Evaluation of Fusarium Head Blight in Wheat Associated With Agronomic Practices in Southwest and Central Ethiopia
Abstract
Fusarium head blight (FHB) is caused primarily by Fusarium graminearum (Gibberella zeae L.) and is a major problem to wheat production in Ethiopia. It directly affects the yield of wheat and indirectly contaminates products due to mycotoxins. A field survey was conducted in Central and Southwest Ethiopia to assess the intensity of FHB of wheat and its association with agronomic practices during the 2019/2020 cropping season. A total of 144 fields in 12 districts were surveyed and analysed using GENMOD technique in SAS. Logistic regression was used to test the association of FHB with agronomic factors. The result showed that FHB was prevalent in all surveyed fields and widely distributed with 100% incidence in some fields. FHB epidemic was favoured in areas with humid weather, and most notably includes Tello, Deddo, Mencho, She-Bench and Adiyo districts in Southwest Ethiopia, but was suppressed in Endegagn, Soddo and Wolisso districts of Central Ethiopia. These results confirm that Southwest Ethiopia was severely affected by FHB than Central Ethiopia. High FHB incidence (≥75%) and severity index (≥55%) were associated with potato, teff and maize as preceding crops; less frequent ploughing; late planting time (September and beyond it); and Kakaba’a’, Kingbird and Mekuye as recently sown wheat varieties. Low FHB intensity had high probability of association with planting in July, peas and beans as preceding crops and Triticale, Hidase and Shorima as a recently sown wheat varieties. The study suggests that the use of peas and beans as a preceding crop, frequent ploughing, use of less infected wheat varieties and planting in July could be used in designing integrated disease management options to reduce FHB epidemic in wheat.
1. Introduction
Wheat (Triticum spp.) is the most important staple food crop in the world. Due to urbanization and industrialization, there is an increasing demand in several countries. Wheat is a major source of starch and energy, and it also provides substantial amounts of a number of components that are essential or beneficial for health, which includes proteins, vitamins (B vitamins), dietary fibre and phytochemicals [1].
Global wheat production reached 771 million tonnes in 2021, indicating a growth record of over 31% since 2000 [2]. In Ethiopia, the total wheat cultivated area was 2,259,772.87 ha for the year 2020/2021 in both seasons, which comprised of private peasant holdings and large-scale farms. The estimated wheat production was 6,323,784.45 tonnes with a national average yield of about 3.05 t/ha [3]. The obtained yield of 3.05 t/ha is lower than the global wheat yield average of 3.5 t/ha. These differences could be partly explained by differences in crop management and agroecology [4]. Ethiopia is widely regarded as the centre of genetic diversity in durum wheat [5]. Both durum (Triticum turgidum L. var durum) and bread wheat (Triticum aestivum L.) are mainly cultivated in Ethiopia, while other wheat species are produced to a lesser extent. Wheat production in Ethiopia is affected by biotic and abiotic factors. Various pathogens which include fungi, bacteria and viruses infect wheat with share of an average global losses of 21.5% yield losses of wheat ranging from 10.1 up to 28.1% [6]. Among these, a wide range of biotic stresses, such as many wheat diseases (rusts, septoria, fusarium etc.), play a considerable role in limiting production beside poor agronomic practices [7–9]. Abiotic factors include soil acidity, decrease in soil fertility, extreme moisture, heat stress, production systems focusing on mono-cropping and climate change [7].
Fusarium head blight (FHB) is a disease caused by the fungus Fusarium graminearum (Gibberella zeae) and is rated as one of the most devastating diseases affecting wheat and barley [9]. It is also referred to as Fusarium ear blight, scab or head fusariosis [10] and described as a disease of small-grain cereals [11]. The extent of damage due to FHB disease is variable in the world due to the existence of different environmental and agroecological conditions. As it was mentioned by McMullen et al. [12], the production of wheat and barley was declined due to FHB in United States from1992 to 2000. The epidemics of FHB caused in 1982 in United States which makes in a 4% reduction of total wheat production equivalent to 2.72 million metric tonnes [12, 13]. The presence of FHB in two-thirds of provinces in China was reported affecting more than 7 million hectares of wheat-growing areas with yield reduction of more than 1 million tonnes [14]. It was stated that FHB results in about 10%–70% yield loss during epidemic years [14]. Different FHB epidemics were also reported from Argentinian [15], Canada [16] and Japan [17] in different years.
Twenty-five years after the report of the occurrence of FHB by Bekele and Karr [18] at varying incidence and severity rates on various experimentation, research and farmers sites, FHB disease of wheat was reported with an incidence of 10% to 47% at farmer’s fields during 2014 main cropping season in Ari district of South Omo Zone, Southern Nation, Nationalities and Peoples Regional State (SNNPRS), Ethiopia [19].
FHB epidemics were increasing highly and frequently in the past few years worldwide and particularly Ethiopia indicated from the occurrence of epidemics during the 2022 main cropping season [20]. Surveys on FHB (scab) have been made in some wheat-growing areas, and the disease was found to cause up to 90% head blight in some years with extended rainy seasons in the country [21]. Compared to its importance, adequate attention was not given to the study of FHB disease of wheat in relation especially to its occurrence, distribution and significant yield reduction in Ethiopia [22, 23]. This was discussed by Mengesha et al. [24], from the serious FHB epidemic as an outbreak occurred in southern Ethiopia during the 2017 and 2018 cropping seasons. This indicated the need for research concerning direct and indirect effects of FHB such as the contamination of infected crops by mycotoxins.
Wheat is highly susceptible to FHB infection when the crop is at the flowering to soft dough stages [25]. Infected crop debris serves as the primary source of the initial inoculum of FHB. Its intensity is influenced by weather factors, inoculum density, host range and farmer management practices [26, 27]. Weather factors such as high temperatures (25–30°C), heavy dew (>90%) and frequent precipitation for 48–72 h during pre- and postanthesis periods augment the intensity of FHB [12]. Temperature fluctuations within the range of 10–30°C in the presence of moisture is a suitable requirement for the immense infection of the pathogen [28, 29].
The initial symptoms of FHB occur immediately after flowering. Fusarium pathogens proliferate and spread rapidly intracellularly, followed by the development of FHB symptoms, including necrosis. Diseased spikelets exhibit premature bleaching as the pathogen grows and spreads throughout the head. Infected spikelets first appear water-soaked, lose their chlorophyll and become straw-coloured. When warm, humid weather conditions prevail, pinkish red mycelia and conidia develop abundantly in the infected spikelets. The infection spreads further to adjacent spikelets with ultimate shrivelled and discoloured or through the entire head. Infected kernels become shrivelled and discoloured with a white, pink or light brown scaly appearance [26, 28–30].
In Ethiopia, the yield loss due to FHB was explained based on the response of wheat cultivars across locations which was indicated by the relation between FHB severity and yield loss which occurred in each location [31]. In other study on the response of wheat genotypes, the highest yield loss (58.20%) was reported on commonly and widely grown but also susceptible Ogolcho wheat variety in the area. These conditions showed that the disease continued as threat to wheat crop production in the country [32].
Despite its potential to cause significant yield losses in wheat, limited works have been undertaken on the distribution and associated biophysical factors affecting development of wheat FHB [22, 23, 33, 34]. A detailed understanding of the present status of FHB in wheat and the factors associated with disease development is essential to develop relevant recommendations. This study was conducted to assess (1) the incidence and severity of wheat FHB in Southwest and Central Ethiopia and (2) to determine the association between FHB disease intensity and agronomic practices.
