Screening of sweet potato ((Ipomea batatas [L.] Lam.)cultivars for drought tolerance

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International Journal of Environment, Agriculture and Biotechnology (IJEAB) Vol-3, Issue-3, May-June- 2018 ISSN: 2456-1878 Page | 732
Screening of sweet potato ((Ipomea batatas [L.]
Lam.) cultivars for drought tolerance
Vincent Ishola Esan 1*, Oluwafemi Oyeniyi Omilani 1, Sifau Adenike
Adejumo 2 TeniadeOmosebi Adeyemo 1, Oluwafunke Adenike Akinbode3
1Department of Environmental Management and Crop Production, Bowen University, Iwo, Osun State, Nigeria
2Department of Crop Protection and Environmental Biology, University of Ibadan, Ibadan, Oyo State, Nigeria
3Institute of Agricultural Research and Training, Obafemi Awolowo University, Moor plantation, Ibadan, Nigeria
*Corresponding Author
Abstract The effect of drought on most agricultural
crops results inmany problems for the producers in
Nigeria and even other parts of the world. These problems
include reduced vegetative parameters and yield loss
which co nsequently lead to reduced income for the
growers of the crops. The most direct way of avoiding
drought is to discover or create drought tolerant varieties
of sweet potato. Sweet potato is a crop which is part of the
Nigerian diet due to its perceived nutritive values. A field
experiment was carried out in Bowen University, Iwo to
evaluate different cultivars of sweet potato for drought
tolerance. The experimental design was laid in
Randomized Complete Block Design with three replicates
and three treatments including the mild water stress (32
days of drought), severe water stress (from the day of
drought till harvest) and nowater stress (control). Results
showed that under the control treatment, the highest yield
was from the Local variety 1 with 127.63 g while the
lowest yield under control was from Local variety 2 with
39.20 g. Under the mild water stress, the highest yield was
from Introduced va riety 1 with 272.46 g while the lowest
yield was from Local va riety 2 with 59.66 g. Under the
severe water stress, the highest yield was from Local
variety 1 with 41.15 g while the lowest yield was from
Introduced variety 1 with 0 g. The h ighest yield among the
three treatment methods was under the mild water stress
treatment from Introduced variety 1 with 272.46
g.Therefore, variety 3, the local va riety, is recommended
under severe drought based on the above reason but under
moderate drought,the Introduced variety i.e. variety 1
(orange fleshed sweet potato) is preferred becau se it had
the highest yield and is also of high nutrient content
compared to the other varieties.
Keywords drought, field experiment, sweet potato,
Sweet potato (Ipomea batatas [L.] Lam.) is an
economically important crop in the world and particularly
in Nigeria. Sweet potato occupies the p osition of se venth
most important crop in terms of global production and in
developing countries it ranks third in value of production
and fifth in caloric contribution to the human diet [1].
Uganda, Nigeria, Tanzania, Angola, Burundi,
Mozambique, Madagascar, Rwanda and Ethiopia, China,
Indonesia, Viet Nam, India, USA a nd Japan are the top 15
sweet potato producers in the world [2]. It contributes
significantly to the agricultural production of Sub Saharan
Africa countries with roughly 3.2 million hectares and a
production estimated at 13.4 million tons of tubers in 2005
[3]. A lot of root tubers are har vested per unit area and per
unit time duri ng relatively short periods of rain, meaning
that it can withstand occasional drought, and is much more
productive in less fertile soil than crops such as maize [4].
Sweet potato is con sidered as one o f the major sources of
food, animal feed and industrial raw materials. It has a
significant contribution as an energy supplement and a
phytochemical source of nutrition. It pro vides strong
nutrients and ultimately good health to those who eat it. It
possesses anti-carcinogenic and cardiovascular disease
preventing properties [5].
Sweet potato is one of the main foods cultivated
and consumed by most Nigerians.It is not too difficult to
grow and is of great potential industrially and
economically and due to its significance and importance,
sweet potato is increasing in Nigeria’s agriculture and food
systems [6]. According to the survey conducted in six
States in Nigeria by [7], the different forms of sweet potato
utilization are boiling and eating with stew/palm oil,
slicing and frying, roasting, boiling and eating as snack;
boiling and pounding alone or with boiled yam/garri for
eating with soup; cooking alone or with another crop to
make pottage; slicing and sun-drying for milling into flour;
feeding of vines and leaves to livestock; small tuberous
roots as livestock feed; made into fufu like cassava; fresh
leaves and young shoots consumed as vegetable. Also, in
some African countries like Kenya, the storage roots are
boiled and eaten, or chipped, dried and milled into flour
which is then used to prepare snacks and baby weaning
foods [8].
