Why and how do some plant pathogens jump to new hosts?

Some plant pathogens stay with one host lineage for a very long time, while others jump to new species, sometimes with devastating results for crops. Understanding what makes a jump possible could help predict, and perhaps prevent, the next epidemic.

Question

Why, and by what mechanisms, are some plant pathogens able to extend their host range by jumping to new host species? The question covers fungi, oomycetes, bacteria and viruses, from the molecular level (pathogen effectors and host resistance genes) to ecology (contact between hosts through farming and trade), on evolutionary and present-day timescales.

Background

The question belongs to the category "Plant–Environment Interactions" of the 2023 list of 100 important questions facing plant science, next to a related question on how broad-host-range pathogens stay virulent on many hosts [1]. Host jumps are a source of emerging crop diseases, and global trade and changing climates keep bringing pathogens into contact with new potential hosts.

What is known

• A review concluded that host jumps are common even in obligate biotrophic pathogens, are facilitated by effector innovations, stress, compatible pathogens and physiological similarity between hosts, and that jumping, establishment and speciation can happen within centuries to millennia [2].
• Inoculation experiments in a tropical forest showed that most fungal leaf pathogens can infect several hosts, but the likelihood that a pathogen infects two plant species declines steadily with their phylogenetic distance, which makes host ranges partly predictable [3].
• Wheat blast emerged in Brazil in the 1980s. Genetic analysis showed that wheat varieties with a disabled resistance gene were susceptible to strains that infected oat and ryegrass, and that later changes in the pathogen increased its virulence on wheat [4].
• When wheat blast appeared in Bangladesh in 2016, affecting about 15,000 hectares with yield losses up to 100%, genomic surveillance traced it within weeks to a South American wheat-infecting lineage of Magnaporthe oryzae [5].

What would count as progress

No single result settles a question like this; contributions like these would move it forward:

• Host-range datasets from systematic cross-inoculation experiments, combined with host phylogenies and pathogen genomes and released openly, to test what predicts a jump.
• Comparative genomics of related pathogen lineages on different hosts that identifies the effector or resistance-gene changes enabling a jump, confirmed by functional tests.
• A risk model that ranks pathogen–crop pairs by the likelihood of a jump, evaluated against newly recorded host associations.

References

1. Armstrong, E. M. et al. (2023). One hundred important questions facing plant science: an international perspective. New Phytologist 238(2), 470–481.
2. Thines, M. (2019). An evolutionary framework for host shifts – jumping ships for survival. New Phytologist 224(2), 605–617.
3. Gilbert, G. S. & Webb, C. O. (2007). Phylogenetic signal in plant pathogen–host range. Proceedings of the National Academy of Sciences 104(12), 4979–4983.
4. Inoue, Y. et al. (2017). Evolution of the wheat blast fungus through functional losses in a host specificity determinant. Science 357(6346), 80–83.
5. Islam, M. T. et al. (2016). Emergence of wheat blast in Bangladesh was caused by a South American lineage of Magnaporthe oryzae. BMC Biology 14, 84.

Source

Imported from One hundred important questions facing plant science, question 80, curated by Armstrong et al. Listed as open in the source (2023) and still an active research question as of 2026-10-20. The statement above is written in our own words; see the source for the original wording, history and discussion.