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Advances in Space Research 50 (2012) 156–165
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Selection and hydroponic growth of potato cultivars for
bioregenerative life support systems
K. Molders a, M. Quinet b, J. Decat a, B. Secco a, E. Dulière c, S. Pieters c,
T. van der Kooij d, S. Lutts b, D. Van Der Straeten a,⇑
b
a
Laboratory of Functional Plant Biology, Department of Physiology, Ghent University, K.L. Ledeganckstraat 35, 9000 Gent, Belgium
Groupe de Recherche en Physiologie végétale, Earth and Life Institute, Université catholique de Louvain, Croix du sud 4-5, bte L7.07.13,
1348 Louvain-la-Neuve, Belgium
c
Institut Paul Lambin, Clos Chapelle-aux-champs 43, 1200 Bruxelles, Belgium
d
HZPC, Edisonweg 5, 8501 XG Joure (P.O. Box 88, 8500 AB Joure), The Netherlands
Received 22 November 2011; received in revised form 13 January 2012; accepted 25 March 2012
Available online 1 April 2012
Abstract
As part of the ESA-funded MELiSSA program, Ghent University and the Université catholique de Louvain investigated the suitability, growth and development of four potato cultivars in hydroponic culture under controlled conditions with the aim to incorporate such
cultivation system in an Environmental Control and Life Support System (ECLSS). Potato plants can fulfill three major functions in an
ECLSS in space missions: (a) fixation of CO2 and production of O2, (b) production of tubers for human nutrition and (c) production of
clean water after condensation of the water vapor released from the plants by transpiration. Four cultivars (Annabelle, Bintje, Desiree
and Innovator) were selected and grown hydroponically in nutrient film technique (NFT) gullies in a growth chamber under controlled
conditions. The plant growth parameters, tuber harvest parameters and results of tuber nutritional analysis of the four cultivars were
compared. The four potato cultivars grew well and all produced tubers. The growth period lasted 127 days for all cultivars except for
Desiree which needed 145 days. Annabelle (1.45 kg/m2) and Bintje (1.355 kg/m2) were the best performing of the four cultivars. They
also produced two times more tubers than Desiree and Innovator. Innovator produced the biggest tubers (20.95 g/tuber) and Desiree
the smallest (7.67 g/tuber). The size of Annabelle and Bintje potatoes were intermediate. Bintje plants produced the highest total biomass
in term of DW. The highest non-edible biomass was produced by Desiree, which showed both the highest shoot and root DW. The manual length and width measurements were also used to predict the total tuber mass. The energy values of the tubers remained in the range
of the 2010 USDA and Souci-Fachmann-Kraut food composition databases. The amount of Ca determined was slightly reduced compared to the USDA value, but close to the Souci-Fachmann-Kraut value. The concentration of Cu, Zn and P were high compared to
both databases.
Clearly, the yields for the four cultivars used in this study can still be significantly increased. Identification of optimal growth conditions (a.o. nutrient solution management, light conditions) will be the subject of further research.
Ó 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.
Keywords: Advanced life support; CELSS; Harvest index; Hydroponics; Potato; Solanum tuberosum
1. Introduction
⇑ Corresponding author. Tel.: +32 9 264 5185; fax: +32 9 264 5333.
E-mail addresses: [email protected] (K. Molders), muriel.quinet
@uclouvain.be (M. Quinet), [email protected] (J. Decat), benjamin.secco
@ugent.be (B. Secco), [email protected] (E. Dulière), [email protected]
(S. Pieters), [email protected] (T. van der Kooij), stanley.lutts@
uclouvain.be (S. Lutts), [email protected] (D. Van Der
Straeten).
Plant cultivation in Environmental Control and Life
Support System (ECLSS) settings designed for space exploration fulfills three major functions: (1) CO2 assimilation
and production of O2, (2) production of high-quality
human nutrition, and (3) supply of cleaned water after
0273-1177/$36.00 Ó 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.asr.2012.03.025
K. Molders et al. / Advances in Space Research 50 (2012) 156–165
condensation of water vapor produced by transpiration
(Wheeler, 2006; Wheeler et al., 2008; Monje et al., 2003).
