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European Journal of Applied Sciences – Vol. 10, No. 1

Publication Date: February 25, 2022

DOI:10.14738/aivp.101.11504. Onwunali, M. R. O., & Mabagala, R. B. (2022). First Report of Leaf Blight of Maize (Zea Mays L.) Caused by Exserohilum Rostratum

in Tanzania. European Journal of Applied Sciences, 10(1). 476-481.

Services for Science and Education – United Kingdom

First Report of Leaf Blight of Maize (Zea Mays L.) Caused by

Exserohilum Rostratum in Tanzania

Onwunali, M. R. O.

Department of Agric. Education, Federal College of Education

P.M.B. 1041, Zaria, Nigeria

Mabagala, R. B.

Department of Crop Science and Horticulture

Faculty of Agriculture, Sokoine University of Agriculture

P.O. Box 3005, Morogoro, Tanzania

ABSTRACT

Maize is a popular crop and stable food in the Highlands of Tanzania. In the growing

seasons of 2012 and 2013, leaf blight caused by Exserohilum rostratum was found

for the first time in Ismani village, in Iringa Region. Imani village is located at S07°

27. 463ʹ, E035° 48. 231ʹ, and 1270 to 1284 meter above sea level altitude.

Morphological characteristics of the pathogen showed that the conidia were

cylindrical, rounded at the two ends, brown, smooth with two distinct septation,

with conspicuous protruding hilum at one end of the conidia with average size of

56-128 × 11-18 μm. Conidiophores were solitary, flexuous and geniculate.

Pathogenicity test revealed that inoculum density of 1.0 × 105 conidia/ml showed

apparent symptoms within 48 hrs. of inoculation, and caused widespread necrosis.

Exserohilum rostratum therefore could have potential effect on maize and humans

in Ismani village, and possibly spread to other agro-ecological zones. This is the first

report of the E. rostratum on maize foliage in Tanzania. Therefore, molecular

characterization is needed to variation among Helminthosporum species

pathogens of maize.

Keywords: Exserohilum rostratum, pathogenicity, morphology, virulence, Ismani, Iringa,

Tanzania.

INTRODUCTION

Exserohilum rostratum (Drechs.) Leonard & Suggs., formerly known as Helminthosporum

rostratum (Drechs.) and Drechslera rostrata (Drechs.) is a thermophilic fungus with asexual

reproductive form treated in the genus Exserohilum [1]. Reports also showed that the pathogen

is heterothallic and produced teleomorph in-vitro (ascospores) after pairing different mating

types in culture at low temperature with protuberant conidial hila [2, 3]

Exserohilum rostratum has wide host range and has been reported to cause leaf spots and blight,

crown rot and root rot in maize and grasses [4, 5, 6, 7], sugarcane [8] and banana [9]. The

pathogen inhabits the soils and on textiles particularly in subtropical and tropical regions [10].

However, the disease is pronounced in hot climates regions of Israel, India and Southern USA

and is associated with human diseases such as skin and corneal infection, invasive diseases and

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Onwunali, M. R. O., & Mabagala, R. B. (2022). First Report of Leaf Blight of Maize (Zea Mays L.) Caused by Exserohilum Rostratum in Tanzania.

European Journal of Applied Sciences, 10(1). 476-481.

URL: http://dx.doi.org/10.14738/aivp.101.11504

allergic fungal sinusitis [11]. Exserohilum rostratum prevalence has not been reported on maize

leaf or any other crop in Tanzania. The purpose of this study was to confirm the presence of the

pathogen on maize in Tanzania.

Field surveys were conducted in 480 farmers’ field in Morogoro, Coastal Region, Iringa, Njombe,

Mbeya, Kilimanjaro and Arusha regions in 2012 and 2013 growing seasons primarily for the

devastating northern leaf blight caused by Exserohilum turcicum in maize. Sampling point were

marked (altitude and co-ordinates) with the Global Positioning System (GPS eTrex Legend HCx)

and presumed typical symptoms of turcicum blight were collected for isolation [12, 13, 14, 15,

16, 17, 18]. Of the 480 infected samples, a dematiaceous fungus with morphological variation

in the culture and pathogen structure was consistently isolated from naturally occurring lesions

on maize (Figure 1) from Ismani village in Iringa Region. Such isolates (IIs 3) were obtained

from samples located at S07° 27. 463ʹ, E035° 48. 231ʹ, at altitude of 1270 to 1284 masl. The

isolate was identified as Exserohilum rostratum (Figs. 2) based on cultural and morphological

characteristics (Leonard and Suggs, 1974; Leonard, 1976; Sivanesan, 1987, and virulence.

Figure 1: Typical symptom of maize leaf blight caused by Exserohilum rostratum in the field

ISOLATION OF THE PATHOGEN

Isolation of the pathogen was done under sterile condition using three layers of moist blotter

papers [19] in a 9 cm diameter petri-dish. Plates were incubated for 48 hours at 25oC for 12 h

light and 12 h dark to promote growth and sporulation [20] while single-conidia on V8-juice

agar medium was used to obtain the pure culture and purified by standard hyphal tip isolation

technique [14]. Such cultures were maintained at 24±2°C under fluorescent lighting at 970 lux

for 12 h light and 12 h dark in the Mycology Laboratory, African Seed Health Centre, Sokoine

University of Agriculture, Morogoro, Tanzania.

Temporary slides were made from a 7-day sporulated culture and used to determine conidia

size (length and width) of 50 randomly selected conidia from different field views under 40x

magnifications using ocular ruler in the bifocal Olympus microscope [6]. Conidia were

photographed under such magnification with a Sony Cybershot (10.1 Mega pixels, 5x Optical

Zoom) digital camera.