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Rust epidemics: Are the alternate hosts the culprit?

Anna Berlin: Swedish Univ of Agricultural Sciences

<div>Most plants can be infected by rust fungi. The rust fungi may have up to five spore stages and many have two hosts, often one perennial and one annual plant species. The sexual cycle is completed on the aecial hosts, which creates new variants of the fungi through genetic recombination. In addition, each aecium or aecial cup may be a unique individual and only share half of its genetic material with its sibling in the neighboring cup. This creates a large amount of genetic diversity from each successful completion of the rust fungal life cycle. Concurrently, the asexual, clonal propagation on the telial host will enable successful fungal individuals to produce enormous amounts of spores of the same genotype. To investigate the role of the alternate host, the population biology of different types of rust species have been studied. If a rust fungal population completes its sexual stage within the region, compared to if it survives in its clonal, uredinial stage, it will have a profound effect on the epidemiology of the disease. A question is what the advantage is for rust fungi to have two hosts. By using two seasons samples from a spore trapping network, and molecular detection of rust fungi through sequencing, a factor describing the quantity of different spores stages could be inferred by calculating the relative abundance of the number of sequence reads, in connection with data on the phenology of the hosts. To understand the contribution of each spore stage in an epidemic, these factors were included in a model to describe different epidemiological scenarios.</div>

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