From an agricultural viewpoint, plant growth, crop
yield and quality are very dependent on the climatic conditions experienced from seedling to harvest. Protected agriculture in greenhouses optimizes plant growth conditions
to a certain extent and permits to shorten growth cycles
and guarantee a stable product quality. For the application
of plant growth and associated food production in sealed
conditions as a subsystem in an ECLSS setting, characterization of crop growth, potable water, oxygen, crop waste
production rates and dynamics, as well as harvested food
nutritional content and plant nutrient and CO2 assimilation rates are a necessity.
The European Space Agency (ESA)-funded MELiSSA
Food Characterization Program (MFC) aims at generating
datasets (combining the above-mentioned aspects) needed
to enable closure of the air, water and nutrient loops of a
closed regenerative life support system (LSS), based on
mass balances within the system. Thus, a hydroponic system under fully controlled and closed environmental conditions wherein (1) successful crop growth and (2) sufficient
yield of these crops can be obtained, will be developed
and tested in the frame of the MFC program.
The requirements for plant growth under controlled,
sealed conditions, with the final goal to provide life support
resources on long-term surface-based space missions, were
analyzed and translated into selection criteria according to
current knowledge. The four selected crops for the MFC1
project are durum wheat, bread wheat, potato and soybean.
This specific publication focuses on potato. The advantages
of potato for cultivation and processing in a hydroponic setting under sealed space conditions are: (1) the availability of
a large variety of cultivars distributed world-wide, each with
its specific characteristics and processing possibilities; (2)
potatoes can be processed quickly without huge energy
demands as compared to other staple crops; (3) potato has
a limited amount of inedible waste which can be easily
degraded; (4) in a hydroponic system, potato can be harvested continuously providing continuous food supplies.
Potato (Solanum tuberosum) is – in terms of human
consumption – the third most important food crop in the
world after rice and wheat. More than a billion people
worldwide eat potato, and global total crop production
exceeds 300 million metric tons (International Potato Center, CIP, http://www.cipotato.org/potato).
A lot of research has been realized on potato field cultures (Struik et al., 1997; Kolbe and Stephan-Beckmann,
1997a, 1997b; Munoz et al., 2005), but unfortunately these
growth conditions are not comparable to the targeted conditions of closed environment culture in substrate-less
hydroponics. Hence, the results from field-culture are not
directly transposable, and a cultivar ranking exercise based
on these field-derived data will not allow crop selection for
efficient hydroponic culture.
A limited number of data on hydroponic culture of
potato under non-sealed conditions have been published
157
(e.g. Monteiro corrêa et al., 2008; Rolot et al., 2002; Rolot
and Seutin, 1999; O’Brien et al., 1998; Cooper, 1979; Cathey
and Campell, 1977). The US National Aeronautics and
Space Administration (NASA) was the first to initiate experiments using hydroponics under sealed conditions. The first
tests were conducted by Ted Tibbits at the Univeristy of
Wisconsin (1982–1994), followed by Raymond Wheeler at
the Kennedy Space Center (1988–today). Tests showed that
plants grew well and formed tubers using the nutrient film
technique (NFT). Moreover, the analyses confirmed the
short day tendencies for tuberisation and revealed that some
cultivars (e.g. Norland, Denali and Russett Burbank) could
tuberise well under continuous high light. The highest tuber
yields from these controlled environment studies reached
19.7 kg FM m2 or 38 g DM day1 (Wheeler, 2006). Harvest indices (tuber DM/total DM) typically ranged from
0.7 to 0.8, indicating that waste (inedible) biomass would
be less than that from many other crops (Wheeler, 2006).
The following reports on an ESA-financed study to
identify and characterize suitable potato cultivars for cultivation in ECLSS settings. Four potato cultivars were
selected and tested in parallel, with two biological replicates, with the aim to obtain a cultivar ranking, to be followed up by an in depth study of the best performing
cultivars in the future.
2. Materials and methods
2.1. Cultivar selection
UGent consulted the company HZPC (www.hzpc.com),
an expert in breeding and selecting potato cultivars in both
field and hydroponic set-ups. HZPC had 67 cultivars readily
available, 20 of which are grown in greenhouse hydroponics
and from which phenotypic observations were available.
