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Agricultural Sciences, 2019, 10, 1104-1112
http://www.scirp.org/journal/as
ISSN Online: 2156-8561
ISSN Print: 2156-8553
DOI:
10.4236/as.2019.108083 Aug. 28, 2019 1104 Agricultural Sciences
First Report of Stemphylium vesicarium Causing
Onion Stemphylium Leaf Blight in Ethiopia
Yitayih Gedefaw*, Abebe Gezahegn, Abiy Fekadu, Zeraye Mehari
Department of Plant Pathology, Ethiopian Institute of Agricultural Research (EIAR), Melkassa Agricultural Research Center (MARC),
Adama, Ethiopia
Abstract
A suspected fungal disease was observed on onion leaves during survey
in
onion fields of the central rift valley of Ethiopia in the offseason in
2019. The
disease symptoms were round to oval small spots on onion leaves which coa-
lesce to form blighted leaves that change to brown lesion and black sporula-
tion with time. The disease was of high incidence (up to 95.2%) and severity
(up to 4.67) where in some fields it has been causing early plant senesce
nce
and reduced bulb size during harvest with massive yield loss, named
to be
“Yeshinkurt Ebola” to mean “Ebola of onion
” by farmers. Dirty white to light
grey front colony color and light brown to deep brown reverse colony color
with alternative white and brown band fungal growth were isolated from in-
fected onion leaf samples. The conidia were olive brown, oval to ovoid, ob-
long and ovoid to oblong are born on conidiophores. Pathogenicity of the
pathogen was confirmed on 45-days-old onion (cv. Nafis) plant,
and it was
identified as
Stemphylium vesicarium
based on cultural, morphological and
pathogenic results. This is the first report of
S
.
vesicarium
, the causative agent
of onion stemphylium leaf blight.
Keywords
Stemphylium vesicarium
,
Onion, Prevalence, Severity, Pathogenicity
1. Introduction
Many small- and large-scale farmers in the main onion-producing areas of
central rift valley of Ethiopia grow onion (
Allium cepa
L.). In total, 31,673 ha of
land were covered by onion with 293,887.6 tonnes of production, CSA [1].
Nowadays, the area under onion production is increasing. However, its produc-
tion and/or productivity is affected by many biotic (diseases, and insects pests)
and abiotic like imbalanced fertilizer, uneven irrigation and inappropriate agro-
How to cite this paper:
Gedefaw, Y., Ge-
zahegn, A., Fekadu, A. and Mehari, Z.
(201
9) First Report of
Stemphylium vesic
a-
rium
Causing Onion Stemphylium Leaf
Blight in Ethiopia
.
Agricultural Sciences
,
10
, 1104-1112.
https://doi.org/10.4236/as.2019.108083
Received:
July 5, 2019
Accepted:
August 25, 2019
Published:
August 28, 2019
Copyright © 201
9 by author(s) and
Scientific
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access
Y. Gedefaw et al.
DOI:
10.4236/as.2019.108083 1105 Agricultural Sciences
nomic practices, Amin
et al
. [2]. Currently, a strange disease, expected to be
stemphylium leaf blight is observed in farmers’ field and research stations of the
CRV.
Stemphylium leaf blight caused by
Stemphylium vesicarium
Wallr (Simmons)
(teleomorph:
Pleospora allii
. (Rabenh.) Ces. and De Not) is
one of the most de-
structive fungal diseases in
Allium
species. The host range of the pathogen varies
among different crops such as garlic, Suheri and Price [3], chilli pepper, Vitale
et
al
. [4], leek, Suheri and Price [3], asparagus, Foster [5], pear, Llorente and Mon-
tesinos [6] and Köhl
et al
. [7].
Stemphylium leaf blight was first identified from India in 1975 on garlic, Rao
and Pavgi [8] and has subsequently been recorded in USA, Shishkoff and Lor-
beer [9], South Africa, Aveling and Naude [10]; Aveling and Snyman [11], Spain,
Basallote
et al
.
[12], Brazil, Boiteux
et al
. [13] and Turkey, Polat
et al
. [14]. The
genus
Stemphylium
comprises 28 phylogenetically distinguished plant patho-
genic species, Woudenberg
et al
. [15]. Recently, Brahamanage
et al
. [16] re-
viewed the existence of the genus
Stemphylium
in the Netherlands, Bangladesh,
Egypt, Nepal, Syria, and China on different host plants.
Stemphylium vesicarium
is considered as very disruptive disease, which can cause up to 90% yield losses
on onion, Miller
et al
. [17]; Tomaz and Lima [18]; Lorbeer [19], 60 - 90% yield
loss on pear, Llorente and Montesinos [20], and complete spears loss on aspara-
gus, Hausbeck
et al
. [21].
