Quick Guide for Uromyces vs. Phakopsora - Plant and Pest Diagnostic Laboratory, Purdue University

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Quick Guide for Uromyces vs. Phakopsora

Compiled by Ian Thompson, Purdue University

Phakopsora pachyrhizi may infect several legume hosts in the Midwest and its host range overlaps with other rust species. The overlapping host range raises the possibility of misidentification. This table resents information and images that can be used to differentiate P. pachyrhizi from other rust species that occur on leguminous hosts in the region. Unless otherwise noted below, all pictures are courtesy of Ian Thompson, Purdue University.

Click on image to enlarge

	Uromyces sp.^1,2	P. pachyrhizi¹
Hosts	Uromyces spp. and P. pachyrhizi share many of the same hosts including Phaseolus spp. (beans), Pisum sp. (Pea), Trifolium spp. (clover), Vicia spp (Vetch)., Desmodium spp. (tick trefoil), Lespedeza spp. (lespedeza)
Sori	Cinnamon or rust colored, darker brown or black late in season. Spores erumpent and emerging through the epidermis. May be present on both surfaces of leaves (amphigenous sori)	Brown. Spores emerging through a small pore or covered by epidermis. Present only on underside of leaves. Image by R. Balardin
Paraphyses	Most Uromyces spp. lack paraphyses. When paraphyses are present they will lack distinctly thickened apex.	Paraphyses present at the margin of sori. Paraphyses are 5-13 mm wide and distinctly thickened at the apex . Image by USDA-SBML
Urediniospores	Generally obovoid or ellipsoid, pigmented, golden to cinnamon brown. Walls generally thicker (1.5 – 2.5 µm) than P. pachyrhizi.	More pear-shaped, lightly pigmented or lacking pigment. Walls generally thinner (1-1.5 µm) than Uromyces. Image by USDA-SBML
Teliospores	Generally present, especially later in season. Emerging through epidermis. Obovoid, ellipsoid, or globose. Pigmented, golden to chestnut brown. Pedicles often present. Apical germpore often covered by distinct umbo.	Not produced during growing season.

¹ Uromyces spp. can generally differentiated from Phakopsorapachyrhizi by the presence of thick walled, darker pigmented urediniospores. Some Phakopsorapachyrhizi urediniospores may be distinctly pear-shaped, whereas Uromyces spp do not produce pear-shaped urediniospores. Phakopsorapachyrhizi may not produce telia during our growing season, but Uromyces spp. often do (though they may not always be present).

² Morphological descriptions generalized from Cummins, G.B. 1978. Rust Fungi on Legumes and Composites in North America. University of Arizona Press, Tucson AZ.