POTATO (SOLANUM TUBEROSUM) MINITUBER PRODUCTION USING
AEROPONICS: ANOTHER ARROW IN THE QUIVER?
Lung’aho C., M. Nyongesa, M.W. Mbiyu, N.M. Ng’ang’a, D.N. Kipkoech, P. Pwaipwai,
and J. Karinga
Kenya Agricultural Research Institute-Tigoni, P.O. Box 338-00217 Limuru, Kenya
Potato is the second most important staple food after maize in Kenya. Limited accessibility to high quality
potato seed is a perennial problem amongst many growers and is partly attributable to inefficiencies in various
stages in the seed production system. The objective of this paper is to review and assess the various options
available for basic seed tuber production and suggest the way forward with particular emphasis on the
applicability of aeroponics technology for minituber production in Kenya. Tissue culture derived greenhouse
and screenhouse grown minitubers are the standard method used in modern limited generation seed potato
programs. Aeroponics would appear to have a number of potential attributes to make seed potato production
more efficient. The technique has potential to eliminate all but one generation of seed potato multiplication in
the field, thus lowering costs and raising the plant health quality of the first field production generation.
Important considerations that should be addressed to ensure an efficiently functioning system are highlighted in
this paper. Possible areas of research to improve productivity include optimizing nutrient solutions, plant
density, number of harvests and harvesting intervals.
Key words: Aeroponics, clonal multiplication, hydroponics, minituber production, rapid multiplication
techniques, tissue culture
The potato is one of the most important food crop in Kenya. It is cultivated in high altitude areas between 1,500
and 3,000 metres above sea level. The major production areas are found in Rift Valley, Central and Eastern
provinces (MOA, 2008). The crop is mainly grown by small scale farmers who account for over 90% of the
production. Most of the production is mainly rainfed and carried out in scattered patches of intensive small-scale
agriculture (McArthur Crissman, 1989; Anonymous, 2009).
Timely availability of high quality planting material of suitable potato varieties is considered to be one of the
most limiting constraints of this crop in Kenya (Crissman et al., 1993). Currently, only 1-2% of the seed potato
demand is being met. An inefficient seed system is a bottleneck to further growth of the potato industry and
negatively impacts on the potato value chain. In the absence of continuous sources of good quality seed many
growers opt to use their own farm saved seed or those obtained from markets. Such practices contribute towards
sub-optimal yields as well as spread of diseases such as bacterial wilt (Ralstonia solanacearum), a serious
disease of potatoes, and viruses (Kaguongo et al., 2008). Properly functioning seed systems generally start with
healthy planting material which is multiplied several times with low rates of degeneration and at an affordable
price. The aim of a multiplication system for seed production should be to produce or maintain a stock of
nuclear seed and multiply this stock as rapidly as is economically feasible, and to feed the system of commercial
seed production with healthy material at a rate that is in accordance with the existing rate of seed degeneration
(Struik and Wiersema, 1999). The trend in seed potato production systems is to minimize the number of field
multiplications because of the inefficiency (and thus high costs) and continuous risk of diseases (mainly, viral,
bacterial and fungal) and pests (such as nematodes) associated with many field multiplications. The objective of
this paper is to review and assess the various options available for basic seed tuber production and suggests the
way forward with particular emphasis on the applicability of the aeroponics technology for minituber production
Materials and Methods
Data on potato production was obtained from the FAO data base (FAOSTAT, 2010). Additional information
was obtained from secondary literature sources including annual reports, journal papers, seed reports and
specialized documents dealing with seed potato production. Seed potato requirements were computed using the
(i) Total seed requirement (tonnes) = Area under potatoes (ha) x planting rate (t/ha)
(ii) Effective seed demand (tonnes) = Proportion of farmers likely to purchase seed x rate of seed renewal
(iii) Quantity of pre-basic seed required to sustain the effective seed demand (tonnes) = Effective seed
demand x 0.6 x 0.1 x 0.1, where 0.6 is the average multiplication factor during the first multiplication
factor of minitubers and 0.1 is the average multiplication factor for subsequent field multiplications
based on experiences at KARI-Tigoni.
(iv) Number of minitubers = Quantity of minitubers required/average weight of one minituber (assumed to
be 10 g).
Results and Discussion
Area under potato and current seed potato requirements
In Kenya, the area under potato has expanded from 87,846 ha in 1990 to 120,000 ha in 2008 (Table 1). At a
planting rate of 2 t ha-1, the total annual certified seed requirement is estimated to have risen from 175,692 in
1990 to 240,000 t in 2008. The effective seed potato demand is much less than this because of two major
factors. First, according to previous work no more than 30% of the farmers purchase improved seed including
potato seed (Venkatesan, 1994) and secondly, because of seed degeneration, the gradual fall in yields due to
accumulation of diseases, farmers are generally advised to renew their seed stocks after 4 seasons of planting i.e.
once in every two years. Thus, the effective potato seed demand was estimated to be 36,000 t of certified seed
per year in 2008 (i.e. 240,000 t x 0.30 x ½). The quantity of pre-basic seed required to sustain the effective seed
demand is approximately 60.0 t. The major assumptions taken in calculating the basic seed requirement are that
there will be three field multiplications at a multiplication rate of 1:6 for the first field multiplication and 1:10
for the second and third field multiplications. Based on the assumption that one minituber weighs 10 g then 60.0
t of pre-basic seed are equivalent to 6.0 million minitubers.