Based on data from the literature (‘The European Cultivated Potato Database’ (http://www.europotato.org/
menu.php), both on hydroponic culture and relative field
performance, and on consultancy advice, a pre-selection
of four potato cultivars for bench test experiments was
made.
The following key criteria were considered to be most
important: (1) nutritional quality (high nutritional content
and tuber dry matter, low levels of anti-nutritional compounds), (2) processability (cooking type, starch content,
tuber shape, thickness of the peel), (3) high yield (tuber
induction, tuber fresh and dry weight, tuber shape, tuber
numbers on a per plant basis), (4) disease resistance, (5)
growth habit suited to space constraints (minimal plant
height and stolon length), (6) maximum harvest index, (7)
minimal root growth and (8) short growth cycle (growing
period, dormancy characteristics).
Four cultivars presenting different phenotypes and endusage characteristics, and known to perform well in greenhouse-based hydroponics were selected: Bintje, Desiree,
Annabelle and Innovator. Table 1 gives a summary of a
few of their main characteristics.
158
K. Molders et al. / Advances in Space Research 50 (2012) 156–165
Table 1
Key parameters of the selected potato cultivars.
Cultivar
Tuber FW yieldb
Tuber DW yield (field culture)a
Tuber sizea
Plant heighta
Maturitya
Annabelle
Bintje
Desiree
Innovator
Very high
Medium
Very high
Medium
Low 18.4%
Medium to high
High 21.40%
High 21.30%
Small
Medium to large
Large
Large
Medium to high
Medium
Medium
Medium to low
Very early
Early to intermediate
Intermediate to late
Early to intermediate
a
b
Information retrieved from ‘The European Cultivated Potato Database’, <http://www.europotato.org/menu.php?>.
Information obtained from HZPC.
2.2. Plant materials and growth conditions
The hydroponic system for potato cultivation was positioned in a walk-in chamber with precise environmental
control. The plant growing area consisted of four 0.5 m
wide and 1.70 m long shelves (Fig. 1) providing a total area
of 3.4 m2. Four dimmable units of eight fluorescent lamps
(Master TL-D reflex Super 80 58W/840 from Philips) illuminated the shelves. Plants were grown in a photoperiod of
16 h day and 8 h night and at an average light intensity of
300 lmol m2 s1 at canopy level. The temperature was
20 °C and the relative humidity 70%. Air temperature
and humidity were controlled by a Siemens RMU730
PLC. The O2 and CO2 concentration were ambient and
measured with a PP Systems electro-chemical cell every
10 min (OP-1 Probe) and a WMA-4 Infrared Gas Analyzer
(IRGA) respectively.
Plants were grown in a thin nutrient solution layer
(nutrient film technique, NFT) in polyurethane coated
stainless gullies (JBHydroponics, Maasdijk, NL) of
170 cm long, 16 cm wide at the bottom (25 cm at the top)
and 9.5 cm high. The gullies were positioned with a downward angle of 5% to allow gravitational drain. Sixteen
plants were placed in each gully with a distance of 10 cm
in between. The gullies were covered with black polyethylene plastic covers to minimize light penetration in the gully
in order to prevent tuber greening. Each gully had a separate nutrient solution circuit and the nutrient flow was
adjusted to 2 L/min. EC, pH, and nutritive solution level
in the circuits were registered by sensors and automatically
readjusted at respectively 1800 lS/cm, 5.5 and 15 L with
three stock solution tanks (pH control with H3PO4/
KOH, EC control with K2SO4 and KH2PO4,). Tank level
was adjusted with distilled water.
The nutrient solution temperature was kept constant at
20 °C with a cooling system (TECO TR5 160W). The nutrient solution composition is described in Table 2. Sampling
of hydroponics solution was performed at the beginning
and end of each nutrient solution change.
For the start-up of the experiment a developmentally
homogenous set of in vitro plantlets was used, produced
by HZPC. The 21 days of in vitro growth at HZPC were
followed by 7 days of in vitro acclimatization in the
propagation room at low light level (50 lmol/m2 s).
Afterwards the in vitro boxes were uncovered to allow
further elongation growth. The plants reached the desired
stem length (min. 10 cm, in order to allow root/nutrient
solution contact) in a few days and were transferred into
the gullies.
