Article

Reduction of Potassium Supply Alters the Production and

Quality Traits of Ipomoea batatas cv. BAU Sweetpotato-5 Tubers
Shaila Sharmin 1 , Md. Nazmul Hasan Arfin 1 , Abu Musa Md Main Uddin Tareque 2 , Abdullah Al Kafi 1 ,
Md. Shohidullah Miah 1 , Md. Zakir Hossen 3 , Md. Abdus Shabur Talukder 1 and Arif Hasan Khan Robin 2, *

1 College of Agricultural Sciences, International University of Business Agriculture and Technology,

Dhaka 1230, Bangladesh; shaila.sharmin@iubat.edu (S.S.); nazmularfin45@gmail.com (M.N.H.A.);
abdullahalkafi78@gmail.com (A.A.K.); drshohidullah@iubat.edu (M.S.M.); shabur.ag@iubat.edu (M.A.S.T.)
2 Department of Genetics and Plant Breeding, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh;
tareque.20220729@bau.edu.bd
3 Department of Agricultural Chemistry, Bangladesh Agricultural University, Mymensingh 2202, Bangladesh;
zakirhm.ac.bau@gmail.com
* Correspondence: gpb21bau@bau.edu.bd

Abstract: In Bangladesh, sweetpotato is the fourth most important source of carbohydrates behind
rice, wheat, and potatoes. Potassium is vital for sweetpotato growth, boosting tuber size, sweetness,
disease resistance, and yield quality, with deficiencies leading to poor tuber formation and increased
stress susceptibility. The present study evaluated the effect of varying dosages of potassium fertilizer
(Muriate of Potash, MoP) on the growth, yield, and biochemical qualities of sweetpotato. As a genetic
material, BAU sweetpotato-5 was chosen as it is recognized for its high yield, short duration, and
nutritional advantages. There were three treatments—full dosage of MoP (321.6 kg ha−1 , T0 ), half
dosage of MoP (160.8 kg ha−1 , T1 ) and no MoP (T2 ). Four replications of a randomized complete block
design (RCBD) were used in the experiment. According to analysis of variance, the morphological
and biochemical parameters, such as the fresh weight plant−1 , number of tuber plant−1 , chlorophyll
Citation: Sharmin, S.; Arfin, M.N.H.; content, total phenolic content, vitamin C, carotenoid, anthocyanin, Zn, and Fe content varied
Tareque, A.M.M.M.U.; Kafi, A.A.; significantly among treatments. The application of the full recommended dosage of MoP resulted in
Miah, M.S.; Hossen, M.Z.; Talukder, the highest values for several traits, including the fresh weight plant−1 , number of tuber plant−1 ,
M.A.S.; Robin, A.H.K. Reduction of chlorophyll content, carotenoid, anthocyanin, and Fe content. Conversely, total phenolic content and
Potassium Supply Alters the
vitamin C were highest without MoP application. Principal component analysis (PCA) differentiated
Production and Quality Traits of
treatment T0 from T1 and T2 due to higher positive coefficients of the number of leaves at 115 days
Ipomoea batatas cv. BAU Sweetpotato-5
after transplantation, vine length at 115 days after transplantation, number of branches, stem diameter,
Tubers. Stresses 2024, 4, 883–895.
https://doi.org/10.3390/
fresh weight plant−1 , tuber length, tuber diameter, tuber weight, number of tuber plant−1 , SPAD,
stresses4040059 carotenoid, anthocyanin, Fe, and negative coefficients of total phenolic content, vitamin C, and
Zn. The findings suggest that potassium is integral to maximizing both yield and key nutritional
Academic Editor: Monica Ruffini
components in sweetpotato cultivation.
Castiglione

Received: 18 November 2024 Keywords: sweetpotato; nutritional components; potassium deficiency; tubers; carotene
Revised: 6 December 2024
Accepted: 9 December 2024
Published: 11 December 2024
1. Introduction
Sweetpotato (Ipomoea batatas), a member of the Convolvulaceae family, is a significant
Copyright: © 2024 by the authors.
root crop mostly cultivated in tropical and subtropical regions of Asia, the tropical Americas,
Licensee MDPI, Basel, Switzerland. the Pacific Islands, and Papua New Guinea [1]. To date, sweetpotato is the seventh most
This article is an open access article important global agricultural crop, producing 86.41 million metric tons globally [2]. It
distributed under the terms and has a wide range of adaptability, making production possible in marginal agricultural
conditions of the Creative Commons settings. This adaptability has made the sweetpotato incredibly important for food security
Attribution (CC BY) license (https:// in developing countries. Globally, more than 95 percent of sweetpotatoes are cultivated in
creativecommons.org/licenses/by/ developing countries, where both the leaves and tubers are consumed by people and used
4.0/). as feed for livestock [3].

Stresses 2024, 4, 883–895. https://doi.org/10.3390/stresses4040059 https://www.mdpi.com/journal/stresses

