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The fusarium wilt fungus was born in California; it goes after vulnerable palms.

The scientists confirm the presence of genetically differentiated lineages with different host-specificity for arabica and robusta coffee and show that the fungal pathogen F. xylarioides repeatedly took up "horizontally transferred" segments of DNA from a related fungal Fusarium taxa which contributed to successive outbreaks of the disease.

Dr Peck also said that multiple transfers into F. xylarioides populations matched different parts of the Fusarium oxysporum mobile pathogenicity chromosome and were enriched in effector genes and transposons.

"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," he said.

They add that knowledge of horizontal transfer mechanisms and putative donor taxa might help to design future intercropping strategies that minimize the risk of transfer of effector genes between closely related Fusarium taxa.