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Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia



Minyahil Kebede, Girma Adugna and Bekele Hundie
 
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ABSTRACT

Background and Objective: Fusarium Head Blight (FHB) caused by several Fusarium species is a dangerous disease of wheat and small cereals particularly in humid and sub-humid areas throughout the world. A loss due to FHB disease includes both grain yield and quality (that affect human and animal health). This investigation was aimed to identify FHB pathogens that cause blighted spikes in wheat across southwestern Ethiopia. Materials and Methods: A total of 269 single conidial isolates of Fusarium spp. were recovered from 52 FHB samples collected across South Western Ethiopia (SWE). Based on their colony, macroscopic and microscopic features, all the isolates were identified into nine species within the genus Fusarium. Results: Among the nine identified Fusarium species, F. graminearum and F. culmorum were most frequently recovered from blighted wheat spikes in southwestern Ethiopia. All the nine identified Fusarium species were pathogenic to a susceptible Danda’a wheat variety. Based on their AUDPC and spikelet infection severity, F. avenaceum, F. poae, F. lateritium, F. culmorum, F. sambucinum, F. heterosporum and F. graminearum were more aggressive ones that produced higher AUDPC ranging from 546.8-1067.2 and higher spikelet infection severity ranging from 57.8-100%. Conclusion: This study reveals the existence of Fusarium species diversity in Ethiopia that caused FHB on wheat. The pathogenic nature of all identified species indicated that FHB will become a potential disease on wheat in the area.

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  How to cite this article:

Minyahil Kebede, Girma Adugna and Bekele Hundie, 2021. Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia. International Journal of Plant Pathology, 12: 21-31.

DOI: 10.3923/ijpp.2021.21.31

URL: https://scialert.net/abstract/?doi=ijpp.2021.21.31
 

INTRODUCTION

The necrotrophic Fusarium head blight (FHB) of wheat is a major head disease with an overwhelming impact on yield and grain quality mainly during wet seasons that favour FHB disease development and higher mycotoxin accumulation in grains1,2. Generally, up to 19 species in the genus Fusarium were reported in causing FHB disease of wheat3. In addition to wheat, FHB disease infects several crops including barley, oats, rye, corn, canary seed, forage grasses, sugarcane and rice but wheat, barley and maize are the most affected crops4-7.

Kernel infection by FHB pathogens can cause poor seed germination, kernel shrivelling, reduction in the number of kernels per spike, low protein content and low baking quality that contributes to a significant loss both in yield and quality. Besides, the pathogen produces toxic metabolites that have health problems both to humans and animals when consumed8-11.

Globally, due emphasis has been given for FHB because of its impact on grain yield as seedling blight, shrivelled kernels, infertility of spikes2, grain quality such as low protein content, low baking quality12, mycotoxin contaminations in grains and in straws which had health problems when feed by humans and animals8,9.

However, there is a limited research effort done on the FHB disease of wheat in Ethiopia. One of the studies was reported a new novel species F. aethiopicum from 31 Fusarium cf. graminearum isolates originated from the Amhara and Oromia regions of Ethiopia13. This may indicate the existence of species diversity in the country. So far, all the past studies of FHB do not enclose Jimma, Buno-Bedele and West-Wollega zones where wheat is grown as one of the staple food crops. Therefore, this study has aimed to identify, characterize and test the pathogenicity of Fusarium spp. responsible for causing FHB disease of wheat in southwestern Ethiopia.

MATERIALS AND METHODS

Description of study areas: Blighted spikes of wheat were sampled at Dedo, Seka-Chekorsa districts of Jimma zone, Bedele and Gechi districts of the Buno-Bedele zone and Begi district of West-Wollega zone of Oromia region in Table 1.

Sample collection: Four wheat spikes with a typical FHB symptom were sampled per field and placed inside paper bags. The paper bags were labelled with sample code, date of sampling, altitude, latitude, longitude and collectors' names. The samples were placed in the icebox and also ventilated overnight to avoid excess water. Finally, the samples were taken to the Plant Pathology Laboratory of Jimma University College of Agriculture and Veterinary Medicine (JUCAVM) for isolation and identification of the causal agents.

