Farmers and governments alike fear the emergence of new pest species, as they are more likely to develop pesticide resistance and have devastating consequences. However, nobody has been able to pin-point specific mechanisms leading to the formation of new pest species, until now.

A team of researchers from the Max Planck Institute in Marburg along with colleagues from Aarhus University in Demark have found not only how a new pest species arose, but also how quickly this event occurred. The study was published online July 3rd, in Proceedings of the National Academy of Sciences.

Researchers compared the genomes of a fungus causing "speckled wheat blotch" in Europe, and a related species that damages wild grasses in Iran. Genomic analysis showed that the fungus species that now plagues Middle Eastern plants, Zymoseptoria tritici, and the European pest, Zymoseptoria pseudotritici, branched off to become separate species only 200 years ago. In addition, these two new hybrid species arose solely from two parent species.

The creation of new hybrid species is not new. For example, wild sunflowers originated from a cross between two sunflower relatives, which resulted in a hybrid plant carrying a genome different enough that allowed the plant to adapt to new environments. However, these speciation events can take millennia, at least, and the genome of these news species rarely contain the same exact genes from the original parent organisms.

In this new study, because the speciation event was so recent, researchers were able to analyze the genomes of both parent and hybrid offspring and determine the evolutionary history of the new species. Their results pinpoint to the genomic adaptations that allowed Zymoseptoria tritici to infect wild grasses in Iran, and Z. pseudotitici to damage a wide range of wheat products in Europe and North America.

This study has important implications for the world trade of agricultural products (and their pests).

"World trade promotes the rapid evolution of plant pests. This happens very simply by local fungal species, unintentionally brought into contact with introduced species, which can then cross and form new species," said Dr. Eva Stuckenbrock, from the Max Planck Institute, who led the study.

Original Article:
"Fusion of two divergent fungal individuals led to the recent emergence of a unique widespread pathogen species" (DOI: 10.1073/pnas.1201403109)