Table 1: Seed potato requirements derived from area under potatoes
Year Area Total seed Effective Quantity of pre-basic No. of minitubers
(ha) requirement seed required to sustain required to sustain
(tonnes) demand effective seed demand the pre-basic seed
(tonnes) (tonnes) requirement
1990 87,846 175,692 26,354 43.9 4,390,000
1991 87,110 174,220 26,133 43.6 4,360,000
1992 68,018 136,036 20,405 34.0 3,400,000
1993 55,670 111,340 16,701 27.8 2,780,000
1994 83,007 166,014 24,902 41.5 4,150,000
1995 96,143 192,286 28,843 48.1 4,810,000
1996 98,024 196,048 29,407 49.0 4,900,000
1997 118,638 237,276 35,591 59.3 5,930,000
1998 90,391 180,782 27,117 45.2 4,520,000
1999 114,614 229,228 34,384 57.3 5,730,000
2000 108,463 216,926 32,539 54.2 5,420,000
2001 121,490 242,980 36,447 60.7 6,070,000
2002 111,747 223,494 33,524 55.9 5,590,000
2003 126,529 253,058 37,959 63.3 6,330,000
2004 128,485 256,970 38,546 64.2 6,420,000
2005 120,859 241,718 36,258 60.4 6,040,000
2006 116,348 232,696 34,904 58.2 5,820,000
2007 120,000 240,000 36,000 60.0 6,000,000
2008 120,000 240,000 36,000 60.0 6,000,000
2009* 153,114 30,6228 45,934 76.6 7,660,000
Table 2: Comparison of different methods of pre-basic seed production
Minituber production method
Characteristic Conventional Conventional
stem cuttings tissue culture
Mutliplication rate 1:6-10 1:3-5 1:6-10 1:50-100
Risk of disease infection Low Modest Modest High
and contamination of an
entire production unit
Labour required High Modest Modest Modest
Land requirement High Medium Medium Low
Cost investment Relatively low Modest Modest investment is
Not required Required Required Not required
(Sterilization of substrate)
Ease of harvesting Not that easy Easy Easy Relatively easy
Potential for using
Rhizobial inoculation to ? ? ? High
Possibility of increasing period can be
Nil Nil Nil
the vegetative period longer by 2-3
Possible but Possible but not
Sequential harvests Not possible Possible
not convenient convenient
Level of management
Average High High Very high
Possibility for tuber size
Minimal Moderate Moderate High
No sterilization Substrate Substrate No sterilization
of substrate sterilization sterilization of substrate
required required required required
Water requirements High Modest Modest low
Nutrient recirculation Nor possible Nor possible Nor possible Possible
Potential for reducing the
number of field Nil Medium Medium High
Potential for automation Nil Medium Medium High
cheap and cheap and
Transportability of pre- Costly due to and convenient
convenient due convenient due
basic seed bulkiness due to small size
to small size of to small size of
Current strategies for basic seed tuber production
The conventional method of seed potato production is to repeatedly propagate a sample of tubers which have
been proved to be free of pathogens in a system called clonal multiplication (Bryan, 1981; Struik and Wiersema,
1999). The clonal multiplication system has been been practised effectively in the Netherlands, South Africa
(Haverkort, 2007) and Kenya (Crissman et al., 1993).
The clonal multiplication system as practiced in Kenya is based on the row and plot technique (Figure 1). The
first generation (clone A) consists of minitubers produced either in pots or from an individual
motherplant. Clone A is planted in a single row (the row unit). If any plant tests positive for diseases the entire
row is discraded. The second and third generations (Clone B and C) continue to be seaprated to distinguish the
original motherplant source and are planted in plot units where roguing is done during certication inspections.
This system of seed increase is laborious, expensive and time consuming. Because of a low multiplication rate
(usually 1:6), it takes many years to build significant quantities of seed to meet the demand of the potato
industry. Another constraint is the degeneration of seed stocks from one generation to another due to
accumulation of bacteria, fungi, viruses and viroids. Modern seed programmes tend to minimize use of clonal
systems or use a combination of clonal and rapid multiplication systems.
