ACADEMIA Letters A case report on Cercospora leaf spot (Cercospora sesami zimm.) disease occurrence in the mid and lowland sesame growing districts of Bale zone, South-east Oromia, Ethiopia Ermias Teshome, Sinana Agricultural Research Center Dagne Kora, Sinana Agricultural Research Center Temam Hasen, Goba Plant Health Clinic Habtamu Merga, Bale Zone Agricultural Office Abstract Sesame (Sesamum indicum) is a vital oil crop produced in the tropical and subtropical parts of the World. Ethiopia is one of the major sesame producer countries. The crop was newly introduced into the mid and lowland districts of the Bale zone. Berbere, Harana-buluk, Medewolabu and Delo-mena were among the districts in which the crop has penetrated very fast. With the fast expansion of the crop in these areas, some sesame diseases were also occurring and challenging the productivity of the crop. As a result, farmers of these districts have reported the problem to districts and zonal agricultural offices and Sinana Agricultural Research Center (SARC) repeatedly. In response to the queries from farmers, the zonal agricultural office and SARC have established a multidisciplinary team consisting of four (4) experts. The team has traveled to the representative districts and assessed the farms at every 3-4km stop depending on the availability of the crop. A series of discussions were held with farmers, development agents, and agricultural office experts to create awareness about the problem, and advice was also given on the immediate solution. Based on the field symptoms manifested by Academia Letters, January 2022 ©2022 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: Ermias Teshome, ermiastafa@gmail.com Citation: Teshome, E., Kora, D., Hasen, T., Merga, H. (2022). A case report on Cercospora leaf spot (Cercospora sesami zimm.) disease occurrence in the mid and lowland sesame growing districts of Bale zone, South-east Oromia, Ethiopia. Academia Letters, Article 4564. https://doi.org/10.20935/AL4564. 1 the disease, the team has suspected that the main cause of the problem was to be Cercospora leaf spot (Cercospora sesami Zimm.) which is one among the major sesame diseases. Finally, the disease was identified at the SARC’s plant pathology laboratory and the cause was confirmed to be Cercospora leaf spot of sesame. for its management, different fungicides were screened by SARC. Among the screened fungicides, Tilt 250 EC was found effective in controlling the disease and recommended for users. The article for the fungicides screening work is published (https://doi.org/10.33545/27080013.2021.v2.i1b.34). Introduction Sesame (Sesamum indicum) is one of the important oil crops produced in the tropical and subtropical parts of the World (Kavak, 2006). Ethiopia is one of the major sesame-producing countries and contributes to the world’s sesame market. Out of the total land allocated for crop production, 375,119.95 ha of land was allocated to sesame production from which about 262,654.2 tonnes of sesame grains were harvested (CSA, 2020). The sesame seeds are rich in oil (50 to 52%), protein (17 to 19%), and carbohydrates (16 to 18%). Sesame seeds and oil are highly in demand in the world because of their high unsaturated fat and methionine contents (Schilling and Catan, 1991; Uzoh, 1998). Leaf spot disease caused by Cercospora sesami Zimm., however, is a major problem in the cultivation of this crop, as this disease is prevalent in most sesame growing areas of the world (Uwala, 1998). The disease, which damages the stems and the leaves of sesame, occurs as early as four weeks after planting. Cercospora leaf spot infects all above-ground parts of the plant. The fungus is responsible for leaf spots that affect, especially, the older leaves. First appears on the leaves as minute water-soaked lesions, which enlarge to form round to irregular spots. The spots coalesce to form irregular patches of varying size leading to premature defoliation of leaves which leads to severe economic losses (da Paz-Lima et al., 2017). It can cause yield losses ranging from 22 to 53% (Enikuomehin et al., 2002). The infection is also seen on stem and petiole forming spots of varying lengths. Dark linear spots also occur on pods causing drying shedding. During the hot and rainy season, temperatures above 25 °C and air humidity above 90% become ideal for are growth and development of the pathogen (Amorim et al., 2011). The fungus