Growth media: Malachite Green Agar (MGA) and Potato Dextrose Agar (PDA) were used to isolating Fusarium species from the samples. Spezieller Nahrstoffarmer Agar (SNA) media with two sterile filter paper pieces had used to enhance the sporulation of isolates. Water agar (3% WA) media had been used for single conidial purification. Besides, PDA and Potato Sucrose Agar (PSA) had used for studying the colony characteristics (such as pigmentation and mycelial growth). All media used in this study had prepared according to 'The Fusarium Laboratory Manual'14. Also, all the media were amended by 250 mg of Chloramphenicol per litre of media to inhibit bacterial contaminants.

Isolation of Fusarium spp.: Eight kernels had separated from each blighted wheat spike sample and surface-sterilized in 4% (v/v) sodium hypochlorite solution for a minute, followed by thrice rinsing in sterilized distilled water. The kernels were well-drained under laminar flow. Then, four kernels had placed on the PDA plate and the other four kernels had placed on the MGA plate.

Table 1: Coordinates, elevations, annual rainfall and mean temperatures of the study area by districts, 2017
Coordinate Temperature (°C)
Zones Districts N E Altitude (m.a.s.l) Rain fall (mm) Minimum Maximum
Jimma Dedoa 07°25' 37°00' 880-2800 1830.36 12.3 25.5
Seka-Chekorssac 07°35' 36°33' 1560-3000 1825.16 10.0 23.0
Buno-Bedele Bedelea 08°27' 36°21' 2012-2162 2051.1 13.0 26.4
Gechic 08°20' 36°40' 1400-2380 1639.0 18.0 25.0
West-Wollega Begib 09°15' 34°45' 1465-2100 1024.4 15.2 27.4
aData obtained from National Meteorology Agency of Ethiopia, Jimma Meteorology Center, 2017, bData obtained from National Meteorology Agency of Ethiopia, Assosa Meteorology Center, 2017, Coordinate and altitude ranges were obtained from the respective district agriculture and natural resource development office, cData obtained from the respective district agriculture and natural resource development office

All plates were labelled, sealed with parafilm and incubated at 25°C. After 4 -5 days of incubation, all Fusarium resembling colonies were cut along with the help of a sterile needle and transferred onto SNA plates. Both sides of the fungal agar block sterile filter paper pieces were placed to enhance conidia formation. The needle used was dipped in ethanol and burned off between each colony transfer. After the colony purification, all the Petri dishes were labelled, sealed with parafilm and incubated at 25°C for 7-17 days until sporulation.

Single conidium isolate development: For single conidial isolation, a small fungal plug was taken from sporulated SNA cultures and transferred to 3% WA and a drop of autoclaved distilled water was added onto the fungal plug and the conidia were dislodged by a sterile glass road. The dislodged conidia were spread over the WA by a sterile glass road spreader and the plates were incubated at 25°C for 24 hrs. Then, hyphal tips derived from a single conidium was cut and transferred to SNA with two sterile filter paper pieces14. The Petri dishes were then labelled, sealed with parafilm and incubated at 25°C for 7-17 days until sporulation. These isolates were used for the examination of microscopic and macroscopic features.

Identification of Fusarium spp.: Isolates of Fusarium recovered from blighted wheat spikes sampled across southwestern Ethiopia was identified into species level based on cultural and morphological characteristics as described by Leslie et al.14 and Refai et al.15.

Pathogenicity test
Experimental design and kernel disinfection: A pathogenicity experiment was conducted from February-June 2018 on Danda'a (a susceptible) bread wheat variety at JUCAVM, Jimma, Ethiopia. RCBD design with three replications had used. Fusarium species were used as test treatments, while sterile distilled water was used as a control. The experimental units were plastic pots (having a size of 15×11×15 cm), which had filled with an autoclaved potting mix (1:3:1 v/v sand/peat/compost). Before sowing, the wheat kernels had washed under running tap water for 5 min. Then, disinfected in 75% ethanol for 30 seconds and 0.5% NaOCl (sodium hypochlorite) solution for a minute. Finally, the kernels were rinsed twice in sterile distilled water and allowed to dry under laminar flow16. The four well-dried kernels had seeded at a depth of 2 cm in each pot. Each pot was fertilized with 5 g urea before emergence, 5 g NSP at tillering and 5 g urea at booting and also watered twice daily.

Preparation of inocula: The nine identified Fusarium spp. were recovered on SNA with sterile filter paper and incubated for 7-17 days at 25°C until sporulation. Then, 10 mL of sterilized distilled water was poured onto each sporulated plate and the conidia were dislodged by using a sterile glass road cell spreader. The suspension was filtered through two layers of sterilized cheesecloth16 and the final concentration was adjusted to 5×105 conidia mL–1 with the help of a hemocytometer. From the adjusted inoculum, 200 μL of each Fusarium species was kept in a 5 mL Falcon tube at 4°C pending inoculation17,18.

