Pyricularia oryzae Causing Blast on Foxtail Millet in Iran

Abstract

Each year Pyricularia oryzae causes blast diseases of rice, wheat, and cereals of local importance (millets), which destroy enough food supply to sustain millions of people (Pennisi 2010). Blast disease is one of the major constraints for the production of foxtail millet (Setaria italica), especially in northern China and India (Nakayama et al. 2005). Blast in its severe form causes up to 30 to 40% loss in grain yield in these areas (Nagaraja et al. 2007). In July 2016, during the survey of infected foxtail millet farms in Mazandaran province of Iran, some plants of foxtail millet showing typical blast symptoms were collected. All the leaves and heads of plants in the fields were infected, and disease was widespread on all plants in several fields. Brown spots on heads and lesions on leaves appeared as diamond shape with a light margin. Five isolates of Pyricularia sp. were obtained from disease samples as descripted by Pordel et al. (2015). To determine the species of Pyricularia causing blast on foxtail millet, we sequenced four gene regions (ACT/CAL/ITS/RPB1) used for taxonomic identification of Pyricularia species (Klaubauf et al. 2014). Sequences were generated for two of the five Iranian strains (IR0106 and IR0107) collected on foxtail millet and were aligned with 15 additional sequences of P. oryzae strains from different hosts, and from the closely related species P. pennisetigena, P. penniseticola, P. ctenantheicola, and P. grisea reported in the reference publication of Klaubauf et al. (2014). The two strains were clearly assigned to P. oryzae. Foxtail millet plants were inoculated with the strains isolated from diseased samples following a protocol adapted from Silue et al. (1992). Typical diamond-shaped, dark-bordered lesions with pale centers were visible on leaves of all inoculated plants after 5 days and were similar to lesions observed in the field. Foxtail millet strains caused severe lesions leading to complete leaf wilt. The fungus was reisolated from leaf lesions of inoculated plants and morphologically identified, confirming Koch’s postulates. This disease should be monitored because it may be an emerging problem on foxtail millet crop in Iran, where the area cultivated doubled in 5 years to reach 8,500 ha in 2016 (FAO 2018). This is the first report of blast disease outbreak on foxtail millet in Iran.