Rapid multiplication techniques
There are several in vitro and semi-in vivo techniques that multiply healthy planting material rapidly. These
include sprout cuttings, stem cuttings, leaf-bud cuttings, single node cuttings and tissue culture (Ranalli, 1997;
Struik and Wiersema, 1999). The major disdavantage of the first four techniques are that they are heavily
dependent on fuel energy which is used to sterilize the propagation media. Many seed programmes prefer to use
minitubers, defined as the small tubers, (usually 5-25 mm), that can be produced through out the year under
semi-in vivo conditions in glasshouses and screenhouses using in vitro propageted plantlets, planted at high
density. Production of minitubers is a resource and labour intensive operation. Several techniques have been
evaluated and proved suitable for minituber production including aeroponic culture (Kang et al., 1996; Kim et
al., 1999; Nugaliyadde, et al., 2005); hydroponic culture in inert aerated substrate (such as wood, perlite,
vermiculite), in which case irrigation takes place by percolation, drip irrigation and sub-irrigation (Correa et al.,
2009) and nutrient film cultures, i.e. hydroponics systems in which roots grow directly in either a pure
circulating nutrient solution or in a
circulating nutrient solution system with very little substrate (Struik and Wiersema, 1999). In Kenya, techniques
for minituber production that have been used include various types of cuttings and in vitro plantlets planted
either in pots or beds in sreenhouses and glasshouses (Lung’aho et al., 1997).
The case for aeroponics
Aeroponics is an alternative method of soil-less culture in growth-controlled environments (Figures 2-4). The
underground parts are enclosed in a dark chamber and supplied with a nutrient solution by way of a mist device
(Otazu, 2010). Aeroponics optimizes root aeration resulting in a high yield of minitubers compared to
hydroponics (Soffer and Burger, 1988). Additional advantages include limited water use, nutrient recirculation
and good monitoring of nutrients and pH (Figure 1). The aeroponics technique has been used in production of
different horticultural and ornamental seeds (Biddinger et. al., 1998, He and Lee, 1998, Molitor et al., 1999).
An aeroponic system for seed tuber production has been applied successfully in Korea (Kang et al., 1996; Kim
et al., 1999) and China. In Africa, the technology is being pilot tested in several countries including Kenya,
Uganda and Malawi. In Kenya, there are several pilot units at KARI-Tigoni, Genetics Technology International
Limited, Kisima Farm, Suera Farm and Agricultural Development Farm, Molo.
Fig. 2: An aeroponic system for quality seed potato production (Source: Otazu, 2010)
Fig. 3: Foliage development under aeroponics conditions (Source: Otazu, 2010)
Fig. 4: Tuber development under aeroponic conditions (Source: Otazu, 2010)
Although the inhibition of tuberization in immersed organs or organs subjected to continuous mist culture has
been reported (Tibbitts and Cao, 1994), tuberization under these procedures could be promoted under stress
conditions such as N deficiency (Kraus and Marschner, 1982) and short term reductions in nutrient solution pH
(Wan et al., 1994). Ritter et al. (2001) demonstrated that aeroponics minituber production under temperate
weather conditions substantially improved yields. Farran et al. (2006) reported a minituber yield of 800
tubers/m2 at a plant density of 60 plants m2 over a five month period in weekly harvests which translates to a
multiplication rate of 1:13. They also found the field performance of aeroponically produced tubers to be similar
to minitubers produced aeroponically. Research at the International Potato Centre shows that multiplication
rates of 1:100 can be achieved (Otazu, 2010). Harvesting minitubers in aeroponic systems is convenient, clean,
and permits a greater size control through sequential harvesting (Ritter et al., 2001). Lommen and Struik (1992)
found that the number and timing of non-destructive harvests were the key factors in the optimization of
minituber production. A major limitation of aeroponic systems is that they are dependent on the low volume
available to the root system and any losses of power to pumps can produce irreversible damages including
complete loss of plantlets. Additionally, any pathogen infecting the roots can lead to loss of all the plants in a
production unit (Otazu, 2010).
Growers who have planted minitubers indicated that the minitubers are quite delicate in comparison with
conventional seed tubers and that the incidence of rotting can be quite high. They also reported that the
technology of growing the minitubers is lacking.
Conclusion and future prospects
Aeroponics would appear to have a number of potential attributes to make potato production more efficient. The
aeroponics technique has the potential to eliminate all but one generation of seed potato multiplication in the
field thus lowering costs and raising the plant health quality of the first field production generation.
Furthermore, aeroponic systems offer the opportunity to determine the precise fertilizer requirements for the
crop, and thus increase productivity (using drip fertigation), reduce fertilizer use, and reduce the risk of
excessive fertilizer residues moving into the subterranean water table. Important considerations should,
however, be addressed before setting up a commercial system for minituber production. A fully automated
system monitoring both nutrient solution and dynamic parameters, such as concentration, pH, and flow rate
should be incorporated into the system. The system should also be equipped with suitable sensors and alarms to
control electric power, pumping, spraying, and chemical variables. Both the cost of these additional facilities
and such labour-intensive tasks as staking and manual harvesting of plants should be economically assessed
prior to switching to the system. Power generators, solar or wind systems are an absolute necessity especially in
areas with frequent power interruptions. To optimize an aeroponics system, appropriate nutrient solutions, plant
densities, number of harvest and harvesting intervals, as well as possible interactions between them require to be
studied. Agronomic packages for growing mintubers under field conditions need to be optimized.
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