Corn diseases in Algeria: first report of three Bipolaris and two Exserohilum species causing leaf spot and leaf blight diseases

During 2016 and 2017, surveys for leaf diseases were conducted across several corn fields in Algiers (north) and Ghardaia (south) regions, Algeria. Leaves samples exhibiting leaf spots were collected for recovering the potential fungal pathogens associated with the symptoms. Seventy isolates were recovered from the samples and characterized using phylogenetic, morphological, and pathogenic features. The isolates were morphologically grouped into two genera: Exserohilum and Bipolaris. Based on ITS, GAPDH, and RPB2 sequence data, Exserohilum isolates were identified as E. rostratum and E. monoceras, while Bipolaris isolates were identified as B. sorokiniana, B. microlaenae, and B. omanensis. Pathogenicity test was carried out under greenhouse conditions using the susceptible corn cultivars "Giza 352" and "Qing Qing 300." B. sorokiniana caused light green to grayish leaf spots with rounded or irregular margins (0.2-0.5 x 0.2-0.4 mm); some lesions were circular to oval, white-gray with brown margins, surrounded by yellow-green halo (0.3-2.5 x 0.3-1.3 mm). B. microlaenae induced grayish-white or light brown leaf spots, encircled by a reddish border (0.25-0.94 x 0.1-0.52 mm). B. omanensis caused irregular, circular or oval necrotic spots, whitish gray in color and surrounded by a dark brown border (0.4-1.2 x 0.2-0.7 mm). E. rostratum caused grayish brown lesions (0.2-5.0 x 0.2-1.5 mm), which may develop to form tan to dark brown necrotic streaks. Finally, E. monoceras induced grayish or tan lesions (0.2-0.5 x 0.1-0.4 mm), surrounded by yellow or orange halo. The lesions elongated parallel to the veins and may coalesce to form long gray streaks. To our knowledge, this is the first report of these five fungal species associated with corn leaf spots in Algeria. Furthermore, B. microlaenae and B. omanensis are recorded for the first time in the world as causal agents of leaf spot diseases in corn.