Stresses 2024, 4 884

In Bangladesh, sweetpotato is the fourth most important source of carbohydrates

after rice, wheat, and potato, with a production of 304 kilo tons in 2022, which was 8.55%
more than in the previous year [4,5]. This is largely due to the introduction and adoption
of modern varieties developed by the Bangladesh Agricultural Research Institute (BARI)
and agricultural universities, along with improved cultivation techniques and increased
awareness among sweetpotato growers. The crop also significantly boosts farmers’ incomes
in Bangladesh [5].
As a sustainable crop, sweetpotato is used to make various high-quality, nutritionally
enhanced food products that support human health. It is rich in vitamins and minerals,
including ß-carotene, anthocyanins, and beneficial fibers [6]. The antioxidantive, vitamin,
and mineral contents of sweetpotato make it a “superfood”. Calorie-wise, sweetpotato is
an ideal food [7].
BAU sweetpotato-5, a high-yielding variety, recently developed by Bangladesh Agri-
cultural University, produces 30–35 tons per hectare with a short growth period. On
average, each tuber’s weight is 200–300 g [8].
Potassium (K) is an essential macronutrient that plays a significant role in the growth
and development of sweetpotatoes. In Bangladesh, Muriate of Potash (MoP) is mainly
applied to the field as a source of K. Bangladesh requires around 0.75 million metric tons of
MoP fertilizer each year [9].
Sweetpotato, sugarcane and cassava have high potassium requirements because their
leaves, vines, stems, and tubers typically extract a significant amount of K from the soil.
Potassium is crucial for photosynthesis and energy transfer. It regulates the opening and
closing of the stomata, which facilitates gas exchange and optimizes the photosynthetic
process. Enhanced photosynthesis leads to increased carbohydrate production, which is
vital for tuber development [10,11]. Moreover, it helps to regulate water use efficiency and
turgor pressure within plant cells. It aids in osmoregulation, which is particularly important
for sweetpotatoes that can experience water stress. Adequate potassium enhances drought
tolerance and overall plant vigor [12]. Furthermore, potassium promotes root development
and is essential for the proper formation and quality of sweetpotato tubers. Strong root
systems enhance nutrient and water uptake, which is essential for healthy growth and
higher yields [13]. Besides, potassium enhances the uptake of other essential nutrients, such
as nitrogen and phosphorus. This synergistic effect leads to improved plant health, growth,
and ultimately, yield [14]. In addition, adequate potassium levels strengthen plant tissues,
enhancing resistance to diseases and pests. This is particularly important for sweetpotatoes,
which can be susceptible to various pathogens [15].
However, potassium deficiency in sweetpotatoes can severely impact plant health,
yield, and quality. The effects of potassium deficiency are noticeable through various
symptoms. First of all, potassium-deficient sweetpotatoes typically show chlorosis, visually
observed as yellowing along the leaf margins of older leaves, which can progress to
necrosis [16]. Secondly, deficiency in potassium can lead to smaller tubers, lower starch
content, and reduced dry matter, which negatively impacts both the quality and yield
of sweetpotato crops. This also reduces the marketability and nutritional value of the
produce [17]. Thirdly, potassium-deficient plants are more vulnerable to pest infestations
and diseases like Alternaria leaf spot and root rot. Studies have shown that adequate
potassium can reduce the incidence of disease and improve plant resilience [13]. Finally,
potassium deficiency can result in weaker, less developed roots, limiting the plant’s capacity
to absorb water and other essential nutrients, further exacerbating growth issues [18].
Potassium is a macronutrient which is essential for the tuber development of sweet-
potato; the impact of a reduced K supply may alter production and biochemical qualities of
sweetpotato tubers. Hence, the incorporation of MoP fertilizer in sweetpotato plant pro-
duction holds significant potential for improving yield quantity and quality. Consequently,
this study assessed the comprehensive effects of MoP fertilizer on shoot morphology, tuber
production and biochemical qualities of sweetpotato variety BAU sweetpotato-5.
Stresses 2024, 4 885

2. Results
2.1. Analysis of Variance
According to the analysis of variance, there were significant variations among treat-
ments for the morphological traits, namely the fresh weight plant−1 and the number of
tuber plant−1 (Table 1). The treatment mean sum of squares was significant at 5% level
(p ≤ 0.05) for the aforementioned traits. The highest fresh weight plant−1 was obtained
when full dosage of MoP was applied (T0 ) (Table S1, Figure 1). This value decreased
significantly by 41.7% and 48.5% in T1 and T2 , respectively, with the decrease in MoP
fertilizer. Similarly, T0 treatment received the highest number of tuber plant−1 . T1 and
T2 treatment decreased the number of tuber plant−1 by 18.5% and 29.63%, respectively,
(Table S1, Figure 1).

Table 1. Analysis of variance (mean squares) for morphological and biochemical traits of BAU
sweetpotato-5.

df Mean Squares
Characters p Value
Treatment Error Treatment Error
30 DAP 9.04 2.85 0.090
Number of 60 DAP 109.7 325.3 0.722
leaves
90 DAP 6.14 1467.38 0.996
115 DAP 112.3 1613.7 0.933
30 DAP 3.02 14.03 0.811

Vine 60 DAP 315.0 307.9 0.398

length 90 DAP 496.8 532.9 0.429
115 DAP 215.2 930.3 0.798
Number of branches 0.64 0.52 0.335
Stem diameter 0.02 0.005 0.062
Fresh weight plant−1 71534* 15312 0.041
Tuber length 13.28 7.06 0.207
Tuber diameter 2 9 2.048 1.44 0.290
Tuber weight 14316 8865 0.252
Number of tuber plant−1 4.08 * 0.94 0.048
SPAD 85.23 * 14.43 0.023
Total phenolic content 36.334 * 6.56 0.027
Vitamin C 36.557 ** 2.21 0.001
Carotenoid 0.0066 ** 0.00078 0.009
Anthocyanin 2.121 ** 0.1535 0.002
Glucose 0.63 2.04 0.741
Fructose 2.23 1.30 0.233
Sucrose 3.003 2.104 0.290
Zn 9.99 *** 0.135 <0.001
Fe 3819.53 *** 1.37 <0.001
*, **, and *** indicate significant at 5%, 1%, and 0.1% levels of probability, respectively. Here, df: degrees of
freedom, DAP: days after transplanting.

