Physiological Characteristics Analysis of Leaves of Several Sweet
Potato (Ipomoea batatas L.) Genotypes on Various Watering Level
Siti Namira, Nini Rahmawati and Lisa Mawarni
Faculty of Agriculture, Universitas Sumatera Utara, Medan 20155, Sumatera Utara, Indonesia.
Keywords: Drought stress, physiological character, sweet potato
Abstract: Drought stress is a major problem in crop production worldwide. The unavailability of groundwater and
erratic climate change causes a lack of water for plants. Efforts that can be made to maintain sweet potato
production in drought conditions are by planting genotypes that are tolerant of drought stress. This research
aim was to determine the growth and production and also to analyze the physiological characters of several
sweet potatoes genotypes on various watering level. The observed parameters were chlorophyll a, b and
total and also relative water content at two months and three months after planting (MAP). The results
showed that sweet potato genotypes had a different response to the level of watering. The response of each
sweet potato genotype was significantly different in the parameters of chlorophyll a, b and total chlorophyll
in the third month and the relative water content at 2 MAP. The Binjai accession genotype had the highest
chlorophyll a, b and total chlorophyll content compared to other genotypes at 3 MAP. Watering levels
treatment significantly affected the chlorophyll a, b and total at 3 MAP. The optimum watering significantly
increases the chlorophyll a, b and total chlorophyll content at 3 MAP.
1 INTRODUCTION
Drought stress is an environmental condition in
which plants do not receive sufficient water intake
hence plants cannot carry out the process of growth
and development optimally. Drought stress is a
major problem in crop production worldwide.
Drought stress is identical to lack of water hence if
plants experience a lack of water, the stomata in the
leaves will close and will result in CO
2
being
blocked to enter and reduce photosynthetic activity
in the plant. In addition, plants will also experience
inhibition in synthesizing proteins and cell walls
(Farooq et al., 2009).
Water requirements of each plant are different,
depending on the type of plant and its growth phase.
Water requirements in plants can be fulfilled with
the absorption of water by the roots. The amount of
water absorbed by roots is very dependent on soil
water content, the ability of soil particles to hold
water and the ability of roots to absorb water
(Song et al., 2010). Plants that experience a lack of
water generally have a smaller size compared to
plants that grow normally. Water shortages can
reduce crop yields very significantly and even can
cause death in plants (Song and Banyo, 2011).
Sweet potatoes are said to be (1) tolerant of
drought: if the decrease in tuber yield is less than
10% against normal watering, (2) moderate
tolerance: if the decrease in tuber yield ranges from
11-20% to normal watering, (3) sensitive: decreased
in tuber yields range from 21-40%, and (4) very
sensitive: a decrease in yield is >40% compared to
normal watering (Chunsheng et al., 1993).
Lizhen (1995) researched two sweet potato
varieties and reported that the critical phase of sweet
potato plants on drought was at the beginning of
growth, i.e. at 1-60 days after planting (DAP). In
general, the phase of tubers formation in sweet
potato ranges from 30–45 DAP. In this phase, if
there is a drought, it will reduce canopy weight, leaf
area, and tuber yield.
Varieties are one of the important technological
components that are easily adopted by farmers. The
planting of sweet potatoes which were intended for
consumption is preferred with varieties that taste
sweet, form a good tuber, and have a low water
content (Yusnita, 2010). Beta-1 is a sweet potato
variety which has a high beta-carotene content,
exceeding the beta-carotene content of 12,032
µg/100gram this is even higher than beta-carotene
levels in carrots. The high content of beta-carotene
Namira, S., Rahmawati, N. and Mawarni, L.
Physiological Characteristics Analysis of Leaves of Several Sweet Potato (Ipomoea batatas L.) Genotypes on Various Watering Level.
DOI: 10.5220/0008552102230228
In Proceedings of the International Conference on Natural Resources and Technology (ICONART 2019), pages 223-228
ISBN: 978-989-758-404-6
Copyright
c
2019 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
223
can be predicted from the color of orange flesh. The
yield potential of this variety reaches 35.7 tons/ha
with a harvest age of 4.0-4.5 months. The
advantages of Beta-1 sweet potato varieties have
high production potential and beta-carotene content
(Jusuf et al., 2008).