can survive in the seeds and on the foliar surface of several for a long time until conditions favorable to cause infection (Custodio, 2011). The Cercospora sesami spores germinate in humid conditions. The spores spread to healthy plants through rain, irrigation water, and wind. Fungus growth is encouraged when leaves are frequently wet (Londase, 2013). The hyphae of Cercospora sesame is irregularly septate, light brown, and thick-walled. Conidiophores are produced in clusters, hyaline at the tip and light brown colored at the base. Conidia are elongated; 7-10 Academia Letters, January 2022 ©2022 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: Ermias Teshome, ermiastafa@gmail.com Citation: Teshome, E., Kora, D., Hasen, T., Merga, H. (2022). A case report on Cercospora leaf spot (Cercospora sesami zimm.) disease occurrence in the mid and lowland sesame growing districts of Bale zone, South-east Oromia, Ethiopia. Academia Letters, Article 4564. https://doi.org/10.20935/AL4564. 2 septate, hyaline to light yellow, broad at the base, and tapering towards the apex. Methodology The survey was conducted by an experts group of four (4) individuals organized from SARC, Arsi-Bale Plant Health Clinic, and Bale Zone Agricultural Office. The survey was conducted in 2014/15 cropping season in some selected districts of the low and mid-altitude of Bale zone. Harena-buluk, Delo-mena and Mede-wolabu districts were the main target areas of the survey where the team has assessed the farms. The survey route was from Harena-buluk through Delo-mena to Mede-wolabu. The assessment was done at every 3-4 km stop using the car speedometer which has helped us gather precise information representative to the surveyed districts throughout the whole survey routes as long as the crop has existed. The disease data was recorded on the base of individual plants from five (5) points by walking across the farm in a “W” fashion. The cercospora leaf spot was rated according to 1-7 scoring scale (Enikuomehin, 2005). The disease collected on scale base was then converted to Percent Severity Index (PSI) (Wheeler, 1969). Results Sesame production has a very short history which may not exceed more than 5-6 years in the mid and lowlands of Bale. However, within these short years, its production is expanding tremendously and the potential of sesame in these districts was very high. Particularly, in districts like Harena-buluk, Delo-mena, and Mede-wolabu, the farming system was completely changing to a sesame mono-cropping system when this assessment was done. It was observed that except for very few farms which were planted with teff and maize, totally the farmlands were occupied by sesame during the survey. As a result, leaf spot diseases (Cercospora leaf spot and Bacterial blight) are expanding widely. The outbreak of these diseases was observed widely during the 2013/14 season. Similarly, these diseases occurred in the 2014/15 season in the mentioned districts. The identification of this disease from bacterial leaf spot was not easy. It was tried to identify the disease on the field but it was confirmed at SARC plant pathology after isolation and grown on the culture media. Throughout the surveyed districts, only a few sesame cultivars were observed. Some of these varieties planted on a few farms were improved varieties. However, one cultivar which has dominated the farms in all the districts was unknown. According to the local farmers, it was suspected that this cultivar was introduced to the districts by individual growers from neighboring countries through the border. And the zonal agricultural office was attempting Academia Letters, January 2022 ©2022 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: Ermias Teshome, ermiastafa@gmail.com Citation: Teshome, E., Kora, D., Hasen, T., Merga, H. (2022). A case report on Cercospora leaf spot (Cercospora sesami zimm.) disease occurrence in the mid and lowland sesame growing districts of Bale zone, South-east Oromia, Ethiopia. Academia Letters, Article 4564. https://doi.org/10.20935/AL4564. 