East African Journal of Sciences (2019) Volume 13 (2) 135-144 Distribution and Importance of Common Rust of Maize (Puccinia sorghi Schw.) in Hararghe Highlands, Eastern Ethiopia Zelalem Bekeko School of Plant Sciences, Haramaya University, P.O. Box 138, Dire Dawa, Ethiopia Abstract: Maize is an important staple crop in Ethiopia. However, its production is threatened by a number of diseases among which common rust caused by Puccinia sorghi, is the most destructive foliar disease of the crop in the country. Data are useful to gain insight into the occurrence, distribution, relative importance of plant diseases and the association of these diseases with cropping systems, environmental factors and cultural practices. Therefore, field surveys were conducted during 2013 and 2014 main cropping seasons in Hararghe highlands, Ethiopia to investigate the prevalence, intensity and importance of common rust of maize. In both years, a total of 230 maize fields were surveyed in eastern and western Hararghe zones. In order to incorporate different altitudinal ranges and analyze the survey data, a three-stage nested design was used. Among the surveyed maize fields, 85% of them were infested with the disease. The mean disease incidence in two years ranged from 75% in the eastern Hararghe to 100% in the western Hararghe zone and the severity ranged from 25% to 65%, respectively. Combined analysis over the years also showed that the mean incidence and severity of common rust of maize were significantly associated with the zones (χ2=15, df=1, P=0.0001). The highest mean common rust incidence (95%) and severity (55%) were recorded for Boke, Chiro, Oda Bultum and Tullo districts in the western Hararghe zone whilst Deder, Chelenko, Haramaya and Kombolcha districts of the eastern Hararghe zone had the lowest mean incidence (45%) and severity (25%) scores, respectively. Higher epidemic frequency of the disease was also associated with intermediate and humid areas (Tullo, Boke and Oda Bultum districts) (χ2=30, df=7, P=0.0001). The prevalence, intensity, and importance of the disease was also correlated with cropping systems, altitude, weather variables and varieties used during the survey time (r=0.55; r=0.45; r=0.25 and r=0.50), respectively. It is, thus, concluded, that common rust (Puccinia sorghi Schw.) is the most widely distributed and important foliar disease of maize in Hararghe highlands. Keywords: Ecology; Epidemiology; Eastern Hararghe Zone; Incidence; Prevalence; Severity; Western Hararghe Zone 1. Introduction is not adopted in time, it damages the plant causing Maize (Zea mays L.) is one of the most important cereal higher yield losses (Assefa et al., 1993; Netsanet, 2005; crops in larger parts of the world including Ethiopia Daniel, 2008; Tewabech et al., 2012). (Abate et al., 2015; FAO, 2017). In Ethiopia it is a Common rust causes extensive yellowing and staple food crop and one of the main sources of premature desiccation of maize foliage, resulting in leaf calories in major maize producing regions. It is necrosis, and complete destruction of the cultivated on about 2.135 million hectares of land in photosynthetic areas. In extreme cases, heavy rust the country (CSA, 2018). The national average yield of infestations may result in stunting, incomplete ear tip maize under subsistence production is about 3665 fill and pustules on ear husks, reducing marketability kg/ha (CSA, 2018). This is too much below the world’s and yield. The disease occurs in several maize average yield (Tilahun et al., 2017). This low yield is producing areas in the country, resulting in grain yield attributed to foliar diseases and insect pests such as reductions up to 23% (Fininsa, 2001) and 60.5% yield stalk borers (Dagne et al., 2008; Girma et al., 2015; loss was also noted for susceptible cultivars such as Zelalem et al., 2018). CML- 202 (Deyle et al., 2012). In Ethiopia, the production of maize is threatened by Common rust of maize caused a yield loss of 12-60% a number of biotic and abiotic factors. Among the (Utpal et al., 2012) in Asia and occurs in all maize biotic factors, common rust caused by Puccinia sorghi, is growing areas of the world (Bello et al., 2012; Wang et the most destructive foliar disease of maize in the al., 2014). Similarly, in eastern Ethiopia, Netsanet country. In maize growing regions of Ethiopia, the (2005) reported a disease severity of up to 35% and disease has become a potential threat to maize relative yield loss of 29% in unsprayed plots due to this cultivation (Tewabech et al., 2012). It appears from the pathogen. Currently, common rust has also become the early stages of maize growth and if proper management most important threat to maize production in maize ______________________________________________________________ Licensed under a Creative Commons *Corresponding Author. E-mail: [email protected] Attribution-Non-Commercial 4.0 International License. ©Haramaya University, 2019 ISSN 1993-8195 (Online), ISSN 1992-0407(Print) Bekeko East African Journal of Sciences Volume 13 (2) 134-144 growing areas of Ethiopia causing significant yield some cultural practices. Jeger (2004) and Madden et al. losses (Tewabech et al., 2012). (2007) indicated the importance of the knowledge of In developing countries like Ethiopia, one of the epidemiological features of plant diseases in providing bottlenecks, which are responsible for lowering the useful information for understanding the biology of yielding potential of maize, is the usage of varieties with their causal agents, and its role as the basis for the inferior genes, which are susceptible to diseases, establishment, planning and monitoring of effective insects, weeds, low yielding and inferior quality. In disease management strategies. Understanding disease addition, lack of adequate investment and skilled epidemiology as it is affected by different variables is manpower to improve varieties for high yield and also useful to design ecologically sustainable disease disease resistance as well as, diminishing land and water management tactics and strategies (Madden et al., 2007). resources and environmental stresses are reducing Survey data are useful to gain insight into the yielding potential of the crop (Shiferaw et al., 2014). occurrence, distribution, relative importance of plant In Hararghe highlands of eastern Ethiopia, where diseases and the association of these diseases with maize is grown among the major cereals, in the high cropping systems, environmental factors and cultural rainfall areas such as (Chiro, Doba, Tullo, Mesela, practices (Rusuka et al., 1997). Gemechis, Kuni, Boke, Habro, Darolabu, Deder, However, little documented information is available Chelenko, Haramaya and Kombolcha) foliar diseases to gain insights into occurrence, distribution, and the and soil fertility depletion are major problems relative importance of maize rust in the eastern constraining crop productivity. Intercropping is widely highlands of Ethiopia. used in these areas by combining maize or sorghum This research was, therefore, conducted to determine with the perennial narcotic crop like khat (Catha edulis the prevalence and relative importance of common rust Forsk) and common bean which further exposes the of maize in Hararghe highlands, eastern Ethiopia. soil to rampant nutrient depletion and high disease epidemics leading to poor crop yield (Heluf et al., 1999; 2. Materials and Methods Fininsa, 2001; Ararsa, 2012). In this area, maize is 2.1. Description of the Survey Procedures grown on soils devoid of basic crop nutrients being Field surveys were conducted in different agro- exposed to foliar diseases such as common rust. Hence, ecological zones of eastern Ethiopia (eastern and the genetic potential of hybrids deployed in this region western Hararghe zones) during the 2013 and 2014 will not be fully exploited (Bekeko, 2013; Bekeko, main cropping seasons. The survey route followed 2014). major roads to towns and localities in each zone. A Maize yield is highly variable in rainfed environments total of 230 farmers’ fields in eight districts were of Ethiopia and it is still very low (often less than 4 assessed for the prevalence, intensity and importance of t/ha., CSA, 2018). Therefore, developing and deploying common rust of maize. maize varieties combining high yield potential and Fields were randomly selected at the interval of 5-10 tolerance to major foliar diseases, is vital to reduce the km along the main and accessible rural roads. Within risks associated with planting under rainfed conditions selected fields, three quadrants (4 m * 4 m) diagonally in the highlands of the country (Brummer et al., 2011). spaced about 10 m apart were sampled. All plants in Most of the maize varieties growing in eastern Ethiopia each quadrant were used as sampling units. When are prone to the disease, which inflicts heavy yield necessary, the sample size (the number of observed losses under favorable weather conditions (Bekeko, fields per district) was adjusted to suit the crop 2014; Tilahun et al., 2017; Zelalem et al., 2018). distribution. Similarly, the sample units (the number of Most of the local cultivars, composites and novel quadrants) were adjusted to suit the field size. All of the hybrid maize varieties growing in this area showed sampled fields belonged to smallholder farmers, susceptibility to this disease which can potentially affect research farms and private investors. Each field was the food security of the community. Previous surveys visited once in each of the two years