2. Materials and Methods
2.1. Description of the Study Area
Wheat (T. aestivum L.) fields were assessed during the 2019/2020 cropping season in wheat-producing areas in Central and Southwest Ethiopia. The survey covered districts selected from zones in Oromia and SNNPRS of the country exhibiting variable agroclimatic conditions (Figure 1). They study area is located at 6°15′55.05″ N and 9°47.927″ N latitude and 35°44′15.70″ E and 38°38′55.97″ E longitude, with altitudes ranging from 1862 to 2618 m above sea level (m.a.s.l.).
Meteorology data were obtained from Jimma Meteorological Station. The mean annual rainfall in the surveyed areas ranged from 103.22 mm in Gurage zone to 239.03 mm in Jimma zone, whereas the temperature varied from 16.8°C in Jimma in January to 24.5°C in Bench-Maji zones in October (Figures 2 and 3). The relative humidity ranged from 33.9% in Southwest Shoa in February to 90.3% in Buno Bedelle zone in August during assessment year (Figure 4).
2.2. Sampling Method
The fields assessed were chosen randomly using purposive sampling. Wheat fields in the distance range of 5–8 km were considered. After the random choice of wheat fields in each peasant association (PA), sample and data were taken by walking diagonally in the field and considering three of 1 m × 1 m quadrants. Three subplots from each field were combined to obtain a single field representation. The total number of wheat heads was counted in each quadrant, and subsequent FHB-symptomatic plants with varying degrees of disease on each spike were scored and averaged. Spikes of symptomatic wheat plants were then detached and placed in a paper bag with the required specific information. The samples were stored in a laboratory refrigerator at 4°C until statistical analysis.
2.3. Disease Assessment
During the FHB assessment, major wheat-producing 12 districts were selected from six zones based on the production area coverage and yield potential. Thus, district selection was carried out through discussions with district agriculture office experts and development agents. In each District, three PAs and four wheat fields per PAs were considered to determine the distributions and disease intensity of FHB. In the assessment area, wheat and triticale fields were sampled in the 2019/2020 cropping season, comprising different wheat agroecologies. Wheat fields were chosen randomly in each PA; households were interviewed to obtain data on agronomic practices. Interviews captured information on biophysical data, such as cropping pattern, frequency of ploughing, method and time of sowing, previous crops, frequency and method of weeding, fertilizer application and recently sown varieties.
2.4. Data Collection
FHB disease incidence and severity data were collected visually from the beginning of anthesis (ZGS 58-83) through early dough development [35]. Disease quantification was performed by estimating disease incidence as the percentage of infected spikes from the total heads [36]. Field severity was determined by multiplying the number of symptomatic heads by individual scores on the modified Horsfall–Barrett’s scale. Field severity was then categorized as field severity (the average score of all assessed wheat spikes per field) and infected head severity (the average score of only infected wheat spikes per field) [37]. Biophysical data were analysed using logistic regression analysis in SAS version 9.3 to determine the association between biophysical characteristics, FHB incidence and the severity index of wheat. Survey data weres arranged as random factors for a three-stage nested design analysis for disease severity and disease incidence using proc GENMOD SAS 9.3 version [38].
2.5. Data Analysis
The data from the field assessment were summarized using descriptive statistics in SPSS version 20 to explain the distribution and relative importance of FHB in wheat. The GENMOD in SAS 9.3 statistical software (SAS, 2010) was used to analyse the incidence and severity of FHB. The overall means of disease incidence and severity were computed, and comparisons were made among districts using χ2 Duncan’s multiple range test of SAS 9.3 statistical software [38]. The disease incidence and severity were classified as described by Chemeda and Yuen [39]. Thus, <55% and >55% were chosen for disease severity, and <75% and >75% were considered for disease incidence, yielding a binary dependent variable.
Contingency table of disease intensity with independent variables were constructed to represent the bivariate distribution of fields [39]. The association of agronomic characteristics with the response variables of FHB disease in wheat was analysed using logistic regression.
Disease severity was measured as the percentage of infected spikelet(s) within the spike using a 0–9 scale [37, 40], where 1 = no symptoms, 2 = <5%, 3 = 5%–15%, 4 = 16%–25%, 5 = 25%–44%, 6 = 46%–65%, 7 = 66%–85%, 8 = 86%–95% and 9 = 96%–100%.
3. Results
3.1. General Characteristics of the Wheat Fields
The surveyed wheat fields across the districts had an altitude ranging from 1862 (Mencho) to 2618 (Endegagn) m.a.s.l., with most of the surveyed fields (75.7%) located at an altitude of >2000 m.a.s.l., of which 64% (92) of the fields were at 2000–2500 m.a.s.l. Farmers practiced monocropping, shifting cultivation, intercropping and crop rotation in wheat production systems, which are summarized as 89% (128) of solely cropped wheat fields and 11% (16) intercropped fields. About 56% (80) of the wheat fields were rotated with other crops. Crops rotated with wheat in the surveyed fields included teff (Eragrostis tef [Zucc.] Trotter), maize, peas, beans, potatoes and others (cabbage, onion, garlic and enset seedlings (Ensete ventricosum [Welw.] Cheesman). The survey found that 10.42% and 23.2% of fields were continuously planted with wheat and shifting cultivation, respectively.
The sources of seed are diverse which includes their own savings, exchanges with farmers, private seed enterprises, government or nongovernment organizations (NGOs) and farmer unions. The majority of the farmers 39.6% obtained seeds from government organizations/NGOs, while others 29.86% acquired it through exchanges with farmers. Only few farmers 8.33% depend on own saved seeds. Planting began in late June and continued until early September. The majority of farmers (33.33%) started sowing in July with the minority (11%) in June.
The cropping patterns comprised of row-planting and broadcasting at 72% and 28%, respectively. Weeds are an important problem throughout the growing stage; hence, most farmers frequently employ various weeding methods. Farmers weeded three, four and more than four times per growing season represented 7.64%, 46.54% and 45.83%, respectively. A proportion of 20.83% of the respondents practice manual weeding, while 39.85% used herbicides only, and 39.85% used both manual weeding and herbicides (Table 1).
