4.5 Article

Tracing the Origin and Evolutionary History of Pyricularia oryzae Infecting Maize and Barnyard Grass

Journal

PHYTOPATHOLOGY
Volume 111, Issue 1, Pages 128-136

Publisher

AMER PHYTOPATHOLOGICAL SOC
DOI: 10.1094/PHYTO-09-20-0423-R

Keywords

blast; emergence; evolution; genomics; host range; Magnaporthe oryzae; maize; new disease; pathogen detection

Categories

Funding

  1. High Council for Research of the University of Tehran
  2. LabEx CeMEB, an ANR Investissements d'avenir program [ANR-10-LABX-04-01]
  3. ANR grant MagMAX [ANR-18-CE20-0016]
  4. CIRAD Institute
  5. Agence Nationale de la Recherche (ANR) [ANR-18-CE20-0016] Funding Source: Agence Nationale de la Recherche (ANR)

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Blast disease is a notorious fungal disease causing dramatic yield losses on major food crops like rice and wheat. The emergence of blast disease on maize in Iran, as well as epidemics on barnyard grass, raises concerns about potential yield losses and geographic expansion of the disease. Phylogenetic analyses indicate independent host-range expansion events from barnyard grass to maize.
Blast disease is a notorious fungal disease leading to dramatic yield losses on major food crops such as rice and wheat. The causal agent, Pyricularia oryzae, encompasses different lineages, each having a different host range. Host shifts are suspected to have occurred in this species from Setaria spp. to rice and from Lolium spp. to wheat. The emergence of blast disease on maize in Iran was observed for the first time in the north of the country in 2012. We later identified blast disease in two additional regions of Iran: Gilan in 2013 and Golestan in 2016. Epidemics on the weed barnyard grass (Echinochloa spp.) were also observed in the same maize fields. Here, we showed that P. oryzae is the causal agent of this disease on both hosts. Pathogenicity assays in the greenhouse revealed that strains from maize can infect barnyard grass and conversely. However, genotyping with simple sequence repeat markers and comparative genomics showed that strains causing field epidemics on maize and on barnyard grass are different, although they belong to the same previously undescribed Glade of P. oryzae. Phylogenetic analyses including these strains and a maize strain collected in Gabon in 1985 revealed two independent host-range expansion events from barnyard grass to maize. Comparative genomics between maize and barnyard grass strains revealed the presence or absence of five candidate genes associated with host specificity on maize, with the deletion of a small genomic region possibly responsible for adaptation to maize. This recent emergence of P. oryzae on maize provides a case study to understand host range expansion. Epidemics on maize raise concerns about potential yield losses on this crop in Iran and potential geographic expansion of the disease.

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