, in comparison with a high

foliage expansion.

Our results indicate an increase in most of the analysed

cations. As results are expressed on a dry weight basis,

this increase is not related to a modification of water con-

tent. Variations were not equivalent for all elements, some

increased such as K, Fe, Zn and Cu, some remained con-

stant such as Ca and Mg, and some decreased such as

Na, indicating that the accumulation of elements was not

only the result of a ‘concentration’ of elements linked to

the yield decrease. Moreover, an absence of correlation

between percentage of increase in the different ions and

yield decrease can exclude at least partly this hypothesis.

Some studies have suggested that some mineral elements

could be involved in osmotic adjustment in some tissues

(Farooq et al. 2009). A higher ratio of monovalent to

divalent cations is known to passively influence the

hydration of cell membranes and macromolecules (Mars-

chner 1995). However, our results did not display signifi-

cant trends concerning this ratio, except for two cultivars,

although they displayed inverse trends for K+ and Na+.

The increase in K+ concentration in response to drought

in our set of potatoes may be related to water homeosta-

sis and turgor regulation as already suggested by some

authors (Shabala and Lew 2002, Maathuis 2009, Zhu et al.

2010). These findings are supported in the potato crop by

the work of Khosravifar et al. (2008), who showed that

increasing K application under water depletion decreased

leaf water potential through osmotic regulation. Several

studies indicate strong relationships between K+ channel

activity and sugar loading into the phloem (Ache et al.

2001, Deeken et al. 2002); a higher supplementation of K,

in a range of adequate supply, is reported to increase

sucrose transport to tubers (Marschner 1995, Allison et al.

2001). Considering the fact that a K+ gradient in the

phloem has been evidenced (Vreugdenhil 1985), a

hypothesis is that a modification in this gradient in con-

ditions of water depletion may sustain redistribution of

sucrose to sink organs despite a lower photoassimilate

production in source organs. Further studies related to

sucrose production in leaves and its translocation in

phloem are needed to investigate this assumption. Some

high-affinity transporters of K+ may be involved in the

increase in this ion concentration (Szczerba et al. 2009),

which could explain the decrease in the Na/K ratio

observed in our study. Moreover, activation of K uptake

in response to low K availability in soil has also been

reported (Karley and White 2009, Szczerba et al. 2009).

As initial root responses to K deprivation, the activity of

K+ transporters in cellular membranes seems regulated by

post-translational regulation.

It is generally assumed that drought impairs mineral

availability in soil by different processes. Low soil mois-

ture reduces the soil diffusion capacity for some elements

(Sardans et al. 2008). However, in our experiment,

Drought Impacts Mineral Contents in Potato Tubers

ª 2012 Blackwell Verlag GmbH, 198 (2012) 196–206 203

despite a strong decrease in soil water content in drought

soil compared to control one, no modification of CEC

between these two different soil conditions was noticed in

soil analyses (51.84 ± 0.91 and 52.96 ± 2.49 meq 100g)1,

in control and drought soils, respectively). Soil enzymes

also play an essential role in the nutrient mineralization

and may correlate well with nutrient availability (Sardans

and Penuelas 2005), especially in soils with high organic

matter content. Drought affects plant growth by hinder-

ing photosynthesis and metabolic activities (Zhu 2002,

Evers et al. 2010) associated with a decrease in transpira-

tion rate and nutrient absorption, as observed in various

species (Hu et al. 2007, Chołuj et al. 2008, Sardans et al.

2008). These modifications are ion- and organ dependent.

However, reports by Mahouachi et al. (2006) as well as

our results show the opposite trend.

Nutritional values

As already reported, potatoes are an excellent source of K

(Camire et al. 2009, White et al. 2009). All the cultivars

presented more than 15 % of its recommended daily

allowance (RDA, 2000 mg of K supplied by 100 g),

according to the Council Directive 90/496/EEC on nutri-

tion labelling, which is the recommended allowance sup-

plied by 100 g. Three cultivars (703356, 703387 and

703825) displayed more than 30 % of the RDA under the

environmental control conditions presented in this study,

and this value increased under drought conditions

(Fig. 3). Considering the fact that some Peruvian popula-

tions can consume between 200 and 800 g of potatoes

per day (Burgos et al. 2007), tubers of some cultivars pro-

vide consistent contents of several other minerals, such as

Mg, Fe, Zn, Cu and Mn. For example, tubers from the

cultivar 703387 contained 9.6 and 14.2 % of the Cu RDA

(1 mg per 100 g) under control and drought conditions,

respectively. Tubers from the cultivar 703825 contained

5.7 % and 5.8 % of the Fe and Zn RDA (14 mg of Fe

and 15 mg of Zn supplied by 100 g), respectively, under

control conditions.

Conclusions

The investigated set of potato clones displayed a strong

variability in mineral concentrations that was not related

to any drought tolerance in terms of tuber productivity.

Despite the fact that correlations exist between higher-

yielding cultivars and lower concentration of some nutri-

ents, some cultivars such as 703264 and 701106 presented

high tuber yield and high mineral contents associated

with a maintain of productivity under drought stress.

Moreover, most of the analysed mineral nutrient contents

increased in response to water depletion, this trend being

not only the result of a ‘concentration’ of elements linked

to a yield decrease; increase in the macroelement K+ may

be related to water homeostasis and/or to sucrose loading

and unloading in phloem sap.

Acknowledgements

The authors would like to thank Laurent Solinhac and

Sylvain Legay for their excellent technical assistance. This

work was financially supported by the Ministry of Finance

(Luxembourg).

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