| Variable | Variable class | Assessed fields | Disease incidence (%) | Severity index (%) | ||
|---|---|---|---|---|---|---|
| <75% | ≥75% | <55% | ≥55% | |||
| Districts | Deddo | 12 | 0 | 12 | 2 | 10 |
| Mencho | 12 | 0 | 12 | 3 | 9 | |
| Gechi | 12 | 8 | 4 | 10 | 2 | |
| Bedelle | 12 | 3 | 9 | 7 | 5 | |
| Wolisso | 12 | 12 | 0 | 12 | 0 | |
| Kersa Malema | 12 | 3 | 9 | 6 | 6 | |
| Soddo | 12 | 5 | 7 | 8 | 4 | |
| Endegagn | 12 | 12 | 0 | 11 | 1 | |
| Adiyo | 12 | 0 | 12 | 2 | 10 | |
| Tello | 12 | 0 | 12 | 0 | 12 | |
| She-Bench | 12 | 1 | 11 | 2 | 10 | |
| Goldiya | 12 | 0 | 12 | 0 | 12 | |
| Altitude | ≤2000 | 35 | 5 | 30 | 11 | 24 |
| 2000–2500 | 92 | 28 | 64 | 40 | 52 | |
| >2500 | 17 | 12 | 5 | 12 | 5 | |
| Recycling of seed | Yes | 68 | 31 | 37 | 39 | 29 |
| No | 72 | 11 | 61 | 21 | 51 | |
| Yes, but not after FHB information | 4 | 3 | 1 | 3 | 1 | |
| Production system | Monocropping | 15 | 11 | 4 | 11 | 4 |
| Shifting cultivation | 33 | 8 | 25 | 14 | 19 | |
| Intercropping | 16 | 4 | 12 | 5 | 11 | |
| Crop rotation | 80 | 22 | 58 | 33 | 47 | |
| Seed source | Private seed enterprises | 10 | 6 | 4 | 6 | 4 |
| Farmer cooperatives/unions | 22 | 11 | 11 | 13 | 9 | |
| Individual farmers | 43 | 15 | 28 | 21 | 22 | |
| Own seeds | 12 | 1 | 11 | 3 | 9 | |
| Governments/NGOs | 57 | 12 | 45 | 20 | 37 | |
| Time of sowing | June 19 (earlier) | 16 | 6 | 10 | 10 | 6 |
| July 19 (appropriate) | 48 | 24 | 24 | 27 | 21 | |
| August 19 (late) | 35 | 12 | 23 | 18 | 17 | |
| September 19 (late) | 32 | 0 | 32 | 3 | 29 | |
| Not known | 13 | 3 | 10 | 4 | 9 | |
| Method of sowing | Broadcasting | 40 | 7 | 33 | 13 | 27 |
| Row seeding | 104 | 38 | 66 | 50 | 54 | |
| Crop rotation | Yes, I use | 113 | 33 | 80 | 50 | 63 |
| No, I do not use | 31 | 13 | 18 | 13 | 18 | |
| Previous crops | Teff | 15 | 6 | 9 | 10 | 5 |
| Maize | 42 | 4 | 38 | 9 | 33 | |
| Potato | 6 | 0 | 6 | 0 | 6 | |
| Beans | 11 | 5 | 6 | 6 | 5 | |
| Peas | 27 | 15 | 12 | 18 | 9 | |
| Others | 43 | 15 | 28 | 20 | 23 | |
| Method of weeding | Hand weeding only | 30 | 11 | 19 | 14 | 16 |
| Herbicide application only | 57 | 12 | 45 | 22 | 35 | |
| Hand weeding and herbicide | 57 | 22 | 35 | 27 | 30 | |
| Frequency of weeding | Thrice | 11 | 5 | 6 | 3 | 8 |
| Four times | 67 | 14 | 53 | 24 | 43 | |
| More than four times | 66 | 26 | 40 | 36 | 30 | |
| Frequency of ploughing | Twice | 2 | 0 | 2 | 1 | 1 |
| Thrice | 18 | 2 | 16 | 3 | 15 | |
| Four times | 44 | 12 | 32 | 16 | 28 | |
| Five times | 44 | 16 | 28 | 22 | 22 | |
| More than five times | 36 | 15 | 21 | 21 | 15 | |
| Fertilizer | Yes, I use | 128 | 45 | 83 | 62 | 66 |
| No, I do not use | 16 | 0 | 16 | 1 | 15 | |
| Pesticides | Fungicides | 38 | 9 | 29 | 14 | 24 |
| Insecticide | 1 | 1 | 0 | 1 | 0 | |
| Seed treatment chemicals | 6 | 3 | 3 | 4 | 2 | |
| No chemicals | 99 | 32 | 67 | 44 | 55 | |
| Recent varieties sown | Danda’a’ | 30 | 9 | 21 | 15 | 15 |
| Ogolcho | 8 | 5 | 3 | 6 | 2 | |
| Hidase | 35 | 10 | 25 | 14 | 21 | |
| Mekuye | 11 | 5 | 6 | 5 | 6 | |
| Kingbird | 5 | 0 | 5 | 1 | 4 | |
| Digelu | 10 | 4 | 6 | 5 | 5 | |
| Shorima | 14 | 3 | 11 | 4 | 10 | |
| Kakaba | 8 | 2 | 6 | 5 | 3 | |
| Triticale | 4 | 4 | 0 | 4 | 0 | |
| Simba | 7 | 0 | 7 | 0 | 7 | |
| Local variety | 12 | 3 | 9 | 4 | 8 | |
Many wheat growers in the surveyed area used teff, maize, potatoes, beans, peas and others as previous crops. Five wheat field tillage practices were recorded during the surveyed period which included two times (1.39%), three times (12.5%), four times (30.56%), five times (30.56%) or more than five times (25%). Eighty-nine (89%) of the farmers applied inorganic fertilizer (DAP and urea), whereas 11% did not use fertilizer. Among 144 fields, 92% farmers used improved wheat varieties, while the remaining 8% ignored the use of released varieties. There was only one local variety and 10 improved varieties, namely, Danda’a, Ogolcho, Hidase, Mekuye, Kingbird, Digelu, Shorima, Kakaba’a, Simba and Triticale (Table 1).
3.2. Distribution, Incidence and Severity of FHB of Wheat
Three-stage nested analysis results showed that there was significant (p < 0.05) variation in FHB disease incidence by districts within zones. Significant (p < 0.05) variation was supported by FHB incidence and highly significant variation (at p < 0.01) by severity in PAs nested within the districts and districts within zones, respectively. The overall estimation indicated 55.18% FHB severity index and 78.98% FHB incidence as the mean value of 144 fields of wheat (Table 2).
| Source | Degrees of freedom (df) | FHB disease incidence (DI%) | FHB disease severity index (SI%) |
|---|---|---|---|
| Zones | 5 | 4550.84ns | 1471.85ns |
| Dist (zone) | 6 | 1302.21∗∗ | 304.35ns |
| Peasant association (zone × dist) | 24 | 187.36∗∗ | 107.38∗∗∗ |
| Error | 108 | 78.19 | 34.45 |
| Mean | — | 78.98 | 55.18 |
| CV% | — | 11.2 | 10.64 |
- Abbreviations: ANOVA, analysis of variance; ns, not significant.
- aMean squares: −MS dist (zone), MS peasant association (zone × dist) and MS (error) are used as an error term to test zone, dist (zone) and peasant association (zone × dist), respectively.
- ∗∗Significant at p < 0.05.
- ∗∗∗Highly significant at p < 0.01.
Results of the disease intensity of FHB of wheat between districts were compared using Duncan multiple range test (DMRT) (Table 3). The lowest mean values of FHB incidence, 47.4% and 56.03%, were recorded in Endegagn and Wolissso districts, whereas the highest incidences were in Tello (94.2%) and Deddo (91.6%) districts. The lowest mean value of FHB incidence, 47.4% and 56.03%, was recorded from Endegagn and Wolissso districts, whereas the highest incidences were in Tello (94.2%) and Deddo (91.6%) districts. FHB severity ranged from the highest mean value of Deddo (65.44%) and She-Bench (64.11%) to the least mean value of Endegagn (41.62%) and Wolisso district (42.78%) with insignificant difference between both districts (Table 3 and Figure 5).
| Zone | District | Altitude | FHB disease incidence (%) | FHB severity index (%) | |
|---|---|---|---|---|---|
| Range | Average | ||||
| Jimma | Deddo | 2193–2534 | 2366 | 91.58a | 65.44a |
| Mencho | 1862–2110 | 1969 | 89.62ab | 59.06bc | |
| Southwest Shoa | Wolisso | 2119–2207 | 2168 | 56.032e | 42.78f |
| Kersa malema | 1879–1973 | 1940 | 79.87c | 53.49cd | |
| Bunno-Bedelle | Bedelle | 2027–2177 | 2106 | 81.82bc | 53.23cd |
| Gechi | 2027–2110 | 2073 | 68.49d | 46.27ef | |
| Gurage | Soddo | 1898–2312 | 2127 | 70.46d | 51.2de |
| Endegagn | 2506–2618 | 2569 | 47.39f | 41.62f | |
| Kaffa | Adiyo | 2355–2559 | 2480 | 89.76ab | 61.23ab |
| Tello | 2106–2399 | 2242 | 94.23a | 62.33ab | |
| Bench-Maji | She-Bench | 2024–2229 | 2080 | 89.00ab | 64.11ab |
| Goldiya | 1884–2012 | 1947 | 89.43ab | 61.36ab | |
| CV% | — | — | 12.54 | 12.52 | |
- Note: Means with the same lowercase superscript letters are not significantly different.
