The antiviral potential of macroalgae in suppressing Sweet potato leaf curl virus (SPLCV) infection in sweet potatoes

Abstract

Listihani L, Yuniti IGAD, Sapanca PLY, Pandawani NP, Selangga DGW. 2023. The antiviral potential of macroalgae in suppressing Sweet potato leaf curl virus (SPLCV) infection in sweet potatoes. Biodiversitas 24: 4079-4086. Sweet potato leaf curl virus (SPLCV) was first found in sweet potatoes in Indonesia in 2022. Prevention of spread of virus is essential, especially by using macroalgae extract which is environmentally friendly and has antiviral activity. The aim of present research was to test the potential of sea macroalgae to suppress SPLCV infection and to analyze phytochemicals of potential macroalgae containing an antiviral substance. Macroalgae extract was sprayed on the test plants that were infected by SPLCV. The observed parameters were changes in symptoms, disease incidence and severity, virus confirmation by PCR, and phytochemical analysis. The test results up to day 21 showed that Eucheuma spinosum was found to be effective in suppressing SPLCV infection in sweet potatoes, up to symptomless infection in young leaves. E. spinosum and E. cottonii suppressed disease incidence by 80% and 40% and lower disease severity as much as 71% and 48%, while E. serra showed less ability to suppress SPLCV infection. The two macroalgae had flavonoid, saponin, and steroid content which may be the reason to suppress the viral infection. The results of PCR analysis showed that microalgal extract had the highest nucleotide and amino acid homology with Gianyar (LC586170) isolate with values of 99.7 and 100%. The macroalgae with the highest ability to suppress the virus were E. spinosum and E. cottonii. This showed that the application of macroalgae extract did not change the amino acid sequence of SPLCV isolate.

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B I O D I V E R S I T A S
ISSN: 1412-033X
Volume 24, Number 7, July 2023 E-ISSN: 2085-4722
Pages: 4079-4086 DOI: 10.13057/biodiv/d240746
The antiviral potential of macroalgae in suppressing Sweet potato leaf
curl virus (SPLCV) infection in sweet potatoes
LISTIHANI LISTIHANI1,♥, I GUSTI AYU DIAH YUNITI1, PUTU LASMI YULIANTHI SAPANCA1,
NI PUTU PANDAWANI1, DEWA GEDE WIRYANGGA SELANGGA2
1Faculty of Agriculture and Business, Universitas Mahasaraswati Denpasar. Jl. Kamboja No.11A, Dangin Puri Kangin, Kec. Denpasar Utara, Denpasar
80233, Bali, Indonesia. email: listihani9@unmas.ac.id
2Faculty of Agriculture, Universitas Udayana. Jl. Raya Kampus Unud, Jimbaran, Kec. Kuta Sel., Badung 80361, Bali, Indonesia
Manuscript received: 30 January 2023. Revision accepted: 20 July 2023.
Abstract. Listihani L, Yuniti IGAD, Sapanca PLY, Pandawani NP, Selangga DGW. 2023. The antiviral potential of macroalgae in
suppressing Sweet potato leaf curl virus (SPLCV) infection in sweet potatoes. Biodiversitas 24: 4079-4086. Sweet potato leaf curl virus
(SPLCV) was first found in sweet potatoes in Indonesia in 2022. Prevention of spread of virus is essential, especially by using
macroalgae extract which is environmentally friendly and has antiviral activity. The aim of present research was to test the potential of
sea macroalgae to suppress SPLCV infection and to analyze phytochemicals of potential macroalgae containing an antiviral substance.
Macroalgae extract was sprayed on the test plants that were infected by SPLCV. The observed parameters were changes in symptoms,
disease incidence and severity, virus confirmation by PCR, and phytochemical analysis. The test results up to day 21 showed that
Eucheuma spinosum was found to be effective in suppressing SPLCV infection in sweet potatoes, up to symptomless infection in young
leaves. E. spinosum and E. cottonii suppressed disease incidence by 80% and 40% and lower disease severity as much as 71% and 48%,
while E. serra showed less ability to suppress SPLCV infection. The two macroalgae had flavonoid, saponin, and steroid content which
may be the reason to suppress the viral infection. The results of PCR analysis showed that microalgal extract had the highest nucleotide
and amino acid homology with Gianyar (LC586170) isolate with values of 99.7 and 100%. The macroalgae with the highest ability to
suppress the virus were E. spinosum and E. cottonii. This showed that the application of macroalgae extract did not change the amino
acid sequence of SPLCV isolate.