Furthermore, there were notable variations among the treatments for the biochemical
traits such as chlorophyll content (SPAD), TPC (mg 100 g−1 fresh tuber), vitamin C (mg
100 g−1 fresh tuber), carotenoid (mg 100 g−1 fresh tuber), anthocyanin (mg 100 g−1 fresh
 2. Results
2.1. Analysis of Variance
According to the analysis of variance, there were significant variations among treat-
Stresses 2024, 4 ments for the morphological traits, namely the fresh weight plant−1 and the number of tuber
886
plant (Table 1). The treatment mean sum of squares was significant at 5% level (p ≤ 0.05) for
-1

the aforementioned traits. The highest fresh weight plant−1 was obtained when full dosage
of MoP was applied (T0) (Table S1, Figure 1). This value decreased significantly by 41.7%
Stresses 2024, 4, FOR PEER REVIEWtuber), Zn (mg kg−1 ), and Fe (mg kg−1 ) content (Table 1). The analysis of variance in this
and 48.5% in T1 and T2, respectively, with the decrease in MoP fertilizer. Similarly, T0 treat-4
study revealed that the treatment difference was significant at 5% (p ≤ 0.05), 1% (p ≤ 0.01),
ment received the highest number of tuber plant−1. T1 and T2 treatment decreased the num-
and 0.1%
ber of tuber ≤ 0.001)
(p plant−1 byfor theand
18.5% biochemical traits.
29.63%, respectively, (Table S1, Figure 1).
Glucose 0.63 2.04 0.741
Fructose 2.23 1.30 0.233
Sucrose 3.003 2.104 0.290
Zn 9.99 *** 0.135 <0.001
Fe 3819.53 *** 1.37 <0.001
*, **, and *** indicate significant at 5%, 1%, and 0.1% levels of probability, respectively. Here, df:
degrees of freedom, DAP: days after transplanting.

Furthermore, there were notable variations among the treatments for the biochemical
traits such as chlorophyll content (SPAD), TPC (mg 100 g−1 fresh tuber), vitamin C (mg
100 g−11.
Figure 1.fresh tuber),
Variation
Variation among carotenoid
amongthree
(mg 100
threetreatments
treatments 0g= 321.8
(T(T−1 fresh tuber), anthocyanin
kg MoP ha−1, T− 1 =
1 160.8 kg (mg
MoP100MoP
kgha
gand
−1 −1 fresh
haT−2 1= and
Figure 0 = 321.8 kg MoP ha , T1 = 160.8
tuber),
0.0 kg MoPZn ha(mgfor
−1
kg−(a)
−1
1 ),fresh
andweight
Fe (mgplantkg ) (g)
−1
−1 content
and− 1(b)(Table
number 1).ofThe analysis
tuber plant of variance
−1.
− 1 in this
T2 = 0.0 kg MoP ha for (a) fresh weight plant (g) and (b) number of tuber plant .
study revealed that the treatment difference was significant at 5% (p ≤ 0.05), 1% (p ≤ 0.01),
Table 1. Analysis
and Chlorophyll
0.1% (p ≤ 0.001)of variance (mean squares)
for the(SPAD)
biochemical for morphological and biochemical traits of BAU
content variedtraits.
among the treatments with T0 having the highest
sweetpotato-5.
SPADChlorophyll
value (Table content
S2). (SPAD)
With the varied amongof
reduction theKtreatments
supply, the with
SPADT0 having
valuethewas highest
reduced
SPAD value (Table S2).
by 8% in T1 and 22% in T2 (Figure With the reduction of K supply,
df S1). On the other Mean the SPAD
Squares
hand, value was reduced
total phenolic content byand
8% in T Characters
1 and 22% in T2 (Figure S1). On the other hand, total phenolic content and p Value
vitamin
vitamin C were the highestTreatment when no MoP Error Treatment
application existed (T2Error
) (Table S2, Figure 2). With
C were the highest when no MoP application existed (T2) (Table S2, Figure 2). With the
the increase in 30 potassium
DAP supply, these two values decreased significantly
9.04 2.85 and reached
0.090
increase in potassium supply, these two values decreased significantly and reached the
the lowest in
Number of 060 DAPT , both reduced by 31% (Figure 2). However,
109.7 carotenoid
325.3 and anthocyanin
0.722
lowest in T0, both reduced by 31% (Figure 2). However, carotenoid and anthocyanin had
hadleaves
different trends.
90 DAP Both carotenoid and anthocyanin 6.14 had their highest value,
1467.38 0.996 with the
different trends. Both carotenoid and anthocyanin had their highest value, with the high-
highest potassium 115 applied (T0 ). Carotenoid had its 112.3
DAP lowest value1613.7 at T1 with a 45% 0.933 reduction
est potassium applied (T0). Carotenoid had its lowest value at T1 with a 45% reduction
while T2 received 30 DAPthe lowest for anthocyanin with a 35% reduction (Table S2, Figure 2).
while T2 received the lowest for anthocyanin with a3.02 35% reduction 14.03
(Table S2, 0.811
Figure 2).
Zinc (Zn) content 60 was was highest in T 1 and
DAPhighest in T1 and lowest in T0 with lowest in T 0 with a 25%
315.0a 25% reduction, reduction,
307.9 while Fe 0.398 while Fe
Zinc (Zn) content content
Vine length
content was highest in T and by reducing it by 46.7%, the value reached the lowest in T
was highest in 90 and by0,reducing it by 46.7%, the value
T0, DAP 496.8 reached532.9 the lowest in0.429T1 (Table 1
(Table S2, Figure
S2, Figure 3). 115 DAP 3).
215.2 930.3 0.798
Number of branches 0.64 0.52 0.335
Stem diameter 0.02 0.005 0.062
2 9
Fresh weight plant −1 71534* 15312 0.041
Tuber length 13.28 7.06 0.207
Tuber diameter 2.048 1.44 0.290
Tuber weight 14316 8865 0.252
Number of tuber plant−1 4.08 * 0.94 0.048
SPAD 85.23 * 14.43 0.023
Total phenolic content 36.334 * 6.56 0.027
Vitamin C 36.557 ** 2.21 0.001
Carotenoid 0.0066 ** 0.00078 0.009
Anthocyanin 2.121 ** 0.1535 0.002