International Journal of Environment, Agriculture and Biotechnology (IJEAB) Vol-3, Issue-3, May-June- 2018 ISSN: 2456-1878 Page | 733
Sweet potato is considered as one of the major
sources of food, animal feed and industrial raw materials.
It has a significant contribution as energ y supplement and
phytochemical source of nutrition. It pro vides strong
nutrients and thereby good health to those who eats it and
possesses anti-carcinogenic and cardiovascular disease
preventing properties [9]. Sweet potato varieties are
outstanding source of vitamin C, B2, B6 and E, as well as
dietary fiber, potassium, copper, manganese and iron, and
are lo w in fat and cholesterol. The root parts of sweet
potato contain 25-30% carbohydrates and 2.5-7.5%
protein. In addition to this, it also supplies 200-300 mg 100
g-1 of potassium, 0.8 mg 100 g-1 of iron (Fe), 11 mg 100 g-1
of calcium (Ca) and 20 -30 mg 100g-1 of vitamin C of its
dry matter [10]. Industrially, Sweet potato yield starch,
natural colorants, and fermented pro ducts such a sbutanol,
acetone, ethanol, wine, and lactic acid [11,12]. Leaves,
stems, roots of sweet potato serve as livestock feed [13].
Leaf protein content of sweet po tato contains twice that
from the storage roots[14].
In spite ofthe high nutritious and economic
potential of sweet potato, it faces with a lot of challen ges
and abiotic and biotic constraints such as drought, low soil
nutrients, weeds, pests, diseases, lac k of post-harvest
storage facilities and improved varieties [15,16]. With
climate change whose signs are already visible,
agricultural pr oduction i s facing alarming threats which
can lead to serious problems of food insecurity [17] and
unprecedented ex treme hunger. Moreover, [18] reported
that, Africa and especially West Africa will be seriously
affected by the deleterious effects of climate c hange. The
variability o f cli mate cha nge and the prevale nce of
extreme events, including drought, are a harsh reality for
small farmers in Africa and in Nigeria who depend
exclusively on rain-fed agriculture. Over the last decade,
environmental stresses have become more frequent and are
exacerbated by a rapid change in climate. It constitutes
perhaps the most momentous environmental challenge of
our time and poses serious threats to sustainable
development worldwide and chiefly in most developing
countries [19]. It has been esti mated that drought is the
most important environmental stresses and represents 70%
of yield losses of cereal crops worldwide [20]. In addition,
drought is regarded as environmental factors that lead s to
about 75% yield loss each year in the world [19]. The 2011
Texas drought has caused a record $5.2 billion in farming
losses, for example, making it the most costly drought on
record [21]. Among different abiotic stresses, drought is by
far the most complex and devastating worldwide [22].
It has been demonstrated that sweet potato crop is
sensitive to water shortage in the course of establishment,
vine development and storage initiation[23]. [24] also
reported that the water scarcity during critical periods of
growth leads to irrep arable consequences on yield.
According to [25] drought is the chief production
limitation of sweet potato in the areas where agriculture
mainly dep endents on rainfall. [26] revealed that water
stress in sweet potato reduces vegetative and yield
parameters in terms of quantity and quality. A variety is
considered as drought resistant when it can produce high
yield under water stress [27].[28]showed that the yield of
most crop s has been used as indicator for drought
tolerance. Henceforth, sweet potato varieties tolerant to
water stress should be able to produce more quantity and
quality yields under drought conditions. This could be
discovered only through screening of sweet potato
genotypes under managed water stress conditions [29].
Thus, identification of cultivar performance under drought
conditions is thus considered to be of vital importance.
Therefore, the aim of this study is to improve stability and
increase production of sweet potato in Nigeria through the
development of drought tolerant cultivars. More
specifically, the objectives are to (1) Evaluate sweet potato
cultivars for drought tolerance under field conditions and
(2) identify sweet potato cultivars withhigh yield and high
Description of the experimental site
The field experiment was carried out on sweet
potato at Bowen University Teaching and Research Farm
Iwo, Osun State, Nigeria. Iwo is a City in Osun State,
Nigeria. The City formerly part of old Oyo State was later
separated and became one of the major townships in Osun
State, Nigeria. It has a latitude of 7° 38' 6.97" N and a
longitude of 4° 10' 53.62" E. Rainfall and te mperatures
data were recorded daily from the date of planting till
Plant material
The material used in this study consisted of four (4) sweet
potato cultivars. Two sweet potato cultivars (local variety
1 and 2) were obtained from Iwo farmers and the two other
cultivars were newly introduced (introduced variety1 and
2). The introduced variety 1 is orange-fleshed cultivar
which has been recognized as good sources of β-carotene,
a precursor of vitamin A.