Keywords: Antiviral, Begomovirus, Eucheuma cottonii, Eucheuma serra, Eucheuma spinosum, sweet potato
INTRODUCTION
Sweet potato is one of the staple foods of the people of
Papua, Maluku, East Nusa Tenggara and Bali. Sweet
potatoes were planted in the field by plant cutting. This
method of cultivation allows the virus to be present in the
field during planting into the next generations. More than
20 viruses infect sweet potatoes from the genus
Begomovirus, Carlavirus, Cavemovirus, Crinivirus,
Cucumovirus, Enamovirus, Ipomovirus, Nepovirus,
Potyvirus, Solendovirus, and Tospovirus (Cuellar et al.
2015; Maina et al. 2018). Several important viruses in
sweet potato have been reported, such as sweet potato virus
C (SPVC), sweet potato feathery mottle virus (SPFMV),
sweet potato feathery mottle virus strain internal cork
(SPFMV-IC), sweet potato feathery mottle virus strain
russet crack (SPFMV-RC), sweet potato mild mottle virus
(SPMMV), sweet potato chlorotic stunt virus (SPCSV),
sweet potato virus G (SPVG), and sweet potato leaf curl
virus (SPLCV) (Choi et al. 2012; Clark et al. 2012; Kim et
al. 2015; Maina et al. 2018; Zhang et al. 2020; Listihani
and Selangga 2021; Listihani et al. 2022a). SPLCV
(Geminiviridae; Begomovirus) was first infect sweet
potatoes in Kenya, U.S., China, Japan, Spain, Uganda,
Brazil, Korea, and Tanzania (Albuquerque et al. 2012;
Choi et al. 2012; Cho et al. 2020; Wanjala et al. 2020;
Andreason et al. 2021; Bachwenkizi et al. 2022). The sweet
potato leaf curl virus (SPLCV) has been detected in sweet
potato plants in Badung and Gianyar, Bali (Listihani et al.
2022a). Of a total of 111 plant species in 30 families tested,
SPLCV infection was limited to plants of the
Convolvulaceae family, genus Ipomoea (Ling et al. 2011).
Apart from sweet potato (I. batata), 37 other Ipomoea
species proved to be hosts for SPLCV (Ling et al. 2011).
The natural spread of SPLCV is through vector insects
(Bemisia tabaci) (Andreason et al. 2021). SPLCV causes
an 80% disease incidence in sweet potato crops in Bella
Vista, Corrientes province (NEA) (Pardina et al. 2012).
Large insect vector populations are often found in the field,
allowing the virus to spread more rapidly from one location
to another and making control efforts more difficult. The
plant virus maintenance performed until now involved the
use of pesticides to tackle pests and virus insect vectors in
plants, with the side effect being pathogen resistance
against pesticides and over-accumulation of pesticide
residue on the ground. Environmentally friendly SPLCV
control is essential so that there is no resistance among
pathogens and insect vectors. Natural products like
macroalgae are often considered safe for the environment
for being highly biodegradable and having a low biocidal
activity (Wan et al. 2018). Macroalgae is thought to be a
suitable resource of bioactive components with biological

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activity, such as antibacterial, antifungal, and antiviral
(Hamed et al. 2018).
Sea macroalgae can potentially be used for plant
protection and development. The bioactive components,
such as oil, protein (amino acid), bioflavonoid,
polysaccharide, carotenoid, polyphenol, and carbohydrates
are regarded to have bactericidal, antiviral, antinematode,
and fungicide effects on plant pathogens (Hamed et al.
2018). The macroalgae extract is also used in agriculture as
soil conditioner to improve plant productivity (González et
al. 2013; Lola-Luz et al. 2014; Garcia-Gonzalez and
Sommerfeld 2016; Seif et al. 2016; Thanaa et al. 2016;
Barone et al. 2018; Murata et al. 2021; Ammar et al. 2022).