After four weeks of growth in the medium, the nutrient
solution was replaced by a solution without nitrogen
source (tuberisation solution) to hasten onset of tuberisation (O’Brien et al., 1998; Goins et al., 2004; Wheeler,
2006; Rolot and Seutin, 1999).
Upon appearance of the first tubers, 2 ml of
Ca(NO3)4H2O (0.9 M) was added daily in order to maintain a low but sufficient level of nitrate in the nutrient solution. Nitrogen content was monitored with test strips
Ò
(NO
3 : Merck Microquant (MiQ)).
At harvest, a peel hardening protocol was executed to
improve tuber conservation. The harvested dry-blotted
tubers were placed in a nearly closed box in the dark at
20 °C for 2 days. The lid of the box was then opened stepwise to allow slow drying of the tubers. Five to seven days
were sufficient to allow the potato lenticels to close. The
tubers were then conserved at 4 °C in the dark.
2.3. Growth and yield measurements
The shoot size, number of leaves, number of stolons and
tubers were recorded every week. Plants were harvested
after 127–145 days, depending on the cultivar. For each
plant, roots, shoots, tubers and stolons were separated
and weighed. Tuber length and width were also measured.
Samples were dried at 70 °C for 72 h and weighed again to
measure the dry weight.
A Cartesian XYZ robot with a rotating arm was used to
image plantgrowth and measure leaf area and leaf temperature in a non-destructive way at regular intervals. The
robot was carrying a thermal infrared camera ThermoVisionÒ A10 (160 120 pixels) to visualize transpiration
and a BCi5 CMOS color camera to capture high resolution
color images (1280 1024 pixels) to follow up growth. The
firewire (IEEE1394) output of the thermal camera and the
USB2 output of the color camera were captured by a Labview application upon positioning of the cameras above the
target plant. The software provides a module to compensate for the difference in alignment and field of view of
the cameras, in order to obtain a perfect match between
the different images sequences upon data analysis.
K. Molders et al. / Advances in Space Research 50 (2012) 156–165
159
Fig. 1. Schematic representation of the hydroponic system: Top view, front view and side view.
Table 2
Nutrient solution composition per element.
Product
Molar
mass
Concentration
(mM)
Concentration
(mg/L)
Macronutrients: vegetative phase
K2SO4
174.25
KH2PO4
136.08
246.48
MgSO47H2O
Ca(NO3)24H2O
236.15
Fer-chelaat
367.1
2.51
1.10
2.08
2.25
0.05
437.50
150.00
511.80
530.62
18.75
Macronutrients: tuberisation phase
174.25
K2SO4
KH2PO4
136.08
246.48
MgSO47H2O
Fer-chelaat
367.10
0.79
4.96
1.56
0.05
137.50
675.00
383.85
18.75
Micronutrients
MnSO4H2O
CuSO45H2O
ZnSO47H2O
EDTA2H2ONa2
Na2MoO4
H3BO3
KCl
0.005
0.005
0.001
0.011
0.0005
0.02
0.01
169.01
249.68
287.5
372.24
249.98
61.83
74.60
0.84
1.25
0.29
4.09
0.12
1.24
0.74
2.4. Nutritional analysis
Nutritional analysis was carried out at the Institute Paul
Lambin (IPL). The following measurements were performed on samples of each of the harvested cultivars: dry
weight (Four samples were weighed (FW); two of them
were placed in a 100 °C oven at atmospheric pressure
(AOAC 984.25), the other two were dried under vacuum
at 50 °C and <50 mbar (AOAC 920.151A). The four samples were weighed again after >15 h drying (DW). All four
samples were treated in parallel. Different protocols are
needed to allow further use of the same samples for other
analysis and is also a verification procedure to rule out
the occurrence of sugar dehydration); Protein content
(Kjeldahl method; N 6.25; AOAC 2001.11); Fat content
(Weibuhl method; acid digestion followed by Soxhlet
extraction with petroleum ether 40–60; International Organization for Standardisation ISO1443:1973); Total Dietary
Fiber (TDF) content (AOAC 985.29 (AOAC, 2005), Enzymatic–Gravimetric Method); mineral content (24 h, 550 °C
furnace; AOAC 923.03); sodium and potassium content
(flame photometry of the mineral solution; AOAC
969.23); calcium, magnesium, iron, zinc, copper and manganese content (atomic absorption of the mineral solution;
AOAC 985.35); Phosphorus content (colorimetry of the
phosphomolybdate complex on an aliquot taken from
Kjeldahl mineralization; International Standard 33A from
the International Dairy Federation 1971)); Available carbohydrates (by difference between total of sample and
sum of other ingredients; AOAC 986.25); Glycoalkaloids
(solanine, chaconine) content (AOAC 997.13, Solid Phase
Extraction (SPE) concentration of the acetic acid extract
followed by HPLC, 202 nm UV detection) and Energy
160
K. Molders et al. / Advances in Space Research 50 (2012) 156–165
content (calculation: 4 kcal for proteins and carbohydrates,
9 kcal for fat, 2 kcal for Total Dietary Fiber. Value is multiplied by 4.184 for kJ. Dir 2003/120/CE Official Journal
L333/51 2003).