3.3. Agronomic Practices in Relation to the Distribution and Intensity of FHB in Wheat
All assessed wheat fields were infected with FHB at different rates. The mean disease severity ranged from 41.62% to 65.44% and the mean incidence from 47.39% to 94.23%. The highest mean disease incidence of 94.23% was recorded at Tello, followed by all the surveyed districts in Jimma, Kaffa and Bench-Maji Zones, while the lowest mean disease incidence of 47.39% was recorded in Endegagn district. Similarly, the highest mean disease severity of 65.44% was recorded in Deddo district, followed by all the surveyed districts in Kaffa and Bench-Maji zones. Contrary, the lowest disease severity of 41.62% was recorded in Endegagn district of Gurage Zone followed by Wolisso (42.78%) and Gechi (46.27%) districts in Southwest Shoa and Buno-Bedelle Zones, respectively (Table 3). Wheat fields with higher FHB incidence (83.73%) and severity (57.12%) were found at altitudes below 2000 m.a.s.l, whereas the lowest incidence (59.93%) and severity (46.50%) were observed in fields located at altitudes above 2500 m.a.s.l. Among the assessed wheat fields, 92 of them showed a mean value of 80.7% and 56% as incidence and severity, respectively, which were located at an altitude 2001–2500 m.a.s.l. FHB incidences and severity of 59.8%–81.81% and 46.5%–56.3% were recorded in sole cropping comprising monocropping and crop rotation production systems. The fields to which recycled seeds were planted had 84.7% mean FHB incidence and 59.03% FHB severity. The least mean value of 68.11% FHB incidence and 50.5% FHB severity was recorded by wheat fields sourced from private seed enterprises. The highest FHB incidence (91.1%) and severity (61.5%) were obtained in wheat fields sown in early September, whereas the lowest disease intensity was recorded in wheat fields sown in July (Table 4).
| Variable | Variable class | Disease incidence (%) | Disease severity index (%) | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Min | Max | Mean | SE | Min | Max | Mean | SE | ||
| Dst | Deddo | 60.02 | 100 | 91.58 | 0.35 | 51.33 | 73.13 | 65.44 | 0.24 |
| Mencho | 82.26 | 93.38 | 89.62 | 0.30 | 45.75 | 68.62 | 59.06 | 0.21 | |
| Wolisso | 30.26 | 70.71 | 56.03 | 0.34 | 35.16 | 52.47 | 42.78 | 0.24 | |
| Kersa Malema | 62.17 | 94.85 | 79.87 | 0.32 | 41.21 | 64.33 | 53.49 | 0.23 | |
| Bedelle | 51.92 | 100 | 81.82 | 0.34 | 33.86 | 66.72 | 53.24 | 0.24 | |
| Gechi | 49.56 | 89.07 | 68.49 | 0.36 | 32.62 | 60.86 | 46.27 | 0.26 | |
| Soddo | 41.00 | 83.09 | 70.46 | 0.38 | 37.56 | 58.37 | 51.198 | 0.28 | |
| Endegagn | 31.24 | 68.16 | 47.39 | 0.39 | 30.56 | 56.72 | 41.62 | 0.27 | |
| Adiyo | 85.51 | 100 | 89.76 | 0.35 | 52.8 | 72.15 | 61.22 | 0.24 | |
| Tello | 80.38 | 100 | 94.26 | 0.39 | 55.37 | 70.66 | 62.33 | 0.26 | |
| She-Bench | 67.63 | 97.88 | 89.00 | 0.31 | 47.21 | 73.18 | 64.11 | 0.21 | |
| Goldiya | 83.33 | 95.66 | 89.43 | — | 55.27 | 70.03 | 61.36 | — | |
| Alt | <2000 | 62.07 | 100 | 83.73 | 0.24 | 41.21 | 70.03 | 57.12 | 0.16 |
| 2001–2500 | 30.25 | 100 | 80.69 | 0.20 | 32.62 | 73.18 | 55.94 | 0.12 | |
| ≥2500 | 31.25 | 96.16 | 59.93 | — | 30.56 | 69.9 | 46.5 | — | |
| LSS | Yes | 30.26 | 100 | 73.25 | 0.16 | 30.56 | 72.15 | 52.15 | 0.13 |
| No | 38.61 | 100 | 85.11 | 0.17 | 32.15 | 73.18 | 58.46 | 0.14 | |
| Yes, but not after FHB information | 47.99 | 100 | 65.94 | — | 35.53 | 70.66 | 47.61 | — | |
| PS | Monocropping | 35.96 | 94.85 | 59.85 | 0.11 | 32.15 | 58.99 | 46.49 | 0.09 |
| Shifting cultivation | 31.25 | 100 | 78.5 | 0.09 | 30.56 | 72.15 | 55.42 | 0.06 | |
| Mixed cropping | 58.77 | 94.99 | 83.72 | 0.11 | 41.4 | 71.02 | 57.36 | 0.08 | |
| Crop rotation | 30.26 | 100 | 81.81 | — | 32.13 | 73.18 | 56.27 | — | |
| SS | Private seed enterprises | 38.61 | 100 | 68.11 | 0.12 | 32.13 | 70.66 | 50.5 | 0.10 |
| Individual farmers | 49.5 | 100 | 73.95 | 0.12 | 32.62 | 66.72 | 50.12 | 0.09 | |
| Farmers cooperatives/union | 31.25 | 100 | 76.8 | 0.08 | 30.56 | 71.02 | 53.32 | 0.06 | |
| Own seeds | 58.41 | 100 | 84.78 | 0.16 | 43.18 | 73.13 | 59.03 | 0.11 | |
| Government or NGO | 30.26 | 100 | 83.24 | — | 35.16 | 73.19 | 58.54 | — | |
| TS | June 19 (earlier) | 49.5 | 94.75 | 74.41 | 0.18 | 32.62 | 60.86 | 50.07 | 0.13 |
| July 19 (appropriate) | 31.25 | 100 | 72.15 | 0.14 | 30.56 | 73.13 | 52.99 | 0.09 | |
| August | 41.00 | 100 | 78.93 | 0.12 | 33.86 | 72.15 | 54.7 | 0.09 | |
| September (late) | 76.07 | 100 | 91.1 | 0.13 | 45.75 | 73.18 | 61.5 | 0.08 | |
| Not known | 30.26 | 100 | 80.07 | — | 42.31 | 62.6 | 55.27 | — | |
| MS | Broadcasting | 44.07 | 100 | 84.16 | 0.08 | 32.62 | 73.13 | 57.05 | 0.06 |
| Row seeding | 30.26 | 100 | 76.98 | — | 30.56 | 73.48 | 54.45 | — | |
| CR | Yes, I use | 30.26 | 100 | 80.71 | 0.10 | 32.62 | 73.13 | 55.69 | 0.07 |