The polysaccharide content in macroalgae has been
reported to enhanced plant growth, with the ability to
suppress fungi, bacteria and viruses, as well as to improve
productivity in many plants (Sharma et al. 2014). Phenolic
acid and flavonoid bioactive components in the methanol
extract of Sargassum vulgare can act as an antifungal against
Pythium aphanidermatum by inhibiting the pathogenic mycelium
growth by around 51% and lowering disease severity by
82% (Nawaim et al. 2017; Nawaim et al. 2018). Brown
algae Sargassum swartzii controls the rice sheath blight
caused by Rhizoctonia solani. This defense mechanism is
thought to be correlated with high phenolate and the early
accumulation of phytoalexin compound in rice plants (Raj
et al. 2016). Kappa/beta carrageenan extracted from
Tichocarpus crinitus suppressed the TMV infection in
tobacco leaves (Shukla et al. 2016; Asimakis et al. 2022).
Control of viral diseases on cultivated plants technically
using plant barriers and biologically with chitosan, plant
extract, and nonpathogenic bacteria has been studied
previously (Selangga et al. 2018; Triwidodo and Listihani
2020; Pandawani et al. 2022). However, the potential and
use of macroalgae in plant protection to control plant virus
have not been studied. Thus, the aim of present research
was to test the potential of sea macroalgae in suppressing
SPLCV infection and to analyze the phytochemicals of
potential macroalgae containing an antiviral substance.
MATERIALS AND METHODS
Inoculum multiplication
SPLCV virus source plant was obtained from previous
collections of SPLCV-Tegallalang isolates from Gianyar
Regency (Listihani et al. 2022a). The inoculum source was
multiplied on sweet potato plants in different pots to get as
much virus inoculum stock. The test plants used were
sweet potato plants which had been tested by PCR and
showed negative and positive results for SPLCV.
Test plant planting
Sweet potato cutting plants for SPLCV were planted by
using 30 cm x 30 cm siz polybags with 6 kg planting
medium. The plant medium used was manure and dirt with
1:1 ratio. The cutting plants were cut every three joints and
planted on the polybag in the morning, with the
requirements of one joint inside the planting medium and
one leaf left attached. The planted stick was then watered
to maintain the medium’s humidity. Watering was
performed once a day.
Sampling and macroalgae extract production
Macroalgae samples were collected from Serangan
Island. Macroalgae samples were collected by pulling off
the thallus and then washed with water and stored in
strapped plastic containing sterile seawater. The extract of
macroalgae was made from 2 g wet weight of each sample
being grind in liquid nitrogen by using mortar and pestle.
The grounded macroalgae were then diluted three times
with 30 mL methanol and filtered by using Whatman
No.41 filter paper (Santosa 2017). The extract was placed
in a rotary evaporator to separate the methanol and
microalgae extract.
Macroalgae extract application to test plant
The crude extract of macroalgae was diluted in 5% 2-
methoxyethanol to obtain liquid extract with a
concentration of 10 mg.ml-¹ (Santosa 2017). The
macroalgae extract was then sprayed three times on the
leaves of test plant using a mini sprayer. Treated plants
were maintained and observed until light symptoms or
symptomless conditions appeared from severe symptoms.
The present research consisted of one factor and ten
repetitions in the same test environment. The factor was
comprised of three macroalgae extract treatments
(Eucheuma spinosum, Eucheuma cottonii, and Eucheuma
serra) applied on the test plants. Positive control (plants
positive for SPLCV without treatment) and negative
control (plants negative for SPLCV without treatment)
were also used for the research. The variables observed
were symptoms, disease incidence, and severity according
to the score in Table 1.