The results obtained were compared to existing references, being the USDA and Souci-Fachmann-Kraut food
composition databases. We need to mention however that
energy content was calculated in different ways for IPL,
USDA and Souci-Fachmann-Kraut databases. USDA uses
the Atwater system (http://www.ars.usda.gov/ba/bhnrc/
ndl, Merrill and Watt, 1973), Souci-Fachmann-Kraut uses
the 4–9–4 rule which is a simplified version of the Atwater
system. Neither of these databases adds the 2 kcal/g for
TDF as IPL does and is now recommended by European
Union regulations. E.g. with a ‘4–9–4–2’ rule, energy would
be 83 kcal for USDA and 72 kcal for Souci, so roughly
10% higher.
3. Results and discussion
3.1. Plant growth
The four potato cultivars grew well and all produced
tubers (Fig. 2a–h). The growth period lasted 127 days for
all cultivars except for Desiree which needed 145 days.
Annabelle and Bintje were the first to initiate stolons and
tubers. Stolon initiation occurred respectively 14.9 ± 1.3
and 20.4 ± 2.6 days after transfer of in vitro plants into
the gullies, while tuber initiation was observed after respectively 39 ± 0.8 and 53.4 ± 1.9 days. Desiree initiated stolons after 30.8 ± 1.3 days and was the last to initiate
tubers, which appeared after 84.2 ± 3.3 days, while Innovator initiated stolons after 32.1 ± 3.7 and tubers after
64.1 ± 3.3 days. Annabelle had a shorter life cycle as compared to the other cultivars. All Annabelle plants died
shortly after tuber maturity during the last month of the
experiment, while only one plant died for Bintje and Innovator in the last week, and all Desiree plants survived. To
avoid tuber rot, Annabelle tubers were harvested before
the end of the experiment.
By restricting the amount of N in the nutrient solution,
the average length of the main stem was kept rather low
but homogeneous for the four cultivars, around 35–
40 cm. This was done deliberately, to comply with space
restrictions during a mission scenario. Annabelle was
slightly higher and Innovator slightly smaller than the others plants.
The plant stature was variety dependent. Desiree and
Innovator were more ramified and developed more leaves.
The leaf size of Desiree was significantly reduced compared
to the other cultivars. Bintje and Desiree flowered at the
end of the experiment.
At the UGent site, the independent NFT gully system
with the Annabelle cultivar provided an online weight measurement through load cells supporting the gully. A total
biomass increase of 1900 g was recorded. Adjustment of
gully inclination and nutrient solution flow rate lead to
immediate weight changes of maximum 600 g, due to a
change of the amount of liquid present in the gully.
3.2. Harvest parameters
Annabelle (1.174 kg of total tuber FW for 0.85 m2 of
growth surface) and Bintje (1.085 kg of total tuber FW
for 0.85 m2 of growth surface) were the best performing
of the four cultivars and thus at the top of the ranking
(Table 3). They also produced two times more tubers than
Desiree and Innovator (Table 3). Tubers of Annabelle kept
on growing till plant death, allowing an acceptable harvest
for this early cultivar. The precocity of this cultivar also
explained the rapid senescence of the Annabelle plants.