| No, I do not use | 31.25 | 100 | 72.66 | — | 30.56 | 73.18 | 53.3 | — | |
| PC | Teff | 30.26 | 96.16 | 75.17 | 0.12 | 41.21 | 70.87 | 52.13 | 0.09 |
| Maize | 61.16 | 97.88 | 86.87 | 0.12 | 44.37 | 73.18 | 60.23 | 0.08 | |
| Potato | 79.22 | 96.41 | 91.13 | 0.20 | 57.56 | 69.3 | 63.62 | 0.13 | |
| Peas | 35.96 | 93.38 | 71.14 | 0.13 | 32.13 | 68.27 | 53.94 | 0.10 | |
| Beans | 41.00 | 100 | 71.85 | 0.09 | 33.86 | 69.98 | 49.88 | 0.07 | |
| Others | 31.25 | 100 | 77.38 | — | 30.56 | 73.13 | 53.77 | — | |
| MW | Hand weeding only | 30.26 | 95.43 | 77.02 | 0.10 | 35.16 | 71.02 | 53.9 | 0.08 |
| Herbicide only | 44.07 | 100 | 83.06 | 0.12 | 32.62 | 73.18 | 56.71 | 0.09 | |
| Both | 31.24 | 100 | 75.93 | — | 30.56 | 73.13 | 54.32 | — | |
| FW | Thrice | 35.96 | 97.88 | 72.28 | 0.11 | 35.53 | 71.14 | 57.31 | 0.08 |
| Four times | 44.30 | 100 | 83.61 | 0.08 | 32.62 | 73.18 | 56.83 | 0.07 | |
| More than four times | 0.23 | 100 | 75.39 | — | 30.56 | 73.29 | 53.14 | — | |
| FP | Twice | 88.23 | 90.76 | 89.49 | 0.31 | 45.75 | 58.09 | 51.92 | 0.20 |
| Thrice | 31.25 | 100 | 83.11 | 0.17 | 30.56 | 73.13 | 58.00 | 0.12 | |
| Four times | 44.07 | 100 | 81.44 | 0.11 | 34.56 | 73.18 | 56.9 | 0.08 | |
| Five times | 35.96 | 100 | 77.5 | 0.09 | 32.13 | 70.87 | 54.11 | 0.07 | |
| More than five times | 30.26 | 100 | 75.13 | — | 37.33 | 67.67 | 53.15 | — | |
| F | Yes, I use | 30.26 | 100 | 77.58 | 0.19 | 30.56 | 73.18 | 54.54 | 0.12 |
| No, I do not use | 83.33 | 95.66 | 90.14 | — | 52.61 | 70.03 | 60.27 | — | |
| TC | Fungicides | 35.96 | 100 | 81.09 | 0.09 | 32.13 | 73.18 | 57.39 | 0.07 |
| Insecticides | 41.00 | 41.00 | 41.00 | 0.31 | 46.68 | 46.68 | 46.68 | 0.27 | |
| Seed treatment chemicals | 51.15 | 94.75 | 72.63 | 0.13 | 35.16 | 66.72 | 49.3 | 0.11 | |
| No chemicals | 30.26 | 100 | 78.93 | — | 30.57 | 73.13 | 54.77 | — | |
| RVS | Danda’a’ | 49.56 | 97.88 | 80.83 | 0.18 | 32.62 | 73.18 | 55.82 | 0.14 |
| Ogolcho | 30.26 | 94.85 | 65.28 | 0.19 | 37.56 | 58.99 | 48.78 | 0.16 | |
| Hidase | 31.24 | 100 | 81.33 | 0.16 | 30.56 | 70.66 | 54.86 | 0.14 | |
| Mekuye | 35.96 | 96.16 | 70.07 | 0.17 | 32.13 | 70.87 | 53.01 | 0.14 | |
| Kingbird | 86.88 | 100 | 94.83 | 0.30 | 54.9 | 73.13 | 64.97 | 0.19 | |
| Digelu | 58.77 | 100 | 77.26 | 0.20 | 41.21 | 69.3 | 55.35 | 0.16 | |
| Shorima | 47.99 | 95.43 | 80.98 | 0.13 | 33.86 | 72.15 | 55.62 | 0.10 | |
| Kakaba | 41.00 | 84.41 | 74.33 | 0.20 | 46.68 | 58.37 | 53.31 | 0.16 | |
| Triticale | 50.75 | 58.41 | 55.02 | 0.21 | 38.3 | 43.18 | 40.55 | 0.19 | |
| Simba | 83.97 | 95.66 | 90.4 | 0.21 | 56.12 | 70.03 | 62.48 | 0.14 | |
| Local | 52.5 | 100 | 81.68 | — | 43.69 | 69.98 | 57.86 | — | |
- Abbreviations: Alt, altitude; CR, crop rotation; Dst, district; F, fertilizer application; FP, frequency of ploughing; FW, frequency of weeding; LSS, recycling seeds; MS, method of sowing; MW, method of weeding; PC, previous crops; PS, production system; RVS, recent varieties sown; SS, seed source; TC, types of chemicals; TS, time of sowing.
Farmers use various crops before wheat cultivation. The highest mean incidence and severity was recorded by potato before wheat with the mean value of 91.13% and 63.62%. Similarly, disease incidence and severity of 86.87% and 60.23% were recorded by maize planted before wheat, respectively. Contrary, the lowest disease intensity value was recorded in fields with pea and beans as previous crops. Results of this study showed that ploughing two times had the highest proportion (89.49%) of infected fields but the lowest percentage (51.92%) of severely infected fields. Relatively lower incidence and severity of FHB, 75.13%–77.5% and 53.15%–54.11%, respectively, were obtained on fields ploughed five or more times. Contrary to those fields that mineral fertilizer was applied, wheat fields without fertilizer application showed higher 90.14% FHB incidence and 60.27% severity. Wheat fields showed different responses to cultivars under natural conditions for FHB infection.
Higher estimate of 94.83% FHB incidence and 64.97% severity of FHB were recorded for Kingbird variety, followed by Simba with 90.4% incidence and 62.5% severity. The lowest incidence (55%) and severity (40.55%) of FHB were recorded in triticale wheat cultivars followed by 65.3% incidence and 48.8% severity in Ogolcho cultivars (Table 4 and Figure 6).
3.4. Association Between Epidemics of FHB and Agronomic Practices
The relationships between agronomic practices and some biophysical factors with the FHB intensity of wheat are presented in Table 5. All independent variables showed a highly significant association with the incidence and severity of FHB when entered first into the model for logistic regression analysis.
