Soybean Rust
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Phakopsora pachyrhizi is considered the Australasian species of soybean rust and P. meibomiae is a new world species. P. pachyrhizi is the species currently causing damage in the Southern Hemisphere. Both have the same types of lesions and urediniospore morphology and thus cannot be distinguished except using molecular techniques.
Soybean rust forms two types of lesions on leaves, tan and reddish brown. The tan lesions (Figures 5 and 6) when mature, consist of small pustules with masses of tan colored urediniospores on the surface.
Figure 5. Tan lesion of soybean rust
Figure 6. Close up of tan lesions of soybean on a soybean leaf.
Courtesy of Reid Frederrick, USDA, ARS, Ft. Detrick, MDand Arnold Tschanz, USDA, APHIS, PPQ, Riverdale, MD.
Reddish brown lesions (Figures 7and 8) appear different with reddish brown necrotic areas surrounding the pustules.
Figure 7. Soybean rust tan lesions
Figure 8. Close-up of reddish-brown lesion.
Reddish-brown lesions in the center.
Courtesy of Joe Hennen, Botanical Research Institute, Ft. Worth, TX and Arnold Tschanz, USDA, APHIS, PPQ, Riverdale, MD