Inoculation: A single centrally positioned floret of two spikes per pot was injected19 at Zadok’s growth stage 65 by the already prepared 10 μL inoculum of each Fusarium species. Control (check) spikes were inoculated in the same way by 10 μL of sterile distilled water. Simultaneously, the spikes were tagged and covered with polythene bags for 48 hrs to maintain high humidity that can facilitate infection process21-23.

Collected data
Fusarium morphology data: Primary and secondary morphology data were collected for identification of Fusarium isolates into species level according to the description of Fusarium species described by Leslie et al.14, He et al.20 and Refai et al.15.

Primary characters such as:

Macroconidia characteristics like phialides, shape, size, number of septa, the shape of the apical and basal cells were noted
Microconidia characteristics including presence or absence of microconidia, if present their shape, size and how they are formed (phialides) were noted
Chlamydospores presence or absence, if present their form (chain or single)

Secondary characters:

Colony morphology features include colour on PDA, pigmentation and hyphal colony growth on PDA and PSA

Pathogenicity test data: Blighted spikelets per spike due to the infection of inoculated Fusarium spp. was carefully inspected every week. The spikelet bleaching severity caused by each Fusarium spp. was recorded as a percentage of blighted spikelets over the total number of spikelets per spike24 at 7, 14, 21 and 28 days after inoculation17,20,25. Finally, each inoculated spike was separately taken to the laboratory and re-isolation was performed to confirm the identity of the test pathogen.

Data analysis: From the pathogenicity test experiment, the Area Under Disease Progress Curve (AUDPC) for the nine Fusarium spp. was determined as described by Madden et al.26:

Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia

Where:

AUDPC = Area under disease progress curve
n = Total number of observation days at the ith observation
yi = Spikelet bleaching severity at the ith observation
t = Time at the ith observation

Analysis of variance for spikelet bleaching severity and AUDPC data was performed using the general linear model procedure of SAS version 9.3 statistical software27. The means were separated by the LSD test at a probability level of 0.05. The spikelet infection rates of each inoculated species were determined by Minitab 17 software. The RCBD model used for analyzing AUDPC and spikelet bleaching severity is described as follows:

Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia

Where:
Yij = Response (AUDPC or spikelet bleaching severity) for treatment i observed in block j
μ = Overall mean
α = Effect of the ith treatment
β = Effect of the jth block
εij = Error term for the ith treatment in the jth block

Finally, the aggressiveness of Fusarium spp. used in pathogenicity test on Danda’a wheat variety was determined from spikelet infection severity and AUDPC28,29.

RESULTS AND DISCUSSION

Fusarium spp. associated with blighted wheat spikes: A total of 269 single conidial purified Fusarium isolates had recovered from blighted wheat spikes collected during the 2017 main cropping season in Jimma, Buno-Bedele and West-Wollega zones of Oromia, Southwestern Ethiopia. Based on their cultural and microscopic characteristics as described by Leslie et al.14 and Refai et al.15, all the identified isolates were grouped into nine Fusarium species (Fig. 1-9a-c) with varied isolation frequency across the study area in Table 2. The variation may be due to factors such as field location, climatic conditions, soil management, crop rotation and cultivation methods30.

Based on this provisional identification, F. culmorum (Fig. 2a-c) and F. ussurianum (Fig. 5a-c) were isolated from blighted wheat spikes which were not reported by the previous study conducted in Ethiopia, though this needs further confirmation. On the other hand, F. graminearum, F. avenaceum, F. poae, F. semitectum, F. sambucinum, F. heterosporum and F. lateritium had recovered from stored wheat grains and blighted wheat spikes sampled from Arsi, Bale, Gojam, Gonder, Shoa and Wollo areas.

Among the nine species, F. graminearum and F. culmorum were the two most frequently isolated species comprised of 29.0 and 26.4% of the total number of Fusarium isolates, respectively. Whereas, F. avenaceum, F. poae, F. ussurianum, F. semitectum, F. sambucinum and F. lateritium had made up of 10.4, 7.4, 6.7, 6.3, 6.0 and 6.0%, respectively. On the other hand, the least isolated species was F. heterosporum which had only 1.9% of the total isolates (Table 2).

