Distribution of Maize Grey Leaf Spot and Morphological and Cultural Characterization of Cercospora Zeae-Maydis Tehon and Daniels Isolates in Western Oromia Region, Ethiopia

Abstract

Maize (Zea mays) is one of the most widely cultivated crops in the world. It occupies an important position in the world economy serving as food, feed, and industrial grain crop. In Ethiopia, an average productivity is about 3.94 t ha-1 , which is below the world average of 5.78 tones ha-1 . A significant portion of this yield gap is attributable to biotic and abiotic stresses. Diseases play a major role among the biotic constraints. Of these, grey leaf spot (Cercospora zeae-maydis) is one of the major foliar diseases threatening maize production in Ethiopia. Most of the researchers estimated that losses as high as 100% occurred when the pathogen attacked before the flowering stage. Also, in Ethiopia the loss caused due to GLS reached 49.5%. Therefore, the objective of this study was to assess the distribution, of GLS and morphological and cultural characterization, of maize GLS isolates. The field assessment was conducted during 2017 main cropping season by sampling 81 maize fields in 9 districts from 3 zones. Morphological and cultural characterization studies of the 5 isolates were done at JUCAVM Plant Pathology lab and greenhouse, respectively. BH540 moderately susceptible to GLS maize variety was used to confirm the Koch’s postulate of the isolates. The survey result showed the highest disease prevalence 62.96 % was recorded in East Wollega zone and the lowest (22.22%) in West-Wollega zone. The highest mean incidence 35.06 % was recorded in East Wollega zone whilst the lowest 9.51% was found in West-Shewa, The maximum disease Severity index of 31.43% in East Wollega zone followed by West-Shewa having (11.98%) and West-Wollega (10.05%) zones. At a district level, the highest prevalence was recorded in Leka-Dulecha followed by Gobu-Seyo with disease prevalence of 88.9% and 66.7%, respectively, whereas the minimum prevalence was at Ayra-Guliso Gimbi and BakoTibe, each with 22.2 % prevalence. The highest mean disease incidence 48.15% was recorded at Gobu-Seyo district followed by Leka-Dulecha 47.77% whereas the lowest was recorded in Gimbi 1.1% districts. The highest mean disease severity index was recorded in Leka-Dulecha 46.11% followed by Gobu-Seyo 39.15%, whilst the lowest in Gimbi 1.78%. From 155 samples collected during the assessment, 52 isolates were re-cultured and grouped into 5 isolates. Colony color, shape, elevation, edge, conidial shape and number of septa were used to characterize the isolates. Light grey, grey and dark grey were major colony color revealed by the isolates. Based on the Conidial shape, isolates LD-G and DN-H revealed slightly curved whereas isolates GS-O, IG-3, and LA-Ay were straight shape of the conidia. The highest AUDPC and disease severity index were recorded by LD-G and DN-H isolates, with 1540 and 80 %, respectively. The pathogen was re-isolated and Koch’s postulate was proved. From the result, it can be concluded that GLS is prevalent with different intensity and different characteristics across the study areas. Thus, there is a need to develop management strategies like crop rotation with non-host, use of tolerance varieties to reduce the impact of GLS on maize production in the study area