Figure 2. Variation among three treatments (T0 = 321.8 kg MoP ha−1, T−

Figure 2. Variation among three treatments (T0 = 321.8 kg MoP ha1 =1 ,160.8
T1 = kg MoP ha−1 and T−2 1=
160.8 kg MoP ha and
0.0 kg MoP ha−1 for (a) TPC (Total phenolic content, mg 100 g−1 fresh tuber), (b) vitamin C (mg 100
T2−1= 0.0 kg MoP ha−1 for (a) TPC (Total−1 phenolic content, mg 100 g−1 fresh tuber), (b) vitamin C
g fresh tuber), (c) Carotenoid (mg 100 g fresh tuber), (d) Anthocyanin (mg 100 g−1 fresh tuber).
(mg 100 g fresh tuber), (c) Carotenoid (mg 100 g fresh tuber), (d) Anthocyanin (mg 100 g−1
− 1 − 1

fresh tuber).
Stresses 2024, 4, FOR
Stresses PEER
2024, 4 4, REVIEW 5
Stresses 2024, FOR PEER REVIEW 5 887

Figure 3.Figure
Variation
Figure among three
3. Variation among treatments (T0 = 321.8
three treatments (T0 =kg
(T0 =MoP
321.8 kgha
321.8 kg, MoP
−1 Tha
MoP 1 = 160.8
ha−1 kg, T1MoP ha−1kg
and
ha−1Tand
2 = T−
−1, T1 = 160.8 kg MoP 2 =
3. Variation among three treatments = 160.8 MoP ha 1 and
0.0 kg MoP
0.0ha0.0for
kg
kg (a)
MoP ha Znha content
−1 for (mg kgcontent
), (b) Fe content
kg−1 ),(mg
(b) kg ).
−1 −1 for (a) Zn content−1(mg kg −1), (b) Fe content (mg
−1 kg −1).
T = 2 MoP (a) Zn (mg Fe content (mg kg−1 ).
2.2.
2.2. Trait2.2. Trait Association
Association
Association
Trait
The correlation
The correlation
The correlation coefficients
coefficients amongamong
coefficients different
amongdifferent morphological
morphological
different and biochemical
and biochemical
morphological traitstraits
and biochemical are aretraits
displayed in Figure 4. The correlation analysis indicated that out of 110 associations, 8
displayed areindisplayed
Figure 4.inThe correlation
Figure analysis indicated
4. The correlation analysisthat out ofthat
indicated 110 out
associations, 8
of 110 associations,
associations were significant. Five associations were positively correlated, and three were
associations were significant.
8 associations Five associations
were significant. were positively
Five associations were correlated,
positivelyand three were
correlated, and three
negatively correlated (Figure 4). Anthocyanin had a positive significant correlation with
negatively
were correlated
negatively (Figure 4). Anthocyanin
correlated had a positivehad
(Figure 4).−1 Anthocyanin significant
a positivecorrelation
significantwith correlation
tuber diameter and fresh weight plant . Furthermore, vine length at 115 DAP and carot-
tuber diameter
with tuber anddiameter
fresh weight plant−1weight
and fresh plant−1 . vine
. Furthermore, length at vine
Furthermore, 115 DAP
length and at carot-
115 DAP and
enoid were positively correlated with each other and stem diameter (Figure 4). Vitamin C
enoid were hadpositively
carotenoid were correlated
a significant negativewith
positively each other
correlated
correlation withand
with
thestem
each diameter
other
number
and stem
of tuber(Figure
plant−14).
diameter Vitamin
(Figure
. In
4).CVitamin
addition, the
− 1
had a significant
number ofnegative
branchescorrelation
C had a significant
and numberwith
negative correlation the with
of leavesnumber of tuber
the number
at 115 DAP
ofplant
tuber. plant
−1
were negatively Incorrelated
addition, the Zn the
. In addition,
with
numbernumber
of branches
and and number
of branches
Fe, respectively of 4).
and number
(Figure leavesofatleaves
115 DAP were
at 115 DAP negatively correlated
were negatively with Znwith Zn
correlated
and Fe, respectively (Figure (Figure
and Fe, respectively 4). 4).

Figure 4. Correlation coefficients among morphological and biochemical traits of BAU sweetpotato-
5. Here, NL 115 DAP: number of leaves 115 days after transplanting, VL115 DAP: vine length 115
days after transplanting, NB: number of branches, SD: stem diameter (cm), FWP: fresh weight
Figure 4.Figure
Correlation coefficients
4. Correlation among morphological
coefficients and biochemical
among morphological traits of traits
and biochemical BAU of sweetpotato-
BAU sweetpotato-5.
plant−1 (g), TL: tuber length (cm), TD: tuber diameter (cm), TW: tuber weight (g), NTP: number of
5. Here, NL 115 DAP:
Here, NL 115 number of leaves 115 days after transplanting, VL115 DAP:
DAP: number of leaves 115 days after transplanting, VL115 DAP: vine vine length 115 115 days
length
tuber plant−1, TPC: total phenolic content (mg 100 g−1 fresh tuber), Vit-C: vitamin C (mg 100 g−1 fresh
days after transplanting,
after NB: number of branches, SD: stem diameter (cm), FWP: fresh weight
transplanting, NB: number of branches, SD: stem diameter (cm), FWP: fresh weight plant−1 (g),
tuber).
plant−1 (g), TL: tuber
TL: tuber length
length (cm),
(cm), TD:TD: tuber
tuber diameter
diameter (cm),(cm),
TW: TW:
tubertuber weight
weight (g), NTP:
(g), NTP: number number of plant−1 ,
of tuber
tuber plant−1, TPC: total phenolic content (mg 100 − 1 g−1 fresh tuber), Vit-C: vitamin C (mg 100 − 1g−1 fresh
TPC: total phenolic content (mg 100 g fresh tuber), Vit-C: vitamin C (mg 100 g fresh tuber).
tuber).
Stresses 2024, 4 888