On the other hand, besides the considerable first harvest
after 3 months of growth, Bintje was able to produce a second and equal harvest only 2 months later. The yield of
Desiree was low due to late and inefficient tuber initiation.
Innovator produced the biggest tubers (20.95 g/tuber)
and Desiree the smallest (7.67 g/tuber). The size of Annabelle and Bintje potatoes were intermediate with respectively 9.68 g and 10.81 g per tuber. Tuber shape
corresponded to respective typical appearance for each cultivar, although fluctuation of N availability often induced
“ginger root shapes” for Innovator and Bintje, and secondary growth of stolons on tubers of Bintje and Desiree (Figs.
2 and 3). Tuber length, width and weight were measured
(Figs. 4–6). The figures show that Annabelle and Bintje
produced many, but smaller tubers, whereas Innovator
produced less, but large tubers. Tuber size and shape are
important parameters with respect to the processability of
the tubers. On a per plant basis, the number of tubers produced by the different cultivars were 10.8 for Annabelle,
9.25 for Bintje, 6 for Desiree and 10.5 for Innovator.
Manual length and width measurements of tubers during
the experiment revealed a constant and regular tuber size
increase from tuber initiation till harvest. At UGent these
manual length and width measurements were also used to
predict the total tuber mass produced. Ideally, 2D pictures
of the gullies from which individual potato length and width
can be measured, could be used to predict the harvest,
which could be valuable for space missions. The calculation
of predicted tuber weight was based on the mathematical
formula to calculate the volume of an ellipsoid.
Tuber volume ¼ ð4=3 pÞ ðtuber length=2Þ
ðtuber width=2Þ2
Estimated tuber mass in g ¼ tuber volume
density ðcultivar dependentÞ
Densities were measured for each cultivar (1.19, 1.20,
1.10 and 1.15 g/cm3 for respectively Annabelle, Bintje,
Innovator and Desiree). The estimated masses for Annabelle, Bintje, Desiree and Innovator were respectively 7%,
12%, 17% and 4% over estimated. These numbers prove
K. Molders et al. / Advances in Space Research 50 (2012) 156–165
161
A
B
C
D
E
F
G
H
Fig. 2. Pictures of plants and tubers of the four cultivars, taken at the end of the growth cycle.
Table 3
Potato harvest results (total cultivation area = 0.85 m2 per cultivar).
Parameter/cultivar
Annabelle
Bintje
Desiree
Innovator
Total number of tubers
Number of tubers per plant
Tuber harvest (kg)
Tuber harvest (g/m2)
Tuber harvest (g/plant)
Total productivity (g/m2/d)
Average FW per tuber (g)
123
10.8
1.174
1450
75
11.18
9.68
101
9.25
1.085
1355
67.8
10.54
10.81
56
6
0.433
545
27.1
3.995
7.67
36
10.5
0.766
940
49.7
7.305
20.95
162
K. Molders et al. / Advances in Space Research 50 (2012) 156–165
A
B
C
D
Fig. 3. Close-up pictures of representative tubers of each cultivar.
Fig. 4. Distribution of tubers according to their length.
Fig. 5. Distribution of tubers according to their width.
that some fine-tuning of this yield prediction technique
(based on real time images) could actually provide a good
estimation of the total tuber mass produced at a certain
time point during tuber growth. Based on the estimated
total tuber mass, a decision could be made on whether or
not to harvest the tubers.
Bintje plants produced the highest total biomass in term
of DW. The highest non-edible biomass was produced by
Desiree, which showed both the highest shoot and root
DW (Table 4). The ratio edible dry weight/total plant dry
weight (harvest index) was more than two times less for
Desiree compared to the others cultivars.
To the best of our knowledge, there are no publications
reporting similar experiments (hydroponics in a controlled
environment system) on the four potato cultivars we used.
The highest yields obtained in these experiments (1.45 kg/
m2 tuber FW) are still low compared to the highest yield
obtained by Raymond Wheeler (19.7 kg/m2 tuber FW)
(Wheeler, 2006). Thus, it is clear that the yields for the four
cultivars in our study can still be significantly increased.
Identification of optimal growth conditions (nutrient
solution management, light conditions, . . .) which positively influence our selection criteria (e.g. yield) is therefore
of key importance.