Experimental design and water stress
The soil was prepared, ploughed, harro wed and ridged. A
Randomized Complete Block Design was used for the
drought experiment. The experimental block unit was 10m
by 2m with twelve beds. Each bed in a block measured 2 m
and the space between rows was 90cm and the space
within a row was 30cm. There were three experimental
blocks in total with 36 beds for the experiment and four
cultivars of sweet potato. Sweet potato vines were cut to
30cm lo ng eac h a nd planted on the 30th of November,
International Journal of Environment, Agriculture and Biotechnology (IJEAB) Vol-3, Issue-3, May-June- 2018 ISSN: 2456-1878 Page | 734
2016 at the rate of six (6 ) vines per experimental unit with
a depth of 15cm at a spacing of 30cm. The soil was
thoroughly watered before planting.
For the firm establishment, sweet potato plants were
watered daily in the evenings for about a month and 11
days i.e. from 1st of December 2016 to 11th of January
From January 12th 2017, there was imposition of water
stress i.e. no watering of treatment 1 and treatment 2 while
the treatment zero which served as control was watered
daily in the evening until harvest. T1 was the mild drought
stress and T2 was the severe moisture stress (no water was
applied till harvest though there was so me rainfalls toward
the end of the experiment). In the mild moisture stress,
drought was imposed for about a month and 6 days that is
from January 12th to February 17th 2017. On the evening of
February 17th, the watering of only T1 (mild drought
stress) resumed again, therefore T0 (Control) and T1
(mild-drought stress) were the only treatments being
watered till the date of harvest which was the 10th of April,
Measurement of vegetative and reproductive
Data were collected on the following parameters;
Vine length- The length of two most vigorous vines
were taken using a measuring tape. The length was
measured from the point of soil contact to the apical
tip. The vines were straightened so as to get
accurate reading.
Petiole length- the stalk of the leaf was measured
from the base of t he leaf to the point of attachment
to the stem.
Leaf length- The length was measured from the tip
of the leaf to the base or bottom of the leaf
Leaf breadth- This was the measurement of the
width of the leaf. The widest part of the bottom was
measured from side to side.
Internode length- This was obtained by measuring
the distance between the nodes of the vines.
Plant height- This was measured with a carpenters
measuring tape, do ne b y putting the tape on the
ground and elongating the tape to check the height
without straightening of the vine.
Fresh weight of the vines per plant: it is the weight
of above ground biomass before drying in the oven
using a scale
Dry weight of the vines after drying in the oven set
at 850C for 4 days was also taken using a scale
Fresh weight of the roots harvested : it is the weight
of all storage roots at harvest per plant
Dry weight of the root: it is weight recorded with a
weighing balance after drying in the oven
Total fresh weight (total yield): It is the total weight
of storage roots
Leaf tissue is most commonly used for RWC3
determination, measured as follows. A sample of
leaf tissue was taken a nd the fresh weight was
immediately determined, followed by flotation on
distill water for up to 4 hours according to methods
of Smart and Bingham (1974). The turgid weight
was then recorded after the 4 hours, and the leaf
tissue was sub sequently oven-dried to a constant
weight at about 750 C for 48 hours. RWC was
calculated by following formula:
Statistical analysis
All data recorded were subjected to statistical analysis
using “R” software to identify significant difference
among the sweet potato cultivars used under the three
treatments. ANOVA was performed for the assessment of
the variation at 0.05 level of probability using Ne wman-
Keuls Multiple Comparison-PostHOC test. In addition,
Pearson correlation coefficient between traits measured
was computed.
The te mperature of Iwo in Osun state was
recorded daily from the 12th of January till 10th of April as
shown in Figure 1.From Jan uary to March, the period was
very hot without recording any single rainfall.
Plant height
The mean plant height readings under the non-stress
treatment are presented in Figure 2. The means for control
ranges from 21.3 to 29.9 cm. The lowest 21.3 cm was
recorded in variety 1 (introduced variety 1) and the highest
29.9 cm was from variety 2. Under the mild water stress,
the readings vary b etween 20.67 and 29 .4 cm. The lowest
20.67 cm was obtained from variety 4 ( Local variety 2)
and the highest 29.4 cm was from variety 2 (introduced
variety 2). Under the severe water stress, the values range
between 16.1 and 25.1. The lowest was 16.1 which was of
variety 3 (Local variety 1) and the highest was 25.1 which
was variety 2 (introduced variety 2). Overall, the mean
plant height values range between 16.1 and 29. 9 cm. The
lowest value was under the severe water stress while the
highest value was under the control treatment. There was
no significant difference between the values obtained from
the control and the mild water stress, but in the severe
water stress there was a significant difference as there was
a reduction in the mean values. Except in the case of
variety 2 (introduced variety 2) which had a value of 25.1