With the availability of superior varieties that
have good tolerance to drought, sweet potatoes can
be commercially managed and yield losses and
production costs can be reduced. Sweet potato plant
breeding which aimed at improving tolerance to
drought has not been specifically done in Indonesia
(Jusuf et al., 2005).
Zulkadifta (2018) research showed that the local
sweet potato genotype from Lubuk Pakam resulted
in the number of tubers, tuber length, tuber weight
and harvest index. This was presumably because, in
the local genotype of Lubuk Pakam, the
photosynthesis results were mostly translocated to
tubers hence the production was greater than that of
other genotypes, local genotypes of Lubuk Pakam
and Perbaungan were able to adapt in planting
environment while the Beta 1 genotype from Malang
had to adapt first in planting environment. Local
sweet potato genotype of Perbaungan has higher
tuber weight and harvest index because local
genotypes are able to adapt, grow and produce better
than introduced varieties.
Increasing production of sweet potato plants can
be done through fertilization and watering.
Availability of water is a limiting factor for plant
growth. To fulfill the water needs of the plant and
maintain its availability in the soil and its
distribution, watering is needed. Another component
in increasing production is watering which is an
essential factor for plants (Sari et al., 2016).
The soil moisture required by sweet potato plants
at the beginning of growth ranges from 60-70%, in
the middle of the growth is 70-80%, and the end of
growth requires 60% humidity. However, long
drought duration can inhibit tuber growth hence it
can affect the results (Flach and Rumawas, 1996).
The critical phase of sweet potato in the condition of
water deficit is at the beginning of growth (1-60
DAP). Decrease in canopy weight, leaf area and
tuber yield can occur in these conditions. Loss of
fresh tuber yield due to drought stress is reported
range from 2.53 to 63.52%. The amount of tuber
yield loss depends on the intensity of stresses, the
type of soil and varieties/clones used (Lizhen, 1995).
Rahayuningsih et al., (2000) evaluated 50 sweet
potato clones against drought by normal watering
from planting to harvesting and limited watering
treatment until 1.5 months after planting (MAP).
The results showed that the range of tuber loss was
between 2.53-63.52% in conditions of drought.
Irrigation in sweet potato plants on drought
consisting of three levels of irrigation, namely: P0
(very limited irrigation) = plants were irrigated from
planting to four weeks after planting with an interval
of 10 days, P1 (limited irrigation) = plants were
irrigated from planting to eight weeks after planting
with an interval of 10 days, P2 (optimum irrigation)
= plants were irrigated from planting to harvest with
an interval of 10 days (Hapsari et al., 2011).
Drought in sweet potatoes can cause a decrease in
tendrils length by 25% (60 hst) and 29% (90 hst).
The impact of drought also causes leaf area to
decrease by 30% and tuber weight in very large
categories (> 300g) decreases by 33% (Hapsari and
Mejaya, 2016).
This research aim was to determine the growth
and production and also analyze the physiological
characteristics of several sweet potatoes
(Ipomoea batatas L.) genotypes on various levels of
watering.
2 MATERIALS AND METHODS
2.1 Research Area
The experiment was conducted in April-December
2018 at the experimental field of the Faculty of
Agriculture, Universitas Sumatera Utara, Prof. A.
Sofyan Street, No. 3 Kampus USU, Medan. This
research used a randomized block design with two
factors, the first factor was sweet potato genotype
(Beta-1 superior variety, Perbaungan local
accession, and Binjai local accession) and the
second factor was watering levels, very limited
watering (watered until 1 month with 10 days
interval), limited watering (watered until 2 months
with 10 days interval) and optimum watering
(watered until 4 months with 10 days interval). This
research started from land preparation, planting,
application of watering, tending, fertilizing, and
physiological parameter analysis which includes the
content of chlorophyll a, b, and total and the relative
water content of leaves at Laboratorium Kultur
Jaringan Tanaman, Faculty of Agriculture,
University of Sumatera Utara. Observations were
made in the second and third months after planting.