SPLCV confirmation by PCR and sequencing analysis
The virus detection method by PCR consisted of several
stages: total DNA extraction, DNA amplification, and
amplification product visualization. Total DNA extraction
was done manually through the CTAB method (Doyle and
Doyle 1990). The virus DNA amplification was performed
by using universal primer pair for Begomovirus (SPG2-_5’-
ATCCVAAYWTYCAGGGAGCTAA-3’/SPG1_5’-
CCCKGTGCGWRAATCCAT-3’). The nucleotide and
amino acid homology analysis for DNA virus was
performed by BLAST software in NCBi site
(www.ncbi.nlm.nih.gov). The nucleotide sequences of all
chosen isolates were modified by Bioedit V7.0.5 software
before being used for phylogenetic analysis. The
phylogenetic tree was made by ClustalW software (Bioedit
V7.0.5).
Table 1. Disease score based on visual symptoms in plant
Scores
Symptoms
0
Symptomless
1
Mild vein clearing
2
Mild vein clearing and malformation leaves
3
Severe vein clearing
4
Severe vein clearing and malformation leaves

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Phytochemical analysis
The macroalgae samples showing the effects of SPLCV
infection were used for phytochemical analysis. Microalgae
samples tested for alkaloid, flavonoid, triterpenoid, steroid,
tannin, saponin, carotenoid, and coumarin (Santosa 2017).
RESULTS AND DISCUSSION
SPLCV infection influences the symptoms in sweet
potato leaves (Figure 1). In general, viral infection
symptoms on the leaves are yellowing and curling, while
fruits showed abnormalities in size, color, texture, ripeness,
number of seedlings, and total productivity, and several
viruses cause fruit death (Listihani et al. 2019, 2020,
2022b; Selangga and Listihani 2022; Selangga et al. 2022).
As stated by Listihani et al. (2022a), SPLCV infection
symptoms in young leaves are changes in leaf color into
vein clearing. Based on the test result up to day 21, it was
observed that Eucheuma spinosum showed the best
performance in suppressing SPLCV infection in sweet
potato plants into symptomless disease in young leaves
(Table 2, Figure 2). E. spinosum reduced disease incidence
by 80%, and disease severity by 71%. Reduction in the
content of chlorophyll a, chlorophyll b, carotenoid,
carbohydrate, protein, and amino acids in infected plant is
caused by viral activity, causing symptoms to appear on the
plants (Soni et al. 2022). The difference in the content level
decrease in plants causes different disease severity scores
(Ghannam et al. 2013; Ahmadi et al. 2015). In the present
study, several macroalgae extract treatments, such as
Eucheuma cottonii and Eucheuma serra were able to
suppress SPLCV disease incidence by up to 40% with mild
vein-clearing symptoms and by 10% with severe vein-
clearing symptoms. In comparison, positive control plants
showed disease incidence of 100% with severe vein-
clearing symptoms. Disease severity in positive control
plants continued to increase with growing time, ranging
from 85% from 78%. In contrast, plants given macroalgae
extract showed a trend of decreasing disease incidence and
severity along with growing time. Viral infection in sweet
potato leaves was suppressed after treatment with extracts,
causing previously severe symptoms to be mild or
asymptomatic. All three macroalgae types were able to
suppress viral infection.
A recovery period occurs when plants infected with the
virus show very severe symptoms, but over a period of
time the symptoms disappear or change into mild
symptoms, especially on freshly grown plant parts
(Listihani et al. 2021; Selangga et al. 2021; Selangga et al.
2023). The inhibition level of SPLCV infection ranged
between 5-71%, which was shown by macroalgae extract
treatment (Table 2). The level of inhibition between three
treatments may be influenced by certain inhibitory
mechanisms activated by the application of the extract
used. A similar result was also reported by Santosa (2017)
who stated that macroalgae extract treatment can lower the
disease incidence and severity when compared to CMV
infected control plants without treatment.
