New research with Imperial College London and CABI has revealed that the fungus that causes coffee wilt disease repeatedly took up segments of DNA from a related fungal pathogen, contributing to successive outbreaks of the disease.
During the past century, outbreaks caused by the fungal pathogen Fusarium xylarioides have severely impacted coffee production across sub-Saharan Africa. Despite being discovered in 1927, little is known about the pathogen’s genetics and evolution, and this understanding is crucial for managing future outbreaks.
Researchers compared the genomes of 13 historic strains spanning six decades, including those from CABI’s Culture Collection, and multiple disease outbreaks to investigate how the pathogen has evolved and adapted to its host plants. They found that F. xylarioides is made up of at least four distinct lineages: one specialised to live on arabica coffee plants, one adapted to robusta coffee plants, and two historic lineages that lived on related coffee species. The researchers also found evidence that these strains had repeatedly received segments of DNA from another fungal pathogen, F. oxysporum, which enhanced F. xylarioides’s infection ability. These additions of DNA, called horizontal gene transfer, likely contributed to the repeated emergence of coffee wilt disease on the African continent.
Coffee is a primary source of income for more than 12 million households in Africa and contributes a significant proportion of tax income in a number of these countries. Ethiopia, for example, records an export value of $762.8m annually.
Lily Peck (Imperial College London) said: “To improve the disease management of fungal pathogens such as Fusarium xylarioides, it is crucial to understand their genetic structure and evolutionary potential. The presence/absence of large genomic regions across populations showed that horizontal transfers of effector genes from members of the F. xylarioides species complex contributed to host specificity.”
Professor Timothy Barraclough said:
“Widespread sharing of specific transposons* between F. xylarioides and F. oxysporum, and the correspondence of putative horizontally transferred regions to a Starship (large mobile element involved in horizontal gene transfers in fungi), reinforce the inference of horizontal transfers and suggest that mobile elements were involved.”
Dr Matthew Ryan (CABI) said: “The fact that horizontal gene transfers between two different species of Fusarium contributed to the repeated emergence of coffee wilt disease is a key mechanism to understand what is happening more widely in fungi – to what extent, we just do not know. There are also sanitary phytosanitary implications in the coffee value chain particularly when it comes to the potentially lucrative export of various coffee varieties to national and international export markets.”
*Transposons, also known as “jumping genes,” are DNA sequences that can move around in the genome of a cell. They are found in many organisms, including bacteria, yeasts, humans, mice, fruit flies and frogs.
To read more about this research, published in PLOS Biology, visit: doi.org/10.1371/journal.pbio.3002480