Principal component analysis (PCA) identified the most significant relationships

among the morphological and biochemical traits in this study. The first three principal
components (PC) explained 77.5% of the total data variation for the effect of treatments on
morphological and biochemical traits. PC1, PC2, and PC3 explained 45.4%, 19.9% and 12.2%
data variation, respectively (Table 2). The eigenvalues of the first three PCs were greater
than one.

Table 2. Coefficients of principal components for morphological and biochemical traits of BAU
sweetpotato-5.

Variable PC1 PC2 PC3

NL 115 DAP −0.421
0.189 0.154
VL 115 DAP −0.282
0.238 0.243
NB −0.161
0.234 0.421
SD 0.259
0.217 −0.017
FWP −0.055
0.355 0.032
TL −0.244
0.239 −0.250
TD −0.228
0.305 0.104
TW −0.212
0.306 −0.019
NTP 0.223
0.228 −0.286
SPAD −0.019
0.259 −0.270
TPC −0.193
0.058 0.246
Vit-C −0.250
−0.191 0.255
Carotenoid 0.196
0.369 0.054
Anthocyanin 0.308
0.221 −0.166
Zn −0.231
−0.347 −0.298
Fe 0.113
0.336 0.515
% variation explained 45.4
19.9 12.2
p value 0.007
0.093 0.001
Here, NL 115 DAP: number of leaves 115 days after transplanting, VL115 DAP: vine length 115 days after
transplanting, NB: number of branches, SD: stem diameter (cm), FWP: fresh weight plant−1 (g), TL: tuber length
(cm), TD: tuber diameter (cm), TW: tuber weight (g), NTP: number of tuber plant−1 , TPC: total phenolic content
(mg 100 g−1 fresh tuber), Vit-C: vitamin C (mg 100 g−1 fresh tuber).

The first principal component (PC1) explained the highest variation (45.4%) of the
data, with strong positive coefficients for the morphological and biochemical traits, namely
number of leaves at 115 DAP, vine length at 115 DAP, number of branches, stem diameter,
fresh weight plant−1 , tuber length, tuber diameter, tuber weight, number of tuber plant−1 ,
SPAD, carotenoid, anthocyanin, and Fe and negative coefficients of total phenolic content,
vitamin C, and Zn. PC1 showed a highly significant difference among treatments (Table 2).
Stresses 2024, 4, FOR PEER REVIEW The PC1 clearly separated treatment T0 from T1 and T2 in terms of morphological7and
biochemical traits, as evidenced by their differential location in the biplot (Figure 5).

0
2 T2 Fe

TPC
NB

1 Carotenoid
Vit-C VL 115 DAP
SD
T0
PC2 (19.9%)

FWP
0 0
Anthocyanin
TD
NTP
TW

-1 SPAD
Zn

TL
NL 115 DAP
-2
T1

-4 -3 -2 -1 0 1 2 3 4
PC1 (45.4%)

Figure 5.
Figure 5. Biplot
Biplot for
formorphological
morphologicaland
andbiochemical
biochemicaltraits of BAU
traits sweetpotato-5.
of BAU Here,
sweetpotato-5. NL 115
Here, NLDAP:
115 DAP:
number of leaves 115 days after transplanting, VL115 DAP: vine length 115 days after transplanting,
number of leaves 115 days after transplanting, VL115 DAP: vine length 115 days after transplanting,
NB: number of branches, SD: stem diameter (cm), FWP: fresh weight plant−1 (g), TL: tuber length
(cm), TD: tuber diameter (cm), TW: tuber weight (g), NTP: number of tubers plant−1, TPC: total phe-
nolic content (mg 100 g−1 fresh tuber), Vit-C: vitamin C (mg 100 g−1 fresh tuber).

PC2 explained 19.9% of the total variation, which is mostly dominated by the nega-
tive coefficients of the number of leaves at 115 DAP, vine length at 115 DAP, number of
branches, fresh weight plant−1, tuber length, tuber diameter, tuber weight, SPAD, and vit-
Stresses 2024, 4 889

NB: number of branches, SD: stem diameter (cm), FWP: fresh weight plant−1 (g), TL: tuber length (cm),
TD: tuber diameter (cm), TW: tuber weight (g), NTP: number of tubers plant−1 , TPC: total phenolic
content (mg 100 g−1 fresh tuber), Vit-C: vitamin C (mg 100 g−1 fresh tuber).

PC2 explained 19.9% of the total variation, which is mostly dominated by the negative
coefficients of the number of leaves at 115 DAP, vine length at 115 DAP, number of branches,
fresh weight plant−1 , tuber length, tuber diameter, tuber weight, SPAD, and vitamin C and
Zn content. Both PC2 and PC3 separated treatment T1 from T2 for positive and negative
PC scores, respectively (Figures 5 and S2).