K. Molders et al. / Advances in Space Research 50 (2012) 156–165
163
Fig. 6. Distribution of the tubers according to their weight.
Table 4
Potato harvest index (total cultivation area = 0.85 m2 per cultivar).
Parameter/Cultivar
Annabelle
Bintje
Desiree
Innovator
Tuber FW (g/plant)
Shoot FW (g/plant)
Root + stolon FW (g/plant)
Tuber DW (g/plant)
Shoot DW (g/plant)
Root + stolon DW (g/plant)
Harvest index (based on DW)
75
27.7
3.42
13.42
3.23
0.49
78.4
67.8
47.57
5.52
15.56
4.79
0.55
74.24
27.1
49.02
20.11
4.21
7.27
1.67
31.82
49.7
77.79
2.31
11.83
4.74
0.3
70.64
Given the particularities of potato culture, especially
with respect to the induction and monitoring of the tuberisation process, it can be stated that N-supply plays a very
important role (Goins et al., 2004; Cao and Tibbits, 1993,
1998). The amount, frequency and forms of N added to the
nutrient solution has a direct effect on the stature and
height of the plant. On the other hand, N reduction may
hasten tuber initiation and tuber growth is stimulated
under certain N limiting conditions (O’Brien et al., 1998;
Goins et al., 2004; Wheeler, 2006). In the post-tuberisation
phase Ca(NO3)2 was added daily in order to maintain a
low level of nitrate in the nutrient solution, as N monitoring showed that NO3 is rapidly taken up by the plants after
being added to the nutrient solution. On the other hand, a
too high availability of nitrate, or N fluctuation induces
stolon growth and stops tuber bulking (Goins et al.,
2004), while a complete depletion of N provokes peel hardening resulting in cracking once nitrate becomes available.
Phosphate supply and the N/P balance also seems to
play an important role in the tuberisation process and the
size of the produced tubers. Phosphate levels should be
low before, and high (high P/N ratio) during tuberisation
(Rolot and Seutin, 1999).
From the above discussion, it is clear that a nutrient
delivery strategy for optimal tuber development will need
to be developed.
3.3. Nutritional analysis
Potatoes will need to cover the high requirements for the
carbohydrate content of the astronaut’s diet, which is their
main nutritional interest. Data of the nutritional analysis
of tubers are presented in Table 5. Desiree potatoes showed
the highest water content. The energy values of the tubers
in our experiments are lower as compared to the USDA
references, due to small differences between cultivars for
the protein, fat, carbohydrate and TDF content. However,
the values obtained for hydroponically grown tubers in this
paper remained in the range of the 2010 USDA and SouciFachmann-Kraut food composition databases. Note that
once normalized for dry weight, energy values of all tubers
are within 10% of 342 kcal/100 g DW, which is the average
between the Souci and USDA data (all energy values recalculated following the same basis of 4 kcal for proteins and
available carbohydrates, 9 kcal for lipids, 2 kcal for TDF).
The amount of Ca determined was slightly reduced compared to the USDA value, but close to the Souci-Fachmann-Kraut value. The concentration of Cu varies
among cultivars, but are very high compared to the
Souci-Fachmann-Kraut and USDA databases. Zn and P
were also increased in our tubers compared to the SouciFachmann-Kraut and USDA databases. These high values
could be caused by the presence of these elements in the
nutrient solution composition. Although, at this moment,
potatoes are not considered as a source to complete the
nutritional requirements for minerals, this needs further
investigation in the future. If we can confirm that the mineral content of the tubers is linked to the composition of
the nutrient solution, this could be a tool to add useful
nutrients to the astronaut’s diet.
Since glycoalkaloids are important anti-nutritional factors, the concentration of the two main potato glycoalkaloids (solanine and chaconine) was analyzed. As presented
in Table 5, neither of those glycoalkaloids were detected.
Total glycoalcaloid content (TGA) is set at maximum
0.2 mg/gFW for commercial potato varieties (Friedman,
2006). Light exposed potatoes can reach alkaloid levels over
1 mg/gFW, which represent a health hazard.
Greening is an indication of solanine buildup, although
solanine can be produced without being linked to greening
(e.g. as a result of mechanical damage). From the pre-selected
cultivars, Annabelle is most and Innovator least resistant to
greening under the influence of (low levels) of light.