3 to replace this unknown cultivar with improved varieties which their adaptation was already tested and recommended by SARC. The survey was conducted focusing on Cercospora leaf spot disease of sesame. According to the finding of this quick assessment, the total farms assessed were infected by the disease and no field was observed being free from the diseases (Table 1). The disease incidence of 100% was scored. The disease severity was found to be in the range of 9% - 20% (Table 1). The highest disease severity 20 %, 13 % and 9% was recorded from Harena buluk, Delo-mena and Mede-wolabu districts, respectively (Table 1). In most cases, this disease was observed to occur at the early seedling growth stage and progressed to a high level at about the flowering stage (Fig. 1A and 1B). In all three districts, only very few farmers (>1%) have been applying fungicides for the management of the diseases because of a lack of awareness about the diseases and the management methods. Figure 1: Symptoms of the disease on the Sesame leaf (A) and Symptom of the disease on the stem of Sesame (B) Table 1: Sesame diseases observed and recorded during the survey in 2014/15 Academia Letters, January 2022 ©2022 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: Ermias Teshome, ermiastafa@gmail.com Citation: Teshome, E., Kora, D., Hasen, T., Merga, H. (2022). A case report on Cercospora leaf spot (Cercospora sesami zimm.) disease occurrence in the mid and lowland sesame growing districts of Bale zone, South-east Oromia, Ethiopia. Academia Letters, Article 4564. https://doi.org/10.20935/AL4564. 4 Actions taken, conclusion and Recommendation As a short-term solution, the team has taken some actions in creating awareness about this alarming sesame disease. At each district, the team has been advising the farmers to give attention to crop diversity and exercise the crop rotation system by inserting pulse crops like Common bean, Mung bean, and Soybean in the cropping system. The farmers were advised to strictly inspect their farmland continuously to monitor the progress of the disease. For an immediate solution, spraying of a fungicide Mancozeb 80% WP at a rate of 2 kg/ha a.i (based lessons learned from 2013/14) was recommended by dissolving in 200-250 L of water during severe cases. For sustainable production of sesame in the area, the assignment of studying the disease and its management strategies was given to SARC. Accordingly, SARC has studied and identified effective fungicide for the management of Cercospora leaf spot and recommendations Tilt 250 EC at a rate of 0.5 l/ha mixed with 200-250 L of water. Regarding the fungicides screening, detailed information can be obtained from the published article which is available on https://doi.org/10.33545/27080013.2021.v2.i1b.34. The team has held two short meetings with the agricultural offices in each district before and after the surveys to create awareness about the problem. The expansion, severity, and progress of the disease were reported to each districts’ agricultural office officers and to the director of the zone office of agriculture. Academia Letters, January 2022 ©2022 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: Ermias Teshome, ermiastafa@gmail.com Citation: Teshome, E., Kora, D., Hasen, T., Merga, H. (2022). A case report on Cercospora leaf spot (Cercospora sesami zimm.) disease occurrence in the mid and lowland sesame growing districts of Bale zone, South-east Oromia, Ethiopia. Academia Letters, Article 4564. https://doi.org/10.20935/AL4564. 5 References Amorim L., Rezende J.A.M.; Filho B., de Fitopatologia A.M., 2011. 4th ed. Piracicaba: Agronômica Ceres. Custódio A.A.P., 2011. Comparison and validation of diagrammatic scales for brown eye spots in coffee tree leaves. Ciência e Agrotecnologia, vol. 35, n. 6, p. 1067-1076. CSA (Central Statistical Authority), 2020. Agricultural sample survey report on area and production of crops (private peasant holdings, meher season). Statistical Bulletin 587. Addis Ababa, Ethiopia. da-Paz-Lima M.L., Decloquement J., Fonseca R.S.A., Lemes, N.M., Neves P.R., Rietjens A.R., Silva J.M., Pereira R. and Junior C., 2017. Identification and frequency analysis of reproductive structures of cercospora sesami incident in gergelim leaves (Sesamum indicum). Gl. 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Academia Letters, January 2022 ©2022 by the authors — Open Access — Distributed under CC BY 4.0 Corresponding Author: Ermias Teshome, ermiastafa@gmail.com Citation: Teshome, E., Kora, D., Hasen, T., Merga, H. (2022). A case report on Cercospora leaf spot (Cercospora sesami zimm.) disease occurrence in the mid and lowland sesame growing districts of Bale zone, South-east Oromia, Ethiopia. Academia Letters, Article 4564. https://doi.org/10.20935/AL4564. 7