| Independent variables | df | FHB incidence, LRT | FHB severity, LRT | ||||||
|---|---|---|---|---|---|---|---|---|---|
| Type I analysis (VEF) | Type III analysis (VEL) | Type I analysis (VEF) | Type III analysis (VEL) | ||||||
| DR | Pr > χ2 | DR | Pr > χ2 | DR | Pr > χ2 | DR | Pr > χ2 | ||
| Intercept | — | 2685.64 | — | 2685.64 | <0.0001 | 634.20 | — | 634.20 | — |
| Dst | 11 | 1754.53 | <0.0001 | 1754.03 | <0.0001 | 372.63 | <0.0001 | 372.63 | <0.0001 |
| Alt | 2 | 383.73 | <0.0001 | 0.75 | 0.69 | 42.49 | <0.0001 | 1.65 | 0.44 |
| LSS | 2 | 339.64 | <0.0001 | 16.90 | 0.0002 | 65.78 | <0.0001 | 0.5 | 0.78 |
| PS | 3 | 345.01 | <0.0001 | 13.12 | 0.0044 | 52.49 | <0.0001 | 3.63 | 0.30 |
| SS | 4 | 200.23 | <0.0001 | 3.34 | 0.5030 | 70.77 | <0.0001 | 6.18 | 0.19 |
| TS | 4 | 488.89 | <0.0001 | 39.69 | <0.0001 | 78.62 | <0.0001 | 15.45 | 0.004 |
| MS | 1 | 93.68 | <0.0001 | 1.08 | 0.3132 | 7.90 | 0.0049 | 1.04 | 0.31 |
| CR | 1 | 90.59 | <0.0001 | 1.36 | 0.2436 | 5.63 | 0.0177 | 0.81 | 0.37 |
| PC | 5 | 373.99 | <0.0001 | 72.11 | <0.0001 | 101.56 | <0.0001 | 22.65 | 0.0004 |
| MW | 2 | 97.73 | <0.0001 | 4.19 | 0.1231 | 9.10 | 0.0105 | 2.31 | 0.31 |
| FW | 2 | 168.92 | <0.0001 | 12.53 | 0.0019 | 20.41 | <0.0001 | 1.42 | 0.49 |
| FP | 4 | 88.32 | <0.0001 | 14.61 | 0.0056 | 20.00 | 0.0005 | 10.86 | 0.03 |
| F | 1 | 157.14 | <0.0001 | 14.88 | 0.0001 | 19.06 | <0.0001 | 0.08 | 0.78 |
| TC | 3 | 92.19 | <0.0001 | 50.35 | <0.0001 | 19.41 | 0.0002 | 7.84 | 0.05 |
| RVS | 10 | 448.02 | <0.0001 | 107.68 | <0.0001 | 90.14 | <0.0001 | 22.44 | 0.01 |
- Note: χ2, chi-square; Pr, probability of an χ2 exceeding the deviance reduction.
- Abbreviations: df, degrees of freedom; DR, deviance reduction; LRT, likelihood ratio test; VEF, variable entered first; VEL, variable entered last.
However, altitude, seed source, method of sowing, crop rotation and method of weeding lost their importance with respect to FHB incidence when they were entered last into the model. Regarding the severity of FHB, most of the variables lost their importance when entered last into the model except district, time of sowing, previous crops, recently sown varieties and frequency of tillage (Table 5). Those significant variables were tested in a reduced regression model and analysis of deviance by adding them one by one into the model to show the importance of each variable. The parameter estimates were computed for further analysis of odds ratio indicating associations of important independent variables with FHB incidence and severity.
The high FHB incidence (≥75%) was significantly associated with Tello, She-Bench, Mencho and Adiyo districts; sowing from August to September; potato, maize and teff as a preceding crop; four times ploughing frequency; and Kingbird, Kakaba’a’ and Mekuye as a recently sown wheat variety. Low incidence (<75%) of FHB had high probability of association with Endegagn, Soddo, Gechi and Wolisso districts; planting in July; three times weeding frequency; peas and beans as preceding crops; and Triticale, Shorima and Hidase as a recently sown wheat variety (Table 6).
| Added variable | Residual deviancea | df | FHB incidence LRTb | Variable class | Estimate loge (odds ratio)c | SE | Odds ratio | |
|---|---|---|---|---|---|---|---|---|
| DR | Pr > χ2 | |||||||
| Intercept | 2685.64 | 182.45 | <0.0001 | — | 2.95 | 0.12 | 19.06 | |
| Dst | 931.09 | 11 | 4.16 | 0.0414 | Deddo | −0.26 | 0.31 | 0.77 |
| 51.92 | <0.0001 | Mencho | 0.57 | 0.27 | 1.77 | |||
| 67.16 | <0.0001 | Wolisso | −1.55 | 0.31 | 0.21 | |||
| 1.73 | 0.1889 | Kersa Malema | −0.73 | 0.30 | 0.48 | |||
| 20.35 | <0.0001 | Bedelle | −1.04 | 0.31 | 0.35 | |||
| 77.59 | <0.0001 | Gechi | −1.71 | 0.31 | 0.18 | |||
| 18.33 | <0.0001 | Soddo | −1.30 | 0.36 | 0.27 | |||
| 250.95 | <0.0001 | Endegagn | −2.36 | 0.29 | 0.09 | |||
| 27.97 | <0.0001 | Adiyo | 0.15 | 0.29 | 1.16 | |||
| 93.59 | <0.0001 | Tello | 1.25 | 0.34 | 3.51 | |||
| 29.70 | <0.0001 | She-Bench | 0.32 | 0.27 | 1.37 | |||
| — | — | Goldiya | — | — | — | |||
| LSS | 913.53 | 2 | 15.79 | <0.0001 | Yes | −0.51 | 0.15 | 0.60 |
| 2.102 | 0.1471 | No | −0.39 | 0.16 | 0.67 | |||
| — | — | Yes, but not after FHB information | — | — | — | |||
| PS | 900.55 | 3 | 2.504 | 0.1135 | Monocropping | −0.01 | 0.11 | 1.01 |
| 8.14 | 0.0043 | Shifting cultivation | −0.28 | 0.08 | 0.76 | |||
| 0.894 | 0.3445 | Mixed cropping | −0.19 | 0.10 | 0.83 | |||
| — | — | Crop rotation | — | — | — | |||
| TS | 835.02 | 4 | 10.36 | 0.0013 | June | 0.92 | 0.16 | 2.5 |
| 22.39 | <0.0001 | July | 0.89 | 0.13 | 2.44 | |||
| 22.19 | <0.0001 | August | 0.88 | 0.12 | 2.41 | |||
| 8.77 | 0.0031 | September | 0.33 | 0.12 | 1.40 | |||
| — | — | Not known | — | — | — | |||
| PC | 796.58 | 5 | 0.3814 | 0.5369 | Teff | −0.09 | 0.11 | 0.91 |
| 1.92 | 0.1664 | Maize | −0.16 | 0.12 | 0.85 | |||
| 32.8 | <0.0001 | Potato | 0.81 | 0.18 | 2.24 | |||
| 23.99 | <0.0001 | Peas | −0.49 | 0.12 | 0.61 | |||
| 14.65 | 0.0001 | Beans | −0.32 | 0.08 | 0.73 | |||
| — | — | Others | — | — | — | |||
| FW | 783.22 | 2 | 4.51 | 0.0336 | Thrice | −0.20 | 0.10 | 0.82 |
| 3.14 | 0.0762 | Four times | 0.02 | 0.06 | 1.02 | |||
| — | — | More than four times | — | — | — | |||
| FP | 762.87 | 4 | 0.0041 | 0.8404 | Twice | −0.14 | 0.30 | 0.87 |
| 10.14 | 0.0014 | Three times | −0.50 | 0.14 | 0.60 | |||
| 3.57 | 0.0587 | Four times | −0.04 | 0.10 | 0.96 | |||
| 0.348 | 0.5553 | Five times | −0.23 | 0.08 | 0.79 | |||
| — | — | More than five times | — | — | — | |||
| F | 750.53 | 1 | 7.58 | 0.0059 | Yes, I use | −0.48 | 0.17 | 0.62 |
| — | — | No, I do not use | — | — | — | |||
| TC | 711.84 | 3 | 13.98 | 0.0002 | Fungicides | −0.26 | 0.09 | 0.77 |
| 32.87 | <0.0001 | Insecticides | −1.78 | 0.27 | 0.17 | |||
| 3.49 | 0.0617 | Seed treat chemicals | −0.39 | 0.12 | 0.68 | |||
| — | — | No chemicals | — | — | — | |||
| RVS | 615.84 | 10 | 1.465 | 0.2262 | Danda’a’ | −0.02 | 0.17 | 0.98 |
| 21.66 | <0.0001 | Ogolcho | −0.68 | 0.18 | 0.50 | |||
| 3.89 | 0.0485 | Hidase | −0.33 | 0.15 | 0.71 | |||
| 3.75 | 0.0529 | Mekuye | −0.05 | 0.16 | 1.05 | |||
| 24.81 | <0.0001 | Kingbird | 1.00 | 0.28 | 2.72 | |||
| 8.51 | 0.0035 | Digelu | −0.48 | 0.18 | 0.62 | |||
| 7.20 | 0.0073 | Shorima | −0.44 | 0.13 | 0.64 | |||
| 5.94 | 0.0148 | Kakaba | 0.18 | 0.19 | 1.20 | |||
| 23.95 | <0.0001 | Triticale | −0.90 | 0.20 | 0.41 | |||
| 0.47 | 0.493 | Simba | −0.01 | 0.20 | 0.99 | |||
| — | — | Local | — | — | — | |||
- Note: χ2, chi-square; Pr, probability of an χ2 exceeding the deviance reduction.
