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United States Department of Agriculture

Agricultural Research Service

Research on rust fungi
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Phakopsora meibomiaeRust fungi (Basidiomycota, Uredinales) are the largest group of fungal plant pathogens, containing  > 7000 species that possess the most complex life cycles in the Kingdom Fungi. Phylogenetic inference within the Uredinales has been limited by a lack of morphological characters and incomplete life cycle and host-specificity data and the inability to grow these organisms in pure culture.  Although molecular characters have greatly improved resolution of phylogenetic relationships for other major groups of fungi, their use in rust systematics has been extremely limited.  In this research, several genes across a broad swath of Uredinales are being used to resolve systematic conflicts and provide a backbone for future phylogenetic endeavors and are also providing the basis for rapid molecular-based diagnoses of new, important, or invasive rusts.

Objectives of this research are:

  • Develop a global phylogeny for Uredinales and apply this framework as a model for evaluating hypotheses about the evolution of pathogens, pathogenicity, and host selection and for making rapid molecular-based identifications of important rusts.
  • Develop Uromyces appendiculatus as a model organism for studying questions regarding co-evolution, virulence, and population biology.

Uropyxis diphysaeAs a result of this research rust-specific molecular protocols have been developed, numerous gene loci have been tested for their applicability at different levels of phylogenetic inquiry, and rust-specific primers have been designed for loci of interest. This work provides the first set of broad-range rust-specific molecular tools, paving the way for systematic studies of these previously recalcitrant organisms.  Results are being used to identify rusts from around the world implicated in agricultural disease epidemics, and also as potential biocontrol of invasive weeds.

Two major gene pools of the dry bean rust, Uromyces appendiculatus, have been identified that correspond to the gene pools of their host, Phaseolus vulgaris.  A rapid diagnostic test was developed for quickly genotyping isolates of U. appendiculatus, and results from this research have been incorporated into bean breeding programs.

Last Modified: 8/13/2016
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