Watering applications were carried out starting 4
weeks after planting (WAP) up to 9 MST with 10
days intervals.
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2.2 Analysis Procedures of Chlorophyll
a, b and Total Content
The chlorophyll analysis method used in calculating
the amount of chlorophyll a, b and total was the
Wintermans and De Mots method (1965).
Chlorophyll was extracted by crushing the leaves
using 96% ethanol. After that filtered using filter
paper, then the solution was transferred into a test
tube hence 25 ml of leaf extract was obtained.
Prepared UV/VIS spectrophotometer and arranged
the wavelength, inserted 96% ethanol solution
(blank) as neutralizer then released the blank
solution then alternately put the extract solution into
the UV/VIS spectrophotometer. The solution was
measured by a spectrophotometer at wavelengths of
649 nm and 665 nm. Total chlorophyll, chlorophyll
a, chlorophyll b in units of g/mg were calculated
using the formula:
chlorophyll a =
{(13.7 x A665) – (5.76 x A649)}/10 (1)
chlorophyll b =
{(25.8 x A649) – (7.60 x A665)}/10 (2)
Total chlorophyll =
{(6.10 x A665) + (20.0 x A649)}/10 (3)
A665 = absorbance of chlorophyll extract at 665 nm
A649 = absorbance of chlorophyll extract at 649 nm
Analysis of chlorophyll content was carried out
when the plants were 2 months and 3 months old.
2.3 Leaf Relative Water Content
(RWC)
The relative water content of leaves was analyzed
using Prochazkova et. al., (2001) method. Relative
water content was determined by taking 10 pieces of
leaves. The leaf pieces were weighed using an
analytical scale to find out the fresh weight (FW).
Then, hydration was done for 24 hours. After 24
hours weighing was carried out to determine
saturated weight (SW). To find out the dry weight
(DW), the leaf pieces were oven-dried at 80
0
C for 48
hours. The activity of relative water content is
expressed in units of percent. Relative water content
was calculated by the formula:
RWC =
Fresh weight - Dry weight
x 100% (4)
Saturated weight - Dry weight
2.4 Data analysis
Data were analyzed statistically by the F test and
continued by the Duncan Multiple Range Test
(DMRT) at the level of α 5%.
3 RESULTS AND DISCUSSIONS
3.1 Leaf Chlorophyll Content
The data presented in Table 1 showed that the three
genotypes were not significantly different from the
parameters of chlorophyll a, b and total chlorophyll
at 2 MAP. Beta-1 varieties had the highest
chlorophyll a and total chlorophyll content
compared to other genotypes, while the highest
chlorophyll b content was produced by the Binjai
accession genotype. It was suspected that at the
beginning of planting the water content in the
rhizosphere was still sufficient to process the growth
of the three sweet potato genotypes, including the
formation of chlorophyll. Chlorophyll content is
influenced by genetic factors, plant growth rates,
adaptability of plants and the environment. Factors
that influence the formation of chlorophyll include
genes, light, and elements of N, Mg, Fe as forming
and catalyst in the synthesis of chlorophyll. All
green plants contain chlorophyll a and chlorophyll b.
Chlorophyll a composes 75% of total chlorophyll.
Chlorophyll content in plants is about 1% dry weight
(Pratama and Laily, 2015). The formation of
chlorophyll in leaves is most influenced by sunlight,
but the age of the leaves also affects the chlorophyll
content found in a leaf (Hidayat, 2008).
Table 1: The content of chlorophyll a, b and total of
several sweet potato genotypes at 2 MAP.
Genotypes
chlorophyll a
(mg/g)
Total
chlorophyll
(mg/g)
Beta-1 Variety
50,79
25,36
Perbaungan
accession
43,82
22,27
Binjai
accession
28,34
15,78
Plants that are able to adapt in one environment
will have a higher chlorophyll content than plants
that are unable to adapt. The data presented in Table
2 showed that the chlorophyll content was
significantly different in each genotype at 3 MAP.