- Abbreviations: df, degrees of freedom; DR, deviance reduction; Dst, district; F, fertilizer application; FP, frequency of ploughing; FW, frequency of weeding; LRT, likelihood ratio test; LSS, recycling seeds; PC, previous crops; PS, production system; RVS, recent varieties sown; TC, types of chemicals; TS, time of sowing.
- aUnexplained variations after fitting the model.
- bLRT.
- cReference group.
In the reduced regression model, it has been observed that high FHB severity (≥55%) had high probability of association with Telo, Mencho, She-Bench and Adiyo districts; potato, teff and maize as previous crops; four times ploughing frequency; and Kakaba’a’, Kingbird and Mekuye as a recently sown wheat varieties. Equally, low severity (<55%) of FHB was significantly associated with Endegagn, Soddo, Gechi and Wolisso districts, sowing from late June to July, fertilizer application, three times weeding frequency, peas and beans as a previous crop, four times ploughing frequency, three times weeding frequency and Triticale, Shorima and Hidase as a recently sown wheat variety (Table 7).
| Added variable | Residual deviancea | df | Fusarium head blight severity index LRTb | Variable class | Estimate loge (odds ratio)c | SE | Odds ratio | |
|---|---|---|---|---|---|---|---|---|
| DR | Pr > χ2 | |||||||
| Intercept | 634.20 | 11.67 | 0.0007 | — | 0.53 | 0.22 | 1.70 | |
| Dst | 261.57 | 11 | 4.75 | 0.0293 | Deddo | −0.144 | 0.192 | 0.866 |
| 18.23 | <0.0001 | Mencho | −0.064 | 0.163 | 1.066 | |||
| 19.82 | <0.0001 | Wolisso | −0.757 | 0.197 | 0.469 | |||
| 5.72 | 0.0168 | Kersa Malema | −0.583 | 0.185 | 0.558 | |||
| 5.26 | 0.0218 | Bedelle | −0.526 | 0.193 | 0.591 | |||
| 23.81 | <0.0001 | Gechi | −0.777 | 0.199 | 0.460 | |||
| 13.04 | 0.0003 | Soddo | −0.790 | 0.223 | 0.454 | |||
| 64.77 | <0.0001 | Endegagn | −0.968 | 0.170 | 0.380 | |||
| 16.30 | <0.0001 | Adiyo | 0.033 | 0.162 | 1.033 | |||
| 22.05 | <0.0001 | Tello | 0.165 | 0.199 | 1.179 | |||
| 19.46 | <0.0001 | She-Bench | 0.092 | 0.162 | 1.096 | |||
| — | — | Goldiya | — | — | — | |||
| TS | 247.61 | 4 | 1.07 | 0.3009 | June | 0.310 | 0.113 | 1.364 |
| 11.24 | 0.0008 | July | 0.378 | 0.086 | 1.460 | |||
| 2.71 | 0.0994 | August | 0.311 | 0.083 | 1.365 | |||
| 0.728 | 0.3937 | September | 0.189 | 0.076 | 1.208 | |||
| — | — | Not known | — | — | — | |||
| PC | 221.47 | 5 | 0.1283 | 0.7202 | Teff | 0.019 | 0.080 | 1.020 |
| 0.0514 | 0.8207 | Maize | 0.054 | 0.080 | 1.056 | |||
| 9.46 | 0.0021 | Potato | 0.307 | 0.110 | 1.359 | |||
| 0.5139 | 0.4734 | Peas | −0.005 | 0.084 | 0.995 | |||
| 12.03 | 0.0005 | Beans | −0.132 | 0.059 | 0.877 | |||
| — | — | Others | — | — | — | |||
| FP | 210.49 | 4 | 3.5 | 0.0613 | Twice | −0.423 | 0.192 | 0.655 |
| 0.3331 | 0.5639 | Thrice | −0.195 | 0.098 | 0.823 | |||
| 4.41 | 0.0357 | Four times | −0.059 | 0.073 | 0.943 | |||
| 0.785 | 0.3756 | Five times | −0.11 | 0.061 | 0.896 | |||
| — | — | More than five times | — | — | — | |||
| RVS | 189.17 | 10 | 0.104 | 0.747 | Danda’a’ | −0.036 | 0.124 | 0.965 |
| 0.271 | 0.603 | Ogolcho | 0.036 | 0.146 | 1.037 | |||
| 4.07 | 0.044 | Hidase | −0.155 | 0.119 | 0.856 | |||
| 2.62 | 0.106 | Mekuye | 0.108 | 0.122 | 1.114 | |||
| 1.67 | 0.196 | Kingbird | 0.150 | 0.169 | 1.162 | |||
| 0.155 | 0.694 | Digelu | 0.023 | 0.143 | 1.023 | |||
| 6.65 | 0.009 | Shorima | −0.211 | 0.093 | 0.810 | |||
| 5.56 | 0.018 | Kakaba | 0.230 | 0.154 | 1.259 | |||
| 4.14 | 0.042 | Triticale | −0.282 | 0.175 | 0.754 | |||
| 0.011 | 0.916 | Simba | 0.002 | 0.18 | 1.002 | |||
| — | — | Local | — | — | — | |||
- Note: χ2, chi-square; Pr, probability of an χ2 exceeding the deviance reduction.
- Abbreviations: df, degrees of freedom; DR, deviance reduction; Dst, districts; FP, frequency of ploughing; LRT, likelihood ratio test; PC, previous crops; RVS, recent varieties sown; TS, time of sowing.
- aUnexplained variations after fitting the model.
- bLRT.
- cReference group.
4. Discussion
FHB of wheat was found throughout the surveyed fields, with mean incidence and severity ranging from 47.39% to 94.23% and 41.62%–65.44%, respectively. The epidemic of FHB was low or moderate in districts assessed from Central Ethiopia. It was more severe and widely distributed in districts sampled in Southwest Ethiopia (Tables 1 and 3). As reported by Abdissa and Bekele [34], the mean FHB incidence and severity index across the assessed surveyed districts were 43.7% and 76.3%, respectively. Our results are consistent with those of other authors who found the FHB incidence and severity of 22.28%−53.35% and 16.57%−37.73% [19] and 0%–100% and 12.3%–30.1% [22], respectively, in the same location. This may be attributed to the difference in agroecology, resulting in weather variations among the districts. In our study, most of the wheat fields with both the lowest and highest FHB intensities were found in districts at altitudes ranging from 1862 to 2618 m.a.s.l., with the lowest FHB intensity found in the Endegagn district at altitudes above 2500 m.a.s.l., which constituted 17 wheat fields. Nevertheless, 63.88% of the fields which were located at 2001–2500 m.a.s.l. which indicated 80.69% and 55.94% FHB disease incidence and severity, respectively (Tables 1 and 4). Based on our results, the study suggests that the disease intensity decreases with a continuous increase in altitude, although further research is proposed. The range of altitude in this study is similar to that of Muluken et al. [23], who reported that FHB intensity was higher in areas with an altitude ranging from 1773 to 2332 ma.s.l.