In Ethiopia, purple blotch (
Alternaria porri
) and downy mildew (
Peronospora
destructor
) diseases are considered as the major constraints of onion production
and productivity, Wondirad
et al
. [22]. Purple blotch is prevalent in all onion-
growing areas of the country. It attacks leaves, bulb and seed stalks and subse-
quently reduces yield and quality. Since 2018, however, a new disease symptom,
which confuses with purple blotch disease, was observed in the central rift valley
areas of Ethiopia. The disease typically attacks leaf, which starts with round to
oval small spots that later coalesce to form blighting to leaf tissue. The lesion
turns brown to tan, for some time; the disease was probably misdiagnosed as
purple blotch since their symptoms are very similar. Samples submitted to the
plant pathology laboratory of Melkassa Agricultural Research Center of Ethio-
pian Institute of Agricultural Research (EIAR) revealed the presence of stem-
phylium leaf blight (SLB).
Following the detection of the pathogen (
S
.
vesicarium
) survey was conducted
to have a clear picture of its prevalence, incidence and severity. The survey cov-
ered the main onion producing areas in the central rift valley (CRV) of Ethiopia.
Cultural and morphological characteristics of symptomatic onion leaf samples of
the survey indicated the existence SLB disease (
S
.
vesicarium
).
2. Materials and Methods
2.1. Description of the Study Area
The field survey was conducted during the 2019 cropping season. The survey
Y. Gedefaw et al.
DOI:
10.4236/as.2019.108083 1106 Agricultural Sciences
encompassed a total of 26 onion fields in the five districts (Adama, Bora, Dugda,
Jeju and Lumie) of the CRV (located 08˚00'10.6'' to 08˚30'01.7'' N, 038˚43'53.9''
to 039˚35'21.8'' E) of Ethiopia (Table 1). Characteristic features of surveyed
onion fields were summarized in Table 2.
2.2. Sampling and Sampling Units
Fields were ordinarily selected at intervals of 5 - 10 km along the main roads.
When necessary, the sample sizes (the number of observed fields per district)
and the distance between sample units (the arbitrarily selected quadrants, 5 - 10)
per field were adjusted to suit crop distribution and field-size. All sampled fields
Table 1. Descriptions of surveyed onion fields and associated disease pressure in the Central Rift Valley of Ethiopia (Jan. 14-18,
2019).
ID District Locality Var. Alt (masl) Latitude (N) Longitude (E) DAT DI DS YFFO
1 Jeju HD BR 1258 08˚30'01.7'' 039˚34'24.1'' 75 87.5 4 2017
2 Jeju HD BR 1267 08˚29'49.1'' 039˚34'30.1'' 90 75 3 2017
3 Jeju HD BR 1256 08˚29'45.6'' 039˚34'20.1'' 67 72.5 3 2017
4 Jeju HD BR 1253 08˚29ꞌ 49.5'' 039˚34'22.5ꞌꞌ 60 72.5 2 NI
5 Jeju HD BR 1270 08˚29'32.1'' 039° 35'21.8'' 90 95.2 4 2018
6 Jeju HD BR 1268 08˚29̍̍̍̍̍'34.7'' 039˚35'19.9'' 70 75 4 2018
7 Adama Ml BR 1477 08˚24'10.8'' 039˚21'42.8'' 51 10 2 2017
8 Lumie Koka BR 1598 08˚27'19.7'' 039˚01'39.7ꞌꞌ 60 93 2 2017
9 Lumie Koka BR 1601 08˚27'14.4'' 039˚01'33.8'' 45 40.8 2.33 NI
10 Lumie Koka BR 1595 08˚27'08.9'' 039° 01'29.4'' 60 72.7 2.75 2016
11 Lumie Koka BR 1591 08° 27ꞌ 01.9'' 039˚01'26.7'' 70 94.7 3 2017
12 Lumie Koka BR 1607 08˚21ꞌ 51.2'' 038˚59'51.2'' 70 36.4 2.33 2017
13 Lumie Koka BR 1598 08˚21'36.0'' 038˚59'55.8'' 90 46.7 2.33 2017
14 Bora Kenteri BR 1604 08˚20'33.5'' 038˚59''14.6'' 67 28.37 2.33 NI
15 Bora Kenteri BR 1601 08° 20ꞌ 02.6'' 038˚58'56.1'' 70 20.01 2 NI
16 Bora Elen BR 1654 08˚20'05.4'' 038˚56''31.4ꞌꞌ 35 32.47 2 NI
17 Bora Elen BR 1599 08˚20' 27.8ꞌꞌ 038˚56'22.6'' 66 23.27 2.33 2016
