Pyricularia graminis-tritici, a new Pyricularia species causing wheat blast

Area of Science:

• Plant Pathology
• Mycology
• Evolutionary Biology

Background:

• Pyricularia oryzae causes blast disease on numerous grass species globally.
• P. oryzae is a major rice pathogen and an emerging wheat pathogen in Brazil.
• Blast disease impacts wheat and other Poaceae crops, necessitating understanding of pathogen diversity.

Purpose of the Study:

• To investigate the genetic diversity and phylogenetic relationships of Pyricularia isolates from wheat, rice, and grasses in Brazil.
• To identify distinct Pyricularia species causing blast disease in sympatric Poaceae populations.
• To determine the pathogenicity spectrum of identified Pyricularia species on various hosts.

Main Methods:

• Phylogenetic analyses using 10 housekeeping loci from 128 Pyricularia isolates.
• Sampling isolates from sympatric populations of wheat, rice, and grasses.
• Pathogenicity assays on key crop species like wheat, barley, oats, and signal grass.

Main Results:

• Phylogenetic analysis revealed three distinct clades of Pyricularia.
• Clade 1 represents the rice pathogen (P. oryzae pathotype Oryza, PoO).
• Clade 2 represents the wheat pathogen (P. oryzae pathotype Triticum, PoT).
• Clade 3, distinct from P. oryzae, identified as a new species, Pyricularia graminis-tritici (Pgt).
• Pgt and PoT showed high aggressiveness on wheat, barley, oats, and signal grass.
• PoO was virulent on rice, wheat, barley, and oats, but not signal grass.

Conclusions:

• Blast disease in Brazil is caused by multiple Pyricularia species, including the newly described P. graminis-tritici.
• P. graminis-tritici poses a significant threat to global wheat cultivation, as evidenced by its presence in Bangladesh.
• Understanding Pyricularia species diversity is crucial for managing blast disease in agricultural systems.