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Abstract

Cereal blast is one of the most threatening plant diseases worldwide and impacts the most common cereal crops, including rice, wheat, and barley. Despite a prevalent lack of sexual recombination in most natural populations, the blast fungus continuously adapts to its host plants which can lead to host-jumps and recurrent pandemics. A major driver of host-adaptation is rapid genomic changes that lead to a gain and loss of effector genes. However, the molecular details that enable rapid genomic changes are not well understood. We established a state-of-the art, multidisciplinary approach to analyse structural variations including mini-chromosomes and identify mini-chromosome associated genes that likely contribute to virulence of the blast fungus. Mini-chromosomes in wheat- and rice-infect- ing blast fungus isolates contribute to their genomic diversity by horizontal mini-chromosome transfer and inter-chromosomal recom- bination with core-chromosomes leading to lineage- or isolate-specific genome arrangements that involve effector candidates. These structural changes in the genome facilitate gene gains or losses of virulence factors and ultimately enable rapid adaptation to varying host conditions. Using this approach, we identified several effector candidates that differentiate two sub-lineages of a pandemic wheat blast lineage. Our results suggest that mini-chromosomes are major drivers of genetic diversity and host adaptation in the blast fungus. We will leverage this knowledge to identify novel virulence genes and potential sources of resistance against the blast disease.