18 Dugda KA BR 1627 08˚06'47.5'' 038˚ 47'45.2'' 30 20.75 2 NI
19 Dugda KA BR 1629 08° 06'47.7'' 038˚47'36.9'' 90 87.18 4.33 NI
20 Dugda KA BR 1651 08˚06'43.5'' 038˚47'12.3'' 90 89.14 4.67 2018
21 Dugda Abono BR 1666 08˚04'30.7'' 038˚45'03.9'' 33 33.7 2 NI
22 Dugda EC BR 1633 08˚00'22.1'' 038˚43'54.9'' 60 50.18 3 2018
23 Dugda EC BR 1626 08˚00'10.6'' 038˚43'53.9'' 90 41.67 3.33 2018
24 Dugda Alemtena BR 1608 08˚19'4.6'' 038˚58'8.6'' 90 22.42 2.33 2018
25 Adama Ml BR 1542 08˚24ꞌ36.7'' 039˚19'32.5'' 70 82.5 3 NI
26 Adama Ml Nafis 1534 08˚24'23.6'' 039˚19'56.6'' 80 82.5 3 NI
Where, Var: variety; Alt: altitude; DAT: days after transplanting (days); DI: disease incidence; DS: disease severity; HD: Horota Dore; Ml: Melkassa; KA:
Korki Adi; EC: Elka Chelemo; BR:Bombe red; NI: no idea and YFFO: year of farmers first observation.
Y. Gedefaw et al.
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10.4236/as.2019.108083 1107 Agricultural Sciences
Table 2. Characteristic features of surveyed onion fields in the Central Rift Valley, Ethi-
opia.
District Altitude (m.a.s.l)
Temperature
range (˚C)
Relative Humidity
range (%)
Cropping
system
a
Dugda 1608.5 - 1666 20.55 - 31.75 37.55 - 73.25 sole
Bora 1599 - 1654 28.90 - 38.90 33.10 - 60.25 sole
Lumie 1591 - 1607 26.70 - 34.40 28.95 - 46.30 sole
Adama 1477 - 1542 24.10 - 29.85 31.50 - 58.30 sole
Jeju 1253 - 1270 30.10 - 31.35 33.20 - 33.50 sole
aOnly dominant cropping systems are indicated. A.Chu.-Ada Chukallaa; AJTSC-African Juice Tibila Share
Company.
belonged to small, private farmers. Each field was visited once. Sampled plants
were randomly selected by using a quadrant (0.5 × 0.5 m) dropped on specified
number of equally spaced paces following an inverted “X” pattern. Having made
the pre-set number of quadrants (according to the size of the field), 3 - 5
plants/quadrant showing the suspected disease symptoms, as shown in Figure 1,
were sampled.
2.3. Diseases Assessment
Disease incidence was assessed by counting the total number of plants having
SLB symptoms divided by the total plant population within the quadrant and
expressed in percentage. Disease severity was determined by a 0 - 5 visual scale
(where: 0: no disease; 1: minute pinhead size spots, 1 - 10% diseased leaf area; 2:
11 - 20% diseased; 3: 21 - 40% diseased; 4: breaking of leaves from center, 41 -
75% diseased leaf area; 5: coalescing lesions with >75% diseased area), Sharma
[23].
2.4. Isolation and Pathogenicity Test of the Pathogen
Small pieces of tissue (5 - 10 cm) containing lesions were incubated in moist
chambers under light for 4 days at 25˚C ± 2˚C to induce sporulation and con-
firm colonization by
S
.
vesicarium
. After 4 days of incubation, conidial and my-
celial masses were purified on to potato dextrose agar (PDA) and incubated for
10 - 16 days at 25˚C ± 2˚C. Cultural, morphological and pathogenicity test were
used for identification.
Virulence test of the isolates recovered was carried out on Nafis onion variety.
Pure culture of 14-days-old
S
.
vesicarium
was flooded with sterile tap water and,
after gently rubbing with a rubber spatula, the resulting suspensions were fil-
tered through sterile nylon gauze. Concentrations of the conidial suspensions
were determined with a haemocytometer, adjusted to 3 × 104 conidia mL−1, Köhl
et al
. [7] with sterile tap water to inoculate 45 days old seedling in the green-
house. The inoculated onion plants were kept up to 45 days in pots in the
greenhouse at 27˚C average temprature and 75% average relative humidity.