Table 2: Isolation frequency (%) of identified Fusarium spp. from wheat blighted heads in SWE, 2017 main cropping season
Fusarium species
N
PDA
N
MGA
TN
TIF
F. graminearum Schwabe (Fig. 1a-c)
46
28.6
32
29.6
78
29.0
F. culmorum (W.G. Smith) Saccardo (Fig. 2a-c)
32
19.9
39
36.1
71
26.4
F. avenaceum (Fries) Saccardo (Fig. 3a-c)
21
13.0
7
6.5
28
10.4
F. poae (Peck) Wollenweber (Fig. 4a-c)
12
7.5
8
7.4
20
7.4
F. ussurianum T. Aoki, Gagkaeva, Yli-Mattila, Kistler and O'Donnell (Fig. 5a-c)
12
7.5
6
5.6
18
6.7
F. semitectum Berkeley and Ravenel (Fig. 6a-c)
12
7.5
5
4.6
17
6.3
F. sambucinum Fückel sensus tricto (Fig. 7a-c)
10
6.2
6
5.6
16
6.0
F. lateritium Nees (Fig. 8a-c)
13
8.1
3
2.8
16
6.0
F. heterosporum Nees ex Fries (Fig. 9a-c)
3
1.9
2
1.9
5
1.9
Total
161
108
269
N: Number of isolates, PDA: % of isolates on potato dextrose agar, MGA: % of isolates on Malachite-Green Agar; TN: Total number frequency (%), TIF: Total isolation frequency (%)


Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 1(a-c):
(a) F. graminearum colony on PDA, (b) Conidiophore of F. graminearum and (c) Conidia of F. graminearum


Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 2(a-c):
(a) F. culmorum colony on PDA, (b) Conidiophore of F. culmorum and (c) Conidia of F. culmorum


Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 3(a-c):
(a) F. avenaceum colony on PDA, (b) Conidiophore of F. avenaceum and (c) Conidia of F. avenaceum

These revealed that F. graminearum and F. culmorum were the two most predominately isolated species followed by F. avenaceum from blighted wheat spikes in southwestern Ethiopia. Previously in Ethiopia, F. graminearum and F. avenaceum were reported among the predominant species isolated from stored wheat grains and blighted wheat spikes sampled from Arsi, Bale, Gojam, Gonder, Shoa and Wollo areas. Further, in neighbouring country Kenya, these two species (F. graminearum and F. avenaceum) were predominately isolated from wheat spikes in Narok County and kernels in Nakuru County31.

Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 4(a-c):
(a) F. lateritium colony on PSA, (b) Conidiophore of F. lateritium and (c) Conidia of F. lateritium


Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 5(a-c):
(a) F. poae colony on PDA, (b) Conidiophore of F. poae and (c) Conidia of F. poae


Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 6(a-c):
(a) F. semitectum colony on PDA, (b) Conidiophore of F. semitectum and (c) Conidia of F. semitectum

Distribution of Fusarium spp. in southwestern Ethiopia: F. graminearum, F. culmorum, F. lateritium, F. avenaceum, F. poae and F. heterosporum were isolated from samples collected from the five assessed districts in southwestern Ethiopia in Table 3. However, F. sambucinum, F. ussurianum and F. semitectum were isolated from four assessed districts (Table 3).

The most dominant F. graminearum was mainly isolated from samples of the Buno-Bedele zone (44.9%) and West-Wollega zone (34.6%). In particular, Begi, Bedele and Gechi districts were attributed 24.4, 23.1 and 21.8% of F. graminearum isolation, respectively (Table 3).

Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 7(a-c):
(a) F. ussurianum colony on PSA, (b) Conidiophore of F. ussurianum, (c) Conidia of F. ussurianum


Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 8(a-c):
(a) F. sambucinum colony on PDA, (b) Conidiophore of F. sambucinum, (c) Conidia of F. sambucinum


Image for - Identification of Fusarium Species Responsible to Cause Wheat Head Blight in Southwestern Ethiopia
Fig. 9(a-c):
(a) F. heterosporum colony on PSA, (b) Conidiophore of F. heterosporum, (c) Conidia of F. heterosporum

Whereas, the second predominant F. culmorum was frequently isolated from samples of the Buno-Bedele zone (59.2%) and Jimma zone (25.4%). It was mainly recovered from samples of Gechi district (39.4%), Bedele district (19.7%) and Seka-Chekorsa (19.7%) (Table 3). The third predominant F. avenaceum was mainly isolated from samples of Jimma zone (53.6%) particularly in Seka-Chekorsa that attributed 38.5% isolation frequency (Table 3).