The Binjai accession genotype had the highest
chlorophyll a, b and total content compared to other
genotypes. This was because the Binjai local
accession genotype has good adaptability even
though it was planted in a different environment
from its origin. Jusuf et al., (2008) stated that
varieties/clones/genotypes that are broadly adapted
have the advantage of being able to produce high
yields on diverse agroecosystems. Chipungu et. al.,
(2018) also stated that environmental factors such as
Physiological Characteristics Analysis of Leaves of Several Sweet Potato (Ipomoea batatas L.) Genotypes on Various Watering Level
225
soil type, soil pH, altitude, planting season, and
temperature greatly influenced the tuber yield when
compared with genotype and genotypic and
environmental interactions.
Table 2: Chlorophyll a, b and total content of several
sweet potato genotypes at 3 MAP.
Genotypes
chlorophyll a
(mg/g)
chlorophyll b
(mg/g)
Total
chlorophyll
(mg/g)
Beta-1 Variety
13,74c
12,59c
7,29c
Perbaungan
Accession
17,83b
15,91b
9,42b
Binjai
Accession
23,18a
20,82a
12,26a
Description: The numbers followed by the different
letters in the rows in each average show
significantly different based on Duncan’s
Multiple Range Test at the level of α = 5%.
The data presented in Table 3 showed that the
watering level treatments did not significantly affect
the content of chlorophyll a, b and total chlorophyll
at 2 MAP. The need for water for the formation of
chlorophyll is still sufficient for plants hence the
process of chlorophyll formation had not been
disturbed. Research by Hendriani and Setiari (2009)
also showed that the content of chlorophyll a, b and
total in long bean leaves (Vigna sinensis) is not
significantly different at various levels of watering.
Table 3: The effect of several watering level treatment on
chlorophyll a, b and total content at 2 MAP.
Watering
Levels
chlorophyll a
(mg/g)
chlorophyll b
(mg/g)
Total
chlorophyll
(mg/g)
Very Limited
Watering
49,18
30,60
24,81
Limited
Watering
39,55
30,42
20,47
Optimum
Watering
34,22
31,14
18,13
The data presented in Table 4 showed that the
watering levels had a significant effect on
chlorophyll a, b and total content at 3 MAP. The
optimum watering level had the highest chlorophyll
a, b and total content compared to other treatments.
In the optimum watering treatment, which was
watered until 4 months old with 10 days interval, the
planting medium had sufficient water content to
meet the water needs of plants to grow well and
perform various metabolic activities such as
photosynthesis. Rahayuningsih et al. (2000) stated
that the chlorophyll content tends to decrease in line
with the length of the time interval for watering.
Fitter and Hay (1991) also stated that lacking or
excessive water condition resulting in disruption of
plant physiological process, or can cause plants to
become stressed and if it lasts for a long time, plants
will experience wilting even die.
Table 4: The effect of several watering levels on
chlorophyll a, b and total content at 3 MAP.
Watering levels
Chlorophyll
a (mg/g)
Chlorophyll b
(mg/g)
Total
chlorophyll
(mg/g)
Very Limited
Watering
15,04c
13,25c
7,93c
Limited
Watering
18,66b
16,70b
9,86b
Optimum
Watering
21,05a
19,37a
11,17a
Description: The numbers followed by the different
letters in the rows in each average show
significantly different based on Duncan’s
Multiple Range Test at the level of α = 5%.
3.2 Leaf Relative Water Content
(RWC)
The data presented in Table 5 showed that the leaf
relative water content was significantly different in
the three sweet potato genotypes at 2 MAP. The
Binjai accession genotype had the highest relative
water content of 42.66% compared to other
genotypes. It was suspected that the Binjai accession
genotype had a better ability to adapt in its growth
environment than other genotypes hence it can
develop a better root system to absorb water and
maintain the leaf relative water content.
Whereas three months after planting, the relative
water content of the leaves in the three genotypes
was not significantly different. It was suspected that
the three genotypes had similar adaptive abilities in
line with the increasing age of the plants. The
research results of Khalili et al. (2011) reported that
relative water content is affected by season and
irrigation hence drought stress can reduce the
relative water content significantly. Plants that have
a relative water content between 18.6 - 21.8%.
