Onion leaf blight caused by Alternaria alternata sensu lato and Stemphylium vesicarium in Michoacán, México

Abstract

México is among the main producers of onions, which are cultivated mainly in the states of Baja California, Chihuahua, Guanajuato, Michoacán, and Zacatecas. During June and November 2017, foliar blight symptoms were observed in commercial onion crops in the municipality of Copándaro, Michoacán. The incidence of the disease was 20% in June and 80% in November. The objective of this work was to identify the causal agent or agents of this disease. Fungal isolates recovered from symptomatic plants presented conidia typical of Alternaria and Stemphylium. Molecular identification and phylogenetic analysis using partial sequences of the nuclear ribosomal internal transcribed spacer (ITS) region, the translation elongation factor-1 alpha (TEF1), and RNA polymerase subunit II (RPB2) genes confirmed the identity of the isolates as species within the Alternaria alternata species complex, and Stemphylium vesicarium. The isolates reproduced foliar blight symptoms in inoculated onion plants in pathogenicity tests. This is the first report of Alternaria alternata sensu lato and Stemphylium vesicarium causing foliar blight in commercial onion crops in Michoacán.