164
K. Molders et al. / Advances in Space Research 50 (2012) 156–165
Table 5
Potato tubers nutritional analysis for 100 g of edible mass.
Per
Water (%)
Protein (%) (N 6.25)
Fat (%)
Avail. carbohydrates (%)
TDF (%)
Minerals (%)
(mg/100 g)
(mg/100 g)
(mg/100 g)
(mg/100 g)
(mg/100 g)
(mg/100 g)
(mg/100 g)
(mg/100 g)
N (%)
Crop specific compounds
Solanine (mg/kg)
Chaconine (mg/kg) E
TGA (mg/kg)
Energy (kcal for 100 g)
Energy (kJ for 100 g)
a
b
K
Ca
Mg
Fe
Cu
Zn
Mn
P
Database USDAa
potato (flesh and skin,
(N° 11352)
Database
Souci-Fachmann-Krautb
potato
Annabelle
Bintje
Desirée
Innovator
100 g
79.34
2.02
0.09
17.47
2.20
1.08
421
12
23
0.78
0.108
0.29
0.153
57
0.32
100 g
77.8
2.04
0.11
14.80
2.07
1.02
417
6.2
21
0.42
0.089
0.345
0.147
50
0.33
100 g
79.50 ± 2.19
1.505 ± 0.14
0.05 ± 0.01
14.87 ± 0.90
1.50 ± 0.05
1.02 ± 0.16
434.50 ± 82
5.85 ± 0.44
27.15 ± 2.82
0.65 ± 0.10
0.70 ± 0.49
0.80 ± 0.40
0.20 ± 0.03
93.50 ± 17
0.24 ± 0.02
100 g
77.50 ± 3.92
1.68 ± 0.55
0.04 ± 0.01
16.27 ± 2.64
1.88 ± 0.11
1.23 ± 0.05
501 ± 23
10 ± 3.14
24.10 ± 2.36
0.75 ± 0.05
0.5 ± 0.12
0.75 ± 0.21
0.19 ± 0.09
98.50 ± 13
0.27 ± 0.09
100 g
84.45 ± 0.743
1.52 ± 0.08
0.08 ± 0.01
10.81 ± 0.03
2.01 ± 0.27
1.10 ± 0.04
473.50 ± 5
6.15 ± 1.72
21.40 ± 1.44
0.45 ± 0.07
0.50 ± 0.23
0.70 ± 0.32
0.18 ± 0.05
142 ± 6.9
0.24±0.01
100 g
77.35 ± 2.38
1.67 ± 0.33
0.06 ± 0.02
16.04 ± 2.67
2.00 ± 0.29
1.08 ± 0.02
443.50 ± 27
8.30 ± 0.71
26.15 ± 0.74
0.60 ± 0.12
0.60 ± 0.31
1.20 ± 0.83
0.18 ± 0.05
169 ± 6.1
0.27 ± 0.05
70
293
0
0
–
64.70 ± 3
270.60 ± 12
0
0
–
69.60±13
291.15 ± 56
0
0
–
54.10 ± 1
226.25 ± 3
0
0
–
75.35 ± 13
315.30 ± 54
NA
NA
NA
77
321
US Department of Agriculture, Agricultural Research Service (2010).
Souci-Fachmann-Kraut from the Souci-Fachmann-Kraut Online-Database (2010).
The level of TGA is the major criterion for safe human
consumption; therefore further thorough research will need
to be done on the influence of growth conditions on TGA
levels in potato.
Funding was provided by the European Space Agency
through the MELiSSA project and Ghent University.
References
4. Conclusion
First experiments have shown that potato cultivation
in hydroponic settings with space conditions related to
space mission conditions is feasible but needs further
research in order to optimize nutrient solution composition and developmental stage dependent adaptation
thereof.
Moreover, nutritional analysis proves that the tubers
grown in hydroponic culture have a nutritive quality which
is comparable to that of field-grown tubers. For some mineral elements, the hydroponically grown tubers proved to
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The best yield performance was obtained by Annabelle
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beneficial in terms of dietary requirements and versatility in
processing and menu options.
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This publication is dedicated to the memory of Claude
Chipaux (1935–2010), father of the MELiSSA project.
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