The occurrence and distribution of Fusarium species can vary with the changing climate, crop rotation, cultivar resistance and interactions among different species30,32.

Table 3: Distribution (%) of Fusarium spp. by zones and districts in southwestern, 2017
Distribution by zones Distribution by districts
Fusarium spp.
N
Jimma
Buno-Bedele
West-Wollega
Dedo
Seka-Chekorsa
Bedele
Gechi
Begi
F. graminearum
78
16 (20.5)
35 (44.9)
27 (34.6)
8 (10.3)
8 (10.3)
18 (23.1)
17 (21.8)
19 (24.4)
F. culmorum
71
18 (25.4)
42 (59.2)
11 (15.5)
4 (5.6)
14 (19.7)
14 (19.7)
28 (39.4)
8 (11.3)
F. lateritium
16
6 (37.5)
6 (37.5)
4 (25.0)
1 (6.3)
5 (31.3)
3 (18.8)
3 (18.8)
3 (18.8)
F. avenaceum
28
15 (53.6)
7 (25.0)
6 (21.4)
5 (19.2)
10 (38.5)
2 (7.7)
5 (19.2)
4 (15.4)
F. poae
20
5 (25.0)
6 (30.0)
9(45.0)
3 (15.0)
2 (10.0)
3 (15.00)
3 (15.0)
5 (25.0)
F. sambucinum
16
4 (25.0)
8 (50.0)
4 (25.0)
4 (25.0)
-
3 (18.8)
5 (31.3)
1 (6.3)
F. ussurianum
18
9 (50.0)
9 (50.0)
-
4 (22.2)
5 (27.8)
6 (33.3)
3 (16.7)
-
F. semitectum
17
9 (52.9)
5 (29.4)
3 (17.7)
4 (23.5)
5 (29.4)
-
5 (29.4)
2 (11.8)
F. heterosporum
5
2 (40.0)
2 (40.0)
1 (20.0)-
1 (20.0)
1 (20.0)
1 (20.0)
1 (20.0)
1 (20.0)
Values in parenthesis are percent frequency; : Shows the species does not recover from the samples


Table 4: Blighted spikelet severity and AUDPC of Fusarium spp. under lath-house, 2018
Spikelet infection severity
Fusarium spp. 7 DAI
14 DAI
21 DAI
28 DAI
AUDPC
r
R2 (%)
F. avenaceum 2.6cd
30.5ab
70.7a
100.0a
1067.2a
0.51**
64.62
F. poae 9.6a
35.9a
74.4a
74.5ab
1066.3a
0.52**
85.58
F. sambucinum 6.1abc
16.3abcd
52.3abc
83.1a
792.4ab
0.11
4.5
F. lateritium 5.5bc
21.9abc
54.9ab
85.6a
856.2ab
0.43**
70.45
F. culmorum 6.0abc
20.3abcd
46.7bc
88.9a
801.3ab
0.52*
44.51
F. heterosporum 6.4ab
22.9abc
40.9bc
57.8ab
670.9b
0.26*
45.29
F. graminearum 4.9bc
13.2bcd
29.1cd
66.8ab
546.8b
0.21**
43.19
F. ussurianum 0.0d
3.0cd
7.1de
29.8cd
175.2c
0.42**
60.36
F. semitectum 0.0d
0.0d
0.0e
33.2bc
116.2c
0.12
5.58
Sterilized distilled water 0.00d
0.0d
0.0e
0.0c
0.0c
-
-
LSD 3.8
20.4
23.7
45.8
358.7
Mean values in a column with different letters are significant at p<0.05, AUDPC: Area under disease progress curve, DAI: Days after inoculation, LSD: Least significant difference, r: Rate of spikelet bleaching

For instance, in some parts of Europe, the predominant species were varied among F. graminearum, F. poae, F. avenaceum and F. culmorum32, however, F. graminearum was also reported in displacing the F. culmorum33. Moreover, a four-year study in Belgium revealed that the most frequent causal agent of FHB in wheat was F. graminearum mainly in areas where corn was cultivated and F. culmorum, mainly in areas where small grains were grown34. This revealed the effect of cultural practices on Fusarium species abundance.