3. Discussion
This study was conducted to analyze the effect of reduced supply of potassium
fertilizer (MoP) dosages on morphological and biochemical properties of sweetpotato.
At harvest, fresh weight plant−1 and tuber number plant−1 obtained the highest value
when the full dosage of K was applied. Increased tuber weight and tuber number plant−1
that ultimately increase the tuber yield are highly dependent on potassium application.
This may be because potassium plays a pivotal role in photosynthesis, promotes a high
energy state, and aids in the crop’s timely and proper nutrient translocation and root water
absorption. As a result, there are more photosynthates available, which allows the plant to
grow more tubers [19].
Potassium is essential for the synthesis of chlorophyll, the green pigment, critical
for photosynthesis. It is vital for the opening and closing of the stomata, which allows
efficient CO2 uptake for photosynthesis. Adequate potassium also boosts the production
of carbohydrates and energy needed for chlorophyll synthesis [20]. Moreover, potassium
activates enzymes essential for photosynthesis, particularly those that produce ATP and
NADPH molecules that fuel photosynthetic reactions and aid in chlorophyll synthesis.
The optimal functioning of these enzymes is critical for chlorophyll content and over-
all photosynthetic efficiency [21]. Furthermore, research shows that potassium reduces
chlorophyll degradation by stabilizing cellular membranes and mitigating oxidative stress.
In potassium-deficient plants, chlorophyll breaks down more readily, causing chlorosis
and reducing photosynthetic efficiency [15]. In the current study, leaf chlorophyll content
(SPAD) was highest when there was the full recommended dose of K fertilizer, indicating
the positive relationship between higher chlorophyll content and an increased amount of
potassium applied [22].
This study showed a different trend for total phenolic content and vitamin C [23]. It
was observed that total phenolic content and vitamin C were the highest when no MoP
was applied. Contrarily, Redovnikovic et al. [24], concluded that adequate potassium
levels can enhance the activity of enzymes responsible for phenolic synthesis, leading to
increased phenolic content in tubers. Furthermore, potassium promotes photosynthesis,
which is essential for the synthesis of vitamin C in plants. Improved photosynthetic activity
can lead to higher vitamin C levels in tubers [20] indicating that reduced potassium may
reduce photosynthetic activity by decreasing overall shoot growth and chlorophyll content
(Figure S1).
Carotenoid and anthocyanin contribute significantly to human health through their
antioxidant, anti-inflammatory, and immune-boosting properties. Regular consumption of
carotenoid and anthocyanin-rich foods can help reduce the risk of chronic diseases and sup-
port overall human well-being [25,26]. Potassium significantly impacts the availability and
synthesis of carotenoids and anthocyanins in tubers by activating key enzymes, enhancing
photosynthesis, and improving plant stress responses. Ensuring adequate potassium levels
is crucial for optimizing the nutritional quality and visual appeal of tubers [27]. In this
experiment, carotenoid and anthocyanin availability were increased with the increase of
K supply. Nevertheless, Ooi et al. [28] found a contradictory result where the amount of
these two pigments decreased with increased potassium. In plants, potassium influences
enzyme activity and other pathways that might reduce the production of these pigments.
Stresses 2024, 4 890

Zinc and Fe are essential trace elements that play critical roles in human health.
Potassium significantly influences the availability and uptake of Zn and Fe in tubers by
enhancing root development, improving soil conditions, and facilitating nutrient transport
and metabolism. Maintaining adequate potassium levels is crucial for optimizing the
nutritional quality of tubers [29]. In this experiment, Zn content was the highest while
the half dosage of K was applied, and Fe content reached the highest value with the full
recommended dosage.
Improving tuber yield involves studying the link between morphological traits and
biochemical markers. By assessing these correlations, researchers can identify key yield-
influencing traits, aiding in targeted breeding for higher-yielding crop varieties. In this
study, anthocyanin was positively correlated with tuber diameter and fresh weight plant−1 .
In some potato varieties, higher anthocyanin content often accompanies greater fresh
weight, as these anthocyanins are concentrated in the skin or flesh of larger, healthier tubers.
Larger tubers tend to accumulate more anthocyanins, particularly in pigmented varieties,
due to increased surface area or flesh volume for pigment synthesis [30]. Furthermore,
carotenoid was positively correlated with stem diameter. In sweetpotatoes, thicker stem
diameters often indicate robust growth, which supports nutrient and water transportation
essential for carotenoid biosynthesis. Carotenoids are synthesized as part of the photo-
synthetic apparatus and are known to increase with plant vigor. A study by Brown [30],
highlights that higher carotenoid concentrations are generally found in well-nourished,
structurally healthy potato plants, which also tend to have thicker stems.
However, vitamin C had a significant negative correlation with the number of tu-
ber plant−1 . This is contradictory with other findings. According to Rosero et al. [31],
environmental stressors such as drought or nutrient deficiencies can impact both tuber
development and vitamin C synthesis. Under stress conditions, plants may produce fewer
tubers and lower vitamin C levels. Conversely, well-managed environments that promote
healthy growth often lead to higher tuber numbers and enhanced vitamin C content.
In addition, the number of branches were negatively correlated with Zn. Studies have
indicated that excessive Zn can adversely affect plant morphology, leading to reduced
branching. High levels of Zn can lead to imbalances in other essential nutrients, inhibiting
branch development [32].
Optimal potassium fertilization enhances sweetpotato yield, tuber quality, and nu-
trient content by supporting photosynthesis, enzyme function, and nutrient uptake. Full
potassium dosage increased the tuber number, fresh weight plant−1 , chlorophyll con-
tent, carotenoid, and anthocyanin, while influencing key nutrients like vitamin C, phe-
nolics, Zn, and Fe. These findings emphasize potassium’s vital role in enhancing sweet-
potato productivity and nutritional quality, providing a foundation for optimized crop
management practices.

4. Materials and Methods

4.1. Site and Soil Characteristics
This experiment was carried out in the agricultural research field of the Interna-
tional University of Business Agriculture and Technology (IUBAT) from October 2023 to
March 2024. The research aimed to examine the effects of different MoP fertilizer dosages
on the growth and yield of sweetpotatoes. The USDA soil taxonomy (USDA 1975) classifies
the soil in this location as a gray terrace. It is in the Madhupur Tract (AEZ-28), an agroe-
cological zone, and part of the Chhiata soil series. The biochemical properties of soil are
given in Table 3.
 productivity and nutritional quality, providing a foundation for optimized crop manage-
ment practices.

