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
