The field survey was conducted during the 2019 cropping season. The survey 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.

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

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.

^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.

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] .

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 confirm colonization by S. vesicarium. After 4 days of incubation, conidial and mycelial 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 filtered 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 greenhouse. 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.

During the survey, the overall look of onion fields affected by the disease is depicted 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, reduced bulb size (Figure 1(b)) and associated yield loss was observed whenever matured onion fields were encountered during the survey. This was further confirmed from the communication made with producers during the assessment. Due to this massive appearance of the disease symptoms and maximum production 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. Overall, the symptoms observed during the survey are similar with symptoms description of SLB by Basallote-Ureba et al. [24] .

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 disease 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.

Cultural, morphological and pathogenic characteristics of the isolates from symptomatic onion leaf specimen revealed the presence of S. vesicarium.

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 description, Simmon [26] ; Basallote-Ureba et al. [24] and Woudenberg et al. [15] .

Patogenicity test was conducted to confirm whether the pathogen is the primary cause of the disease observed on onion fields during the survey. Periodical assessment (i.e. every week after 1^st symptom observation) resulted in small white tan spots starting from 14 days of post-inoculation (Figure 5). The symptoms

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 affirms 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”.