Figure 1. Vein clearing symptoms on sweetpotato leaves before macroalgae treatment: A. negative control; B. positive control; C. E.
spinosum treatment; D. E. cottonii treatment; and E. E. serra treatment
Figure 2. Vein clearing symptoms on sweetpotato leaves after macroalgae treatment: A. negative control; B. positive control; C. E.
spinosum treatment; D. E. cottonii treatment; and E. E. serra treatment
A
B
C
D
E
A
B
C
D
E

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Macroalgae extract treatment on SPLCV showed
different results for each type, macroalgae extract treatment
showed significantly different symptoms changes
compared to leaves without any treatment (positive control)
(Figures 1 and 2). According to Pandawani et al. (2022),
extract treatment that has been inoculated by virus did not
show symptoms because biological control can suppress
infection and virus multiplication as well as inhibit
replication and spread inside the plant. It has been observed
that macroalgae extract could suppress virus from
multiplying inside the plants so that no symptom appeared
on the leaf surface. It was recorded that plants that were
given the extract treatment showed varied symptoms from
day 14 to day 21, while control leaf symptoms showed
increasingly severe symptoms on young leaves. Plants in
negative control (without extract treatment) appeared
without symptom, and the PCR result showed a negative
result for Begomovirus. Although symptom changes were
found on plants given the extract treatments, the PCR result
showed them to be positive for Begomovirus. This was
because virus particles were present on the leaves in small
numbers or inactive, causing no symptoms but could be
detected by PCR. SPLCV isolates that were given
macroalgae extract treatment were analyzed for molecular
content by PCR. Results revealed that nucleotide and
amino acid homology was found to be highest with SPLCV
isolates from Gianyar (LC586170) with the value of 99.7
and 100% (Table 3). The phylogenetic tree analysis also
showed that SPLCV that was given extract treatment
showed the same group with Gianyar isolates and was
different from other isolate groups available in the
GenBank (Figure 3). This showed that macroalgae extract
application causes several nucleotide base sequence
changes but did not change the amino acid sequence of
SPLCV isolate.
Table 2. The effect of macroalgae application on disease symptoms and severity of vein clearing in sweetpotato plants
Treatments
Before treatment
Four weeks after treatment
Begomovirus
detection by
PCR
Disease symptoms
Disease
incidence (%)
Disease
severity
(%)
Disease symptoms
Disease
incidence (%)
Disease
severity
(%)
C-
Symptomless
0 (0/10)
0
Symptomless
0 (0/10)
0
-
C+
Severe vein clearing
100 (10/10)
78
Severe vein clearing
and malformation
leaves
100 (10/10)
85
+
Eucheuma
spinosum
Severe vein clearing
100 (10/10)
78
Symptomless and
Mild vein clearing
20 (2/10)
7
+
Eucheuma cottonii
Severe vein clearing
100 (10/10)
79
Mild vein clearing
60 (6/10)
31
+
Eucheuma serra
Severe vein clearing
100 (10/10)
77
Severe vein clearing
90 (9/10)
72
+
Note: negative control, C- (SPLCV negative test plants without treatment); positive control, C+ (SPLCV positive test plants without
treatment)
Table 3. Homology of nucleotide and amino acid of SPLCV isolates after treatment with SPLCV isolates from Gianyar
Isolates
Geographical origin
Hosts
Symptoms
Homology (%)
Accession
numbers
SPLCV after
treatment
nt
aa
U Ubud-Ubud-1
Gianyar, Indonesia
Ipomoea batatas
Vein clearing
99.7
100
LC586170
hu194 Hu-194
Hunan, China
Ipomoea batatas
Vein clearing
97.7
98.8
MK052985
ZJ
Zhejiang, China
Ipomoea setosa
Leaf curling
96.5
97.4
JF736657
202
South Korea
Ipomoea batatas
Leaf curling
96.1
97.1
KT992065
169
South Korea
Ipomoea batatas
Leaf curling
96.4
97.6
KT992062
GE-21
Muan, South Korea
Ipomoea batatas
Unknown
96.0
97.1
JX961673
7
South Korea
Ipomoea batatas
Leaf curling
95.7
96.9
KT992048
Sp3-2
Spain
Unknown
Unknown
89.0
90.9
KT099145
P213-11
Southern Portugal
Ipomoea indica
Vein clearing
88.6
90.2
MG254543
P213-8
Southern Portugal
Ipomoea indica
Vein clearing