Stresses 2024, 4 891

4. Materials and Methods
4.1. Site and Soil Characteristics
Table This experiment
3. Chemical was carried
properties of soil ofout in the agricultural
Madhupur research
tract (Habibur field of the International
et al. 2020).
University of Business Agriculture and Technology (IUBAT) from October 2023 to March
2024. The research aimed to examine the effects of different MoPValues
Parameters fertilizer dosages on the
growth and yield of pH sweetpotatoes. The USDA soil taxonomy (USDA 6.5 1975) classifies the
soil in this location as amatter
Organic gray terrace. It is in the Madhupur Tract (AEZ-28),
1.1% an agroecolog-
N 0.064%
ical zone, and part of the Chhiata soil series. The biochemical properties of soil are given
in Table 3. K 0.13 meq 100 g−1
P −1
13.4 µg g
S 13.3
Table 3. Chemical properties of soil of Madhupur tract (Habibur et al. µg g−1
2020).
Zn 0.73 µg g−1
B
Parameters 0.17 µg g−1
Values
pH 6.5
4.2. Treatments Organic matter 1.1%
The sweetpotato N
variety known as BAU sweetpotato-5 was0.064% taken in this experiment.
As treatments, varyingK dosages of MoP fertilizer were applied. In total, gthere
0.13 meq100 −1 were three
treatments (Table 4). PA randomized complete block design 13.4 (RCBD)
µg g with
−1 four replica-
tions was used in thisS experiment (Figure 6). In this investigation,
13.3 µg gMoP fertilizer was
−1

used as a source of potassium

Zn and applied twice at 30 and 60 days
0.73 after
µg g −1 transplanting.
The 1.0 m × 0.8 m plots
B received manures and fertilizers at the recommendation
0.17 µg g −1 of the
Bangladesh Agricultural Research Institute (BARI).
4.2. Treatments
Table 4. Dosages of MoP fertilizer imposed as three levels of treatments.
The sweetpotato variety known as BAU sweetpotato-5 was taken in this experiment.
As treatments, varying dosages of MoP fertilizer were MoPapplied.
Dosages In total, there were three
Treatment
treatments (Table 4). A randomized complete block design (RCBD) with four−1replications
kg ha− 1 g plot
was used in this
T0
experiment (Figure 6). In this
321.6
investigation, MoP fertilizer
20
was used as a
source of potassium
T1 and applied twice at 30 and
160.8 60 days after transplanting.
10 The 1.0 m x
0.8 m plots received
T2 manures and fertilizers
No at the recommendation ofNothe Bangladesh
Agricultural Research Institute (BARI).

Figure 6.
Figure 6. Experimental
Experimental set
set up
up (a),
(a), tuber
tuber growth
growth under
under T1
T1 (b)
(b) and collected
collected tuber
tuber samples
samples from
from three
three
different treatments
different treatments(c).
(c).

4.3. Planting of Vines

Vines of disease-free and healthy sweetpotato genotype (20–22 cm vine length with
5–6 nodes) were planted in rows on well-prepared soil with 0.6 m × 0.4 m spacings. The
ridge approach was used to generate sweetpotato storage roots and leaves. To improve
productivity, recommended dosages of fertilizers, fungicides, insecticides, and manures
Stresses 2024, 4 892

were applied. During plant growth, techniques such as vine lifting, weeding, irrigation
three times, and earthing up the base of the crops were used. Fourteen days prior to the
storage roots being harvested, the irrigation was stopped.

4.4. Data Collection

A variety of plant-related metrics, responsible for development, yield, and biochemical
qualities were measured. Vine length (cm), number of leaves, number of branches, and
stem diameter (cm) were the traits responsible for development. Data for these traits were
measured from the largest vine at harvest. Traits contributing to yield such as fresh weight
plant−1 (g), tuber length (cm), tuber diameter (cm), tuber weight (g), and number of tubers
plant−1 were recorded at harvest. Furthermore, biochemical properties namely chlorophyll
content (SPAD value), total phenolic content (TPC, mg 100 g−1 fresh tuber), vitamin C
(mg 100 g−1 fresh tuber), carotenoid (mg 100 g−1 fresh tuber), anthocyanin (mg 100 g−1
fresh tuber), glucose, fructose, sucrose, Zn (mg kg−1 ), and Fe (mg kg−1 ) content in tubers
were measured according to the following techniques.

4.5. Determination of Chlorophyll Content

A chlorophyll meter (SPAD-502, Minolta, Tokyo, Japan) was employed to determine
the chlorophyll content of sweetpotato leaves.

4.6. Determination of Total Phenolic and Vitamin C

To determine total phenolics and vitamin C, a fully matured sweetpotato tuber was
collected from each treatment. Total phenol estimation in sweetpotato was carried out
with the Folin−Ciocalteau reagent [33]. The concentration of phenols in sweetpotato was
calculated against the catechol standard curve and expressed as mg phenols/100 g material.
On the other hand, to determine vitamin C content, about 10 g sweetpotato flesh was
ground with 4% oxalic acid. The slurry was filtered, and the filtrate was collected into a
volumetric flask. Then ascorbic acid (AA) content in sweetpotato was estimated based on
the reduction of 2,6-dichlorophenol indophenol dye by visual titration as outlined by [33].
Results of vitamin C content were expressed as milligrams of AA per 100 g of fresh weight.

