Confirmation of the identity of Exserohilum turcicum, causal agent of maize leaf blight in Sinaloa

Abstract

Fungal diseases constitute an important maize production constraint in Sinaloa, Mexico. In recent growing seasons, a severe foliar epiphytotic disease has occurred in the northern coastal region of this state. The symptoms of the disease resembled those caused by Exserohilum turcicum, reported in the high humid valleys in the states of the central plateau of Mexico and other parts of the world with temperate to subtropical climate. The objective of this research was to confirm the identity of E. turcicum associated to maize leaf blight and to assess the disease severity in 17 maize hybrids in commercial fields. Variation in color and colony morphology of the fungal isolates was observed in various media. The maize leaf extract agar was the most favorable medium for fast mycelial growth of the fungal isolates. The isolates collected were used in pathogenicity tests, where they exhibited a variation in pathogenicity on the commercial maize hybrid DK-3000. Koch´s postulates were fulfilled by re-isolation of the pathogen from inoculated plants. Although the teleomorph (Setosphaeria turcica) was not observed, morphometric and molecular studies indicated that E. turcicum is the causal agent of maize leaf blight. Differential disease severity occurred in maize hybrids and was highly dependent on prolonged periods of high relative humidity. Future research should focus on determining the formae specialis crucial for maize breeding programs to achieve genetic resistance against the disease.