Furthermore, it was said that the difference in
relative water content ranging between 18.6% and
21.8% is the plant genotype which is most resistant
to drought stress. Fitri and Salam (2017) also stated
that in sufficient water conditions the development
of roots will be perfect and can absorb available
nutrients hence it can increase plant growth, but if
there is a lack of water, the growth will be hampered
ICONART 2019 - International Conference on Natural Resources and Technology
226
especially in the vegetative phase. The existence of
sufficient water during plant growth resulted in the
process of nutrients absorption and the rate of
photosynthesis going smoothly hence it can increase
plant growth.
Table 5. Leaf relative water content of several sweet
potato genotypes at 2 and 3 MAP.
Genotypes
Relative Water Content (%)
Two Months
After Planting
Three Months
After Planting
Beta-1 Variety
29,47c
44,48
Perbaungan
Accession
38,13b
42,17
Binjai Accession
42,66a
42,99
Description: The numbers followed by the different
letters in the rows in each average show
significantly different based on Duncan’s
Multiple Range Test at the level of α = 5%.
Whereas three months after planting, the relative
water content of the leaves in the three genotypes
was not significantly different. It was suspected that
the three genotypes had similar adaptive abilities in
line with the increasing age of the plants. The
research results of Khalili et al. (2011) reported that
relative water content is affected by season and
irrigation hence drought stress can reduce the
relative water content significantly. Plants that have
a relative water content between 18.6 - 21.8%.
Furthermore, it was said that the difference in
relative water content ranging between 18.6% and
21.8% is the plant genotype which is most resistant
to drought stress. Fitri and Salam (2017) also stated
that in sufficient water conditions the development
of roots will be perfect and can absorb available
nutrients hence it can increase plant growth, but if
there is a lack of water, the growth will be hampered
especially in the vegetative phase. The existence of
sufficient water during plant growth resulted in the
process of nutrients absorption and the rate of
photosynthesis going smoothly hence it can increase
plant growth.
Table 6: The effect of several watering levels on the leaf
relative water content at 2 and 3 MAP.
Watering Levels
Relative Water Content (%)
2 months after
planting
3 months after
planting
Very Limited
Watering
39,22
46,01
Limited Watering
35,87
42,78
Optimum Watering
35,17
40,86
Table 6 showed that the watering levels had no
significant effect on the parameters of leaf relative
water content at 2 and 3 MAP. Plants with very
limited watering treatment had a high leaf relative
water content compared to other watering levels.
This was because the value of relative water content
is inversely proportional to the potential of leaf
water, where in plants that get drought stress,
namely at very limited watering levels, will
experience more severe stress due to the amount of
water used by plants to maintain osmotic pressure
and transpiration are greater hence the water
potential decreases. Correspondingly, Makbul et al.
(2011) reported that the response of plants to
drought is very complex, including several changes
as a step of adaptation. Furthermore, it is stated,
drought stress is the status of water in plants that can
be known by measuring the potential of leaf water
and relative water content as physiological
indicators. Water status on leaves, usually an
interaction between leaf water potential and stomatal
conductance, in which drought will induce root
signals to the canopy to reduce the rate of
transpiration hence the stomata closes when the
water supply decreases. High relative water content
is a mechanism of plant resistance to drought, and
this is the result of excessive osmotic regulation or a
reduction in the elasticity of cell wall tissue.
4 CONCLUSIONS
The three sweet potato genotypes had chlorophyll a,
b and total contents which were significantly
different when the plants were at three months after
planting. While the leaf relative water content in the
three genotypes was significantly different at two
months after planting. Binjai accession sweet potato
genotype had the highest chlorophyll a, b and total
chlorophyll content compared to other genotypes at
3 MAP. The treatment of watering levels
significantly affected the chlorophyll a, b and total
content at 3 MAP. Watered plants with optimum
watering levels had the highest chlorophyll a, b and
total content at 3 MAP, while plants with very
limited watering treatment had the highest leaf
relative water content at 2 and 3 MAP.
Physiological Characteristics Analysis of Leaves of Several Sweet Potato (Ipomoea batatas L.) Genotypes on Various Watering Level
227
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