Y. Gedefaw et al.
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10.4236/as.2019.108083 1108 Agricultural Sciences
Figure 1. Onion field affected by stemphylium leaf blight: (a) early leaf death and (b) re-
duced bulb size.
3. Results and Discussion
3.1. Symptoms
During the survey, the overall look of onion fields affected by the disease is de-
picted in Figure 1. Early senescence of leaves and flower stalks was observed,
especially, when the severity of the disease was high (Figure 1(a)). Besides, re-
duced bulb size (Figure 1(b)) and associated yield loss was observed whenever
matured onion fields were encountered during the survey. This was further con-
firmed from the communication made with producers during the assessment.
Due to this massive appearance of the disease symptoms and maximum produc-
tion loss, we were even told that farmers in the area call it as “
Yeshinkurt Ebola
”,
meaning “Ebola of onion”. Specific disease symptoms of small to advanced tan
to brown, water-soaked lesions on leaves and onion stalks, advancing to
dark-brown to black sporulation and whitish fruiting structure were common
(Figures 2(a)-(d)). These symptoms were more obvious on older plants. Over-
all, the symptoms observed during the survey are similar with symptoms de-
scription of SLB by Basallote-Ureba
et al
. [24].
3.2. Disease Incidence and Severity
Severity and incidence of SLB in the surveyed area are summarized in Table 1.
Accordingly, the highest (95.2%) and the lowest (10%) mean disease incidence
was recorded at Jeju and Adama districts, respectively; while the maximum dis-
ease severity (4.67) was observed at Dugda. In general, SLB was prevalent in all
districts assessed with various range of incidence and severity. According to the
farmers, in areas such as Koka, the SLB disease was started to be observed since
2016, which might have been misdiagnosed as purple blotch disease.
3.3. Identification of the Pathogen from Diseased Leaf Samples
Cultural, morphological and pathogenic characteristics of the isolates from symp-
tomatic onion leaf specimen revealed the presence of
S
.
vesicarium
.
Y. Gedefaw et al.
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10.4236/as.2019.108083 1109 Agricultural Sciences
Figure 2. Symptoms of various stages observed during survey: (a) tan spots (lesions); (b)
advanced brown spots; (c) brown lesions advanced to black sporulation; (d) advanced
black sporulation tuning to whitish fruiting structure, mycelia.
Figure 3. Cultural characteristics (a: front and b: back view) of 13-days-old
S
.
vesicarium
on PDA media.
3.4. Cultural and Morphological Characteristics
The in-face colony color was dirty white to light grey (Figure 3(a)). The reverse
colony colors were deep brown, brown and light brown with circular white and
brown alternate band growth pattern (Figure 3(b)). This dirty white and brown
alternate growth and sporulation have found a distinct feature to
S
.
vesicarium
colony growth on PDA media. This result is equivalent to pathogen descriptions
of Hosna
et al
. [25]. The conidia were olive-brown, oval to ovoid, oblong and
ovoid to oblong, are borne on conidiophores that are pale to brown with dark
edges and bands (Figure 4). This is in line with the
S
.
vesicarium
previous de-
scription, Simmon [26]; Basallote-Ureba
et al
. [24] and Woudenberg
et al
.
[15].
3.5. Pathogenecity of Stemphylium vesicarium
Patogenicity test was conducted to confirm whether the pathogen is the primary
cause of the disease observed on onion fields during the survey. Periodical as-
sessment (
i
.
e
.
every week after 1st symptom observation) resulted in small white
tan spots starting from 14 days of post-inoculation (Figure 5). The symptoms
Y. Gedefaw et al.
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10.4236/as.2019.108083 1110 Agricultural Sciences
Figure 4. Conidia (a) and Conidiophores (b) of 13-days-old
S
.
vesicarium
on PDA under
40× compound microscopy.
Figure 5. Symptom expression of
S
.
vesicarium
during pathogenicity test; (a) non-in-
oculated onion (b) inoculated.
have been intensive and extended to all inoculated plants with in a pot and were
as similar to the symptoms observed during the survey. Moreover, successful
re-isolation of the pathogen from artifially inoculated symptomatic leaf tissue af-
firms that the pathogen was pathogenic to onion and that was realy responsible
to massive production loss observed during the survey, which the onion farmers
in the CRV area call it “Ebola of onion”.
4. Conclusion
Based on the literature, this is the first report of the occurrence of stemphylium
leaf blight (
S
.
vesicarium
) on onion in Ethiopia. Complementary work to map its
distribution and intensity in the country, determining other putative hosts and
the best management options will be relevant to manage the disease.
Y. Gedefaw et al.
DOI:
10.4236/as.2019.108083 1111 Agricultural Sciences
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this pa-
per.
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