In this study, the majority of the fields with greater FHB disease intensity were situated in the Bench-Maji and Jimma Zones of Southwest Ethiopia. The average rainfall and temperature in the major wheat growing season ranged from 128 to 215 mm and 19 to 24°C (Figures 2 and 3). The temperature and precipitation range of these areas are favourable for FHB infections. This result is similar with other findings, which reported that high incidence was attributed to favourable weather conditions for FHB, which consists of high precipitation (114–150 mm) and a temperature range of 12.55–28.5°C [23, 41]. Parry et al. [42] also explained that rainy weather can encourage the dispersal of ascospores, thus resulting in FHB infections. Their study further highlighted the necessity of dry periods as the necessary conditions for the forceful discharge of ascospores into the atmosphere, although the rain or heavy dew are a prerequisite for the initial release of ascospores.
In our assessment, FHB intensity was high in areas under humid weather and most notably in the following districts of Southwest Ethiopia, namely, Deddo, Tello and She-Bench. Our results are supported by the higher relative humidity ranging from 60% to 70% during the growing season as indicated in Figure 4. FHB is more prevalent in areas with hot and humid weather supported by high relative humidity for at least 12 h and when the temperature is between 24 and 29°C [43]. The temperature range in our study was below the lower limit for FHB development. However, a study by Wise et al. [44] reported that the disease can occur at lower temperatures in the presence of prolonged periods of high humidity and moisture. It has been observed that FHB disease is influenced by the timing of moisture during the wheat growth stage. Lori et al. [45] reported that abundant moisture at the heading stage has a significant influence on disease development. Several other studies, reported differences in agroecology across locations, have a considerable year-to-year variability in FHB intensity [27, 46].
Previous cropping history has been reported to influence the intensity of FHB in wheat, as was also the case in our study, where FHB intensity was more severe when wheat was grown after maize, potato and teff. These finding agrees with those reported by Inch and Gilbert [47], which indicated that the inoculum of G. zeae survived for extended periods of time on plant debris. Maize, as a previous crop, has been reported to induce severe FHB epidemics [48–51]. Potato as an alternate host of F. graminearum has also been reported by Tiwari et al. [52] and Xue et al. [53], which is in line with our results. The study obtained a lower intensity of FHB when wheat was grown after peas and beans (Table 4). This was also supported by the strong and negative association of low FHB intensity with peas and beans (Tables 6 and 7), suggesting their relative importance in reducing FHB epidemics. In support of our study, growing nonhosts and more notably soybean and faba beans as a previous crop were reported to reduce FHB epidemics [13, 23, 42, 54].
This study also revealed the significance of planting time in relation to controlling the FHB epidemic. In the current study, the intensity of FHB was more severe when wheat was planted late in September but was suppressed when it was sown late June to July (Table 4). Planting time had a high probability of being associated with both high and low FHB incidence (Tables 6 and 7), signalling its relative importance in both inducing and reducing disease epidemics. Our results align with those of several authors, who reported that late sowing favoured the development of FHB [9, 23]. Our results are inconsistent with other authors who concluded that sowing date has no critical influence on FHB epidemics [41] and those who found high levels of FHB incidence at early planting time [55].
Tillage practices were recognized as a means of reducing the FHB epidemic. In our study, wheat fields ploughed twice before sowing resulted in the highest incidence of FHB, followed by three to four ploughings, while fields ploughed five or more times had the lowest percentage of infection (Table 4). Thus, the less incidence (<75%) and severity (<55%) were highly associated with more frequent ploughing (Tables 6 and 7), indicating that disease intensity increased as the frequency of ploughing decreased. This result is in agreement with previous studies [23, 54, 56, 57], in which disease epidemics were associated with tillage practices. In relation to fertilizer application, the intensity of FHB was more severe in unfertilized fields but was relatively suppressed when fertilizer was applied (Table 4). Similarly, to our findings, Veresoglou et al. [58] reported that optimal fertility of any crop reduces plant stress, improves physiological resistance and decreases disease risks.
The disease intensity response of FHB differs among the recently grown wheat varieties. In our study, high incidence (94.83%) and severity (64.97%) were recorded by the kingbird cultivar, followed by 90.4% and 62.48% for Simba. Low incidence and severity of FHB were registered by Triticale and Ogolcho cultivars (Table 4). Both high and low FHB incidences in the present study showed a significant association with recently grown wheat varieties (Tables 6 and 7). This suggests that this variable contributed significantly to both the decrease and the induction of FHB epidemics. In support of this result, different levels of response to the FHB epidemic have been observed among wheat cultivars grown in Ethiopia [19, 23, 34, 59]. Similar differences are also evident among wheat varieties grown in different parts of the world [54, 55, 60, 61]. The difference in the response of recently grown wheat varieties to FHB may be due to the variation in genetic makeup of the varieties or partly to the genotype-by-environment interaction effect.
5. Conclusion
In the present study, the incidence and severity of FHB varied significantly among the surveyed districts. Among others, Tello, Deddo, Adiyo, She-Bench and Goldiya districts in Southwest Ethiopia had the highest number of severely infected fields. In contrast, the Endegagn district in the Gurage Zone had the lowest proportion of infections and severely infected fields. The results confirmed that FHB disease is severe in Southwest Ethiopia but comparatively less so in Central Ethiopia.
This study demonstrates that agronomic practices affect the relative intensity of FHB in wheat. Less frequent ploughing and late planting from August to September strongly favoured the development of FHB in wheat. Similarly, the disease intensity of FHB was more severe when wheat was grown after maize, potatoes and teff.
We conclude that five or more times ploughing, peas and beans as previous crops and planting wheat from late June to July could be used as management options to reduce severe FHB epidemics. The level of genetic resistance to FHB differs among recently grown wheat varieties on individual farms as both the earlier and recently released varieties, Simba and Kingbird, which were released in 2000 and 2015, respectively, showed a high intensity of FHB. However, Triticale, Hidase and Shorima were less likely to be infected with FHB. Future research may thus focus on less infected wheat varieties that make the largest contribution to the crop improvement against FHB infection in wheat, along with appropriate agronomic practices.
Disclosure
The funder has no role in writing, editing, approval or decision in publication of this work.
Conflicts of Interest
The authors declare no conflicts of interest.
Funding
This study was funded by the Ministry of Education, Ethiopia, as part of an employment for researcher and lecturer in Wolkite University.
Acknowledgments
The authors acknowledge the Ministry of Education, Ethiopia, for financing this research work. Special thanks are due to Jimma University College of Agriculture and Veterinary Medicine for administering the budget, overseeing the whole laboratory activities and fieldwork in Illadale and providing general support to carry out the authors’ work. The authors also thank, especially, those extension staff members of the surveyed districts for their collaboration in transport services and the development agents in agriculture and rural development offices for their cooperation during the assessment. Great thanks are due to all the farmers in the study areas who allowed the authors to take wheat samples from their fields to conduct further laboratory experiments.
Open Research
Data Availability Statement
The data that support the findings of this study are available from the corresponding author upon reasonable request.