4.7. Determination of β-Carotene

A one-gram portion of a fresh tuber sample was crushed and meticulously blended
with a 10 mL solution composed of acetone and hexane in a 4:6 ratio. Afterward, the
mixture underwent centrifugation, and the optical density of the resulting supernatant was
measured using a spectrophotometer, specifically UV-160A (Shimadzu Corp., Kyoto, Japan),
at multiple wavelengths, including 663 nm, 645 nm, 505 nm, and 453 nm. Subsequent
calculations were performed using the following formula [34].
β carotene (mg/100 g) = 0.216(OD 663) + 0.452(OD 453) − 1.22 (OD 645) − 0.304 (OD 505)
where OD indicates optical density.

4.8. Estimation of Anthocyanin

For anthocyanin quantification, 100 mg of fresh sweetpotato tuber samples were
homogenized in 3 mL of acidic ethanol (95% ethanol with 1.5 N HCL). The mixture was
incubated at 4 ◦ C for 1 h with gentle agitation, followed by centrifugation at 8000 rpm at
4 ◦ C for 10 min. Absorbance was then measured at 530 and 657 nm wavelengths using a
UV-visible spectrophotometer [35], and the amount of anthocyanin was determined using
the following formula:

QAnthocyanin = (A530 − 0.25 × A 657 ) × M−1

Here, QAnthocyanin = amount of anthocyanin

A530 and A657 = absorptions at the indicated wavelengths
M = weight of the plant materials (mg)
Stresses 2024, 4 893

4.9. Determination of Zn and Fe

To determine the contents of Zn and Fe, collected sweetpotato samples were chopped
into small pieces with a sharp stainless-steel knife and dried for roughly 72 hrs in an electric
oven at a temperature of 50 ◦ C. The samples were then pulverized in a grinding mill and
utilized to make an extract by a wet oxidation technique using a di-acid mixture as outlined
by [36]. Determination of Zn and Fe in aqueous extracts of sweetpotato was carried out
using an atomic absorption spectrophotometer (AAS) (AA-7000, Shimadzu Corp., Japan).
Hollow cathode lamps of Zn and Fe were employed as light sources at wavelengths of
213.9 and 248.3 nm, respectively. All instrumental parameters were adjusted according to
the manufacturer’s instructions.

4.10. Statistical Analysis

Minitab 20 statistical software tools (Minitab Inc., State College, PA, USA) were used
to conduct statistical analysis such as analysis of variance (ANOVA) and principal com-
ponent analysis (PCA). Pearson correlation analysis was executed with R programming
software version 4.4.1. A one-way analysis of variance (ANOVA) was performed for each
morphological and biochemical feature using the general linear model (GLM) as a guide.
As a post hoc study, Tukey’s pairwise comparison was used to identify any significant
changes between treatments.

5. Conclusions
The current study was conducted to determine whether different potassium (K) fer-
tilizer dosages affect tuber and yield-contributing characters. In addition, different bio-
chemical properties were also analyzed to obtain a clear idea about tuber quality. This
study revealed significant variations among treatments for several morphological and
biochemical traits. All the morphological traits excluding the number of leaves at 115 DAP
and tuber length had their highest value when a full dosage of MoP was applied. Among
the biochemical traits, total phenolic, vitamin C, and Zn content reached their highest value
in T2 . In contrast, the rest of the biochemical properties had their highest value with a full
dosage of MoP. Sweetpotato plants typically respond positively to K fertilization, as potas-
sium is essential for their growth, tuber yield, and quality. However, excessive amounts
may lower concentrations of beneficial compounds like carotenoids and anthocyanins.

Supplementary Materials: The following supporting information can be downloaded at: https://www.
mdpi.com/article/10.3390/stresses4040059/s1. Table S1: Mean performance of BAU sweetpotato-5
for morphological traits under three treatments (T0 = 321.8 kg MoP ha−1 , T1 = 160.8 kg MoP ha−1
and T2 = 0.0 kg MoP ha−1 ; Table S2: Mean performance of BAU sweetpotato-5 for biochemical traits
under three treatments (T0 = 321.8 kg MoP ha−1 , T1 = 160.8 kg MoP ha−1 and T2 = 0.0 kg MoP ha−1 );
Figure S1: Variation among three treatments (T0 = 321.8 kg MoP ha−1 , T1 = 160.8 kg MoP ha−1 and
T2 = 0.0 kg MoP ha−1 for leaf chlorophyll content (SPAD value); Figure S2: Scatterplot of PC1 and
PC3 showing differences among treatments.).
Author Contributions: Conceptualization, S.S. and A.H.K.R.; Data curation, S.S., M.N.H.A., A.A.K.
and M.A.S.T.; Formal analysis, A.M.M.M.U.T. and M.Z.H.; Funding acquisition, M.Z.H. and A.H.K.R.;
Investigation, S.S., M.N.H.A., A.A.K. and M.Z.H.; Methodology, S.S., M.N.H.A. and A.A.K.; Super-
vision, M.S.M.; Validation, M.S.M. and A.H.K.R.; Writing—original draft, S.S., A.M.M.M.U.T. and
A.H.K.R.; Writing—review and editing, M.Z.H. and A.H.K.R. All authors have read and agreed to
the published version of the manuscript.
Funding: This research received no external funding.
Data Availability Statement: The data are available upon reasonable request from the authors.
Acknowledgments: The authors would like to express gratitude to the College of Agricultural
Sciences of IUBAT, the Department of Genetics and Plant Breeding and Agricultural Chemistry of
Bangladesh Agricultural University, the Plant Breeding division of the Bangladesh Rice Research
Stresses 2024, 4 894

Institute, Gazipur, and the Department of Horticulture of Sylhet Agricultural University for their
cooperation to conduct and complete the analysis process for manuscript preparation.
Conflicts of Interest: The authors declare no conflicts of interest.

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