88.3
90.0
MG254542
409
Khartoum, Sudan
Ipomoea batatas
Lef curling
88.8
90.4
KY270782
Uk-2008
Kampala, Uganda
Ipomoea setosa
Leaf curling
88.8
90.4
FR751068
648B-9
South Carolina, USA
Ipomoea batatas
Leaf curling
88.2
90.0
HQ333144
BR-Uti-08
Bahia, Brazil
Ipomoea batatas
Leaf curling
88.2
90.0
HQ393447
WS1-4
South Carolina, USA
Ipomoea setosa
Leaf curling
88.5
90.2
HQ333141
MP3-09
Pernambuco, Brazil
Ipomoea batatas
Leaf curling
87.8
89.7
HQ393470
*TYLCV
Masan, South Korea
Lycopersicon esculentum
Leaf curling
66.5
69.6
HM130912
Note: *TYLCV: Tomato yellows leaf curl virus as out group; nt (nucleotide) and aa (amino acid)

LISTIHANI et al. – The antiviral potential of macroalgae in suppressing SPLCV infection in sweet potatoes
4083
Figure 3. Phylogenetic tree of AC1 and AC2 SPLCV genes for Bali isolates based on the SPLCV nucleotide sequence using Tomato
yellows leaf curl virus (TYLCV) as the out group. IDN-Indonesia
Table 4. Phytochemical analysis of selected macroalgae species
Species
Alkaloid
Flavonoid
Saponin
Steroid
Eucheuma spinosum
-
+
++
+++
Eucheuma cottonii
-
++
++
++
Note: -: Absent, +: Little content, ++: Medium content, +++: High content
The phytochemical analysis was only tested on two of
three macroalgae species, which were E. spinosum and E.
cottonii. E. spinosum and E. cottonii. The species were
chosen to show their ability to suppress SPLCV moderately
(E. cottonii) and highly (E. spinosum). The phytochemical
analysis showed that E. spinosum and E. cottonii. did not
contain alkaloids, but both contained steroids in different
amounts (Table 4). E. spinosum species contained high
steroid content, but E. cottonii species had low steroid
content. Both species showed negative results for tannin,
quinone or even triterpenoid contents, but saponin content
was found in E. spinosum and E. cottonii. Flavonoid
content was found in both species, but highest content was
found in E. cottonii.
Extract application in suppressing viral infection
enhances several enzyme activities, such as peroxidase,
polyphenol oxidase, and phenol (Abdelkhalek et al. 2021).
Healthy plants contain a lot of highly soluble proteins that
are the components of virus coat protein synthesis (Martins
et al. 2022). The induction of macroalgae extract in the
plants can lower the level of soluble protein, making the
environment less advantageous for virus replication.
Macroalgae and plants have the ability to produce
bioactive substances that can suppress pathogens.
Flavonoid has a role in plant protection against biotic factor
(herbivores, pathogen) and abiotic pressure (UV radiation,
heat) (Mierziak et al. 2014). Flavonoid also tightens plant
and tissue structures by controlling the auxin activity (IAA)
which prevents pathogen infection and is related to
pathogenic enzyme inhibition, especially those that damage
plant cell wall (Mierziak et al. 2014).
Based on the research result, test plants given
macroalgae extract after being inoculated by SPLCV
changed their symptom to mild and symptomless. They
KY270782_Sudan
HQ333141_USA
HQ393470_Brazil
HQ333144_USA
FR751068_Uganda
HQ393447_Brazil
KT099145_Spain
MG254543_Portugal
MG254542_Portugal
SPLCV after treatment
LC586170_IDN_Gianyar
JF736657_China
MK052985_China
JX961673_SouthKorea
KT992062_SouthKorea
KT992065_SouthKorea
KT992048_SouthKorea
HM130912_TYLCV
100
75
89
86
95
90
95
83
95
94
89
84
82
76
77
0.05
I
II

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also showed lower disease incidence and severity
compared to untreated test plants. This is because
compounds trigger salicylic acid inside the plant, which
induces plant’s defense against virus (Sharma et al. 2014;
Sudirman et al. 2018). Thus, it improves the plant
resistance and allows it to endure virus attach. The
mechanism of macroalgae antiviral interaction is explained
as the inhibition of virus adsorption into the host cell, after
passing the competition with attaching virus or through a
synergic combination between polysaccharides and the
host. The mechanism is that polysaccharide blocks the cell
host, so the virus cannot get in and infect (Hamed et al.