Pathogenicity test: The pathogenicity of all Fusarium spp. identified in this study was assessed using point (single spikelet) injection method18. The results indicated that all the tested Fusarium spp. caused FHB symptoms on spikes of Danda’a variety. However, no FHB symptoms were observed on spikes inoculated with sterile distilled water (control). Re-isolation from the kernels of inoculated spikes agrees with descriptions of the inoculated species, which confirms their pathogenicity under Lath-house conditions.

Fusarium spp. had shown significantly varied spikelet bleaching severity and AUDPC on Danda'a wheat variety in Table 4. F. avenaceum was the most aggressive species that caused the highest spikelet bleaching severity of 100% at 28 Days After Inoculation (DAI) and AUDPC of 1067.2 on Danda'a variety (Table 4). Statistically comparable spikelet bleaching severities had produced by F. culmorum, F. graminearum, F. lateritium, F. sambucinum, F. poae and F. heterosporous. Likewise, F. poae, F. sambucinum, F. lateritium and F. culmorum were generated statistically similar AUDPC as compared to that of F. avenaceum. However, F. ussurianum and F. semitectum had produced the lower AUDPC of 175.2 and 116.2, respectively (Table 4).

All nine Fusarium species had shown the different rates of FHB disease development on Danda'a wheat variety (Table 4). Seven of the tested species had caused FHB symptoms at 7 DAI, while the others at 14 and 28 DAI (Table 4). This finding almost agrees with the comparative aggressiveness study conducted in Canada that reported F. graminearum, F. avenaceum, F. culmorum and F. poae had produced visible spikelet bleaching at 21 and 28 DAI on wheat spikes35. On the other hand, delayed symptom development was observed by F. ussurianum and F. semitectum after seven and 21 DAI (Table 4).

Based on spikelet bleaching severity and AUDPC results, F. avenaceum, F. poae, F. sambucinum, F. lateritium, F. culmorum, F. heterosporum and F. graminearum were more aggressive on Danda'a wheat variety. These seven species had caused spikelet bleaching severity and AUDPC beyond or equal to 57.8 and 546.8%, respectively (Table 4). Whereas, F. semitectum and F. ussurianum were showed less aggressiveness on Danda'a variety with spikelet bleaching severity of 33.19 and 29.78% and AUDPC of 116.2 and 175.2, respectively (Table 4). These findings concurred with the aggressiveness study that reported F. graminearum and F. culmorum as an aggressive species causing more than 35% of spikelet bleaching severity of wheat in Canada35.

In addition to causing blighted wheat spikes, F. culmorum, F. graminearum and F. avenaceum had responsible for crown rot of bread wheat and durum wheat in Turkey36 and root rot of corn, soybean and wheat in Nebraska37. Likewise, F. culmorum had been reported in causing higher seedling blight, while F. graminearum had responsible for causing severe crown rot of wheat38,39.

CONCLUSION

A total of 269 single conidial purified isolates had recovered from blighted wheat spikes sampled across Jimma, Buno-Bedele and West-Welega zones of Oromia, southwestern Ethiopia. Based on their cultural and microscopical characteristics, all isolates had classified into nine Fusarium species. Among the nine species, F. graminearum and F. culmorum were the most predominant ones, followed by F. avenaceum in southwestern Ethiopia. Besides, all the nine species had pathogenic and F. avenaceum, F. poae, F. sambucinum, F. lateritium, F. culmorum, F. heterosporum and F. graminearum were shown more aggressiveness on Danda'a wheat variety.

SIGNIFICANCE STATEMENT

This study discovered nine pathogenic Fusarium species responsible for the FHB of wheat in southwestern Ethiopia. This study noticed two Fusarium species namely F. culmorum and F. ussurianum that were not reported in Ethiopia. Besides, this investigation identified F. graminearum and F. culmorum as the most frequent and the more aggressive species that caused FHB on wheat in the study area. Therefore, this study will help the researchers to uncover why these species are dominant in the area and also help researchers to devise intervention strategies.

ACKNOWLEDGMENT

The authors would like to thank the Ethiopian Institute of Agricultural Research and Assosa Agricultural Research Center for their financial supports. We also extend a sincere thanks to Jimma University College of Agriculture and Veterinary Medicine (JUCAVM) Department of Horticulture and Plant Science for allowing us to use their plant pathology laboratory and Lath-house facilities for the successful execution of this work. Also, our gratitude goes to Kulumsa Agricultural Research Center for the provision of the susceptible test crop, Danda'a wheat variety, for the pathogenicity test.

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