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Cryptosexuality and the Genetic Diversity Paradox in Coffee Rust, Hemileia vastatrix

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Health & Diseases
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Biological & environmental
Carlos Roberto Carvalho, Ronaldo C. Fernandes, Guilherme Mendes Almeida Carvalho, Robert W. Barreto, Harry C. Evans

Despite the fact that coffee rust was first investigated scientifically more than a century ago, and that the disease is one of the major constraints to coffee production – constantly changing the socio-economic and historical landscape of the crop – critical aspects of the life cycle of the pathogen, Hemileia vastatrix, remain unclear. The asexual urediniospores are regarded as the only functional propagule: theoretically, making H. vastatrix a clonal species. However, the well-documented emergence of new rust pathotypes and the breakdown in genetic resistance of coffee cultivars, present a paradox.

Here, using computer-assisted DNA image cytometry, following a modified nuclear stoichiometric staining technique with Feulgen, we show that meiosis occurs within the urediniospores. Stages of spore development were categorised based on morphology, from the spore-mother cell through to the germinating spore, and the relative nuclear DNA content was quantified statistically at each stage.