2018). Macroalgae mechanism in inhibiting plant virus
replication has previously been reported. Zhao et al. (2017)
reported that macroalgae inhibit the replication of Potato
virus X (PVX) up to 95% in potatoes. Zhao et al. (2015)
and Stadnik and De Freitas (2014) also reported that
Dictyota spp. has antiviral activity against plant viruses for
containing of polysaccharides. A study from Santosa
(2017) also showed that Dictyota cervicornis has antiviral
potential as it can supressed the number of local lesions on
C. amaranticolor infected by CMV for up to 96.25%; the
possible use of D. cervicornis as antiviral is also due to the
high level of polysaccharides in it. Sami et al. (2021)
reported that E. spinosum and E. cottonii has high
polysaccharide content which makes them great for use as
antiviral. E. cottonii contain various nutrition, such as
protein, lipid, carbohydrate, and bioactive compounds
(Biris-Dorhoi et al. 2020; Hentati et al. 2020; Martins et al.
2022). The bioactive compounds present in various algae
are polyphenol (Hentati et al. 2020), alkaloid, terpen,
pigment, sterole, fatty acid (Barbosa et al. 2014),
carrageenan, fucan, and several other compounds that have
been proven to potentially be used as antiviral,
antibacterial, and anticancer (Kalitnik et al. 2013; Prajapati
et al. 2014). Eucheuma spinosum and Eucheuma cottonii
contain carrageenan which is proven to act as an antiviral.
Carrageenan’s mechanism as an antivirus is by inactivating
viral particles so that virus cannot replicate (Sangha et al.
2015). Eucheuma cottonii is a type of red algae that can
produce polysaccharides such as carrageenan (Sudirman et
al. 2018; Lomartire et al. 2022). The polysaccharide
content in Eucheuma cottonii is crucial for all organisms
and has various biological functions, including as anti-
inflammatory agent, anticoagulant, antibacterial,
antioxidant activity, and inhibit virus attack (Hentati et al.
2020; Carpena et al. 2022). The faster the plant symptom
turning into mild indicates that the extract application can
inhibit damages due to viral activity in plants. Suppression
of symptoms probably occur due to salicylic acid function
as an indirect inhibitor of virus systemic movement through
the host vascular tissue, resulting in symptoms delay
(Ghannam et al. 2013). The given macroalgae extract
showed its activity on virus-infected plant as a virus
inhibitor. Viral inhibitor is a compound that can prevent
viral infection which is present in the sap of certain plants
(Duarte et al. 2021).
Several compounds are produced by plants as pathogen
inhibitors are flavanoid, chitinase, phytoalexin, peroxidase,
polyphenol oxidase, and lipoxidase (Duarte et al. 2021).
Improving plant defense against pathogen infection can be
done by inducing systemic defense in the plant itself
(Selangga et al. 2018). Systemic defense induction by
induction agent (Systemic Acquired Resistance/SAR) is a
method that has been developed to produce plants that are
more resistant to disease. The flavonoid and steroid
compounds in macroalgae extract act as systemic defense
inducing agent which activates the plant defense system
and thus improves the plant defense mechanism against
virus. Phenolic compounds, and flavonoids are known to be
important as a signal molecule in several plant defense
responses. The expression of SAR is very dependent on the
accumulation of flavonoids or salicylic acid and associated
with pathogenesis-related protein (PR protein) which has
anti-pathogen activity (Zhou et al. 2021).
Conclusions
Macroalgae extract treatment showed that treated sweet
potato had lower disease incidence and severe and mild
symptoms or even symptomless, compared to positive
control plants that were only infected by virus. E. spinosum
and E. cottonii were very effective in controlling SPLCV
infection in sweet potatoes. Phytochemicals like, steroid
and flavonoid may be play an important role to suppress
viral infection in plants.
ACKNOWLEDGEMENTS
This research was funded by Universitas Mahasaraswati
Denpasar for Listihani and team through superior basic
research of Unmas Denpasar Scheme with contract no.
K.116/B.0101/LPPM-Unmas/V/2022.
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