Diagnostic
Characters for Soybean Rust Identification
Phakopsora
characteristics
Phakopsora pachyrhizi
and Phakopsora meibomiae produce two types of spores. Uredinia
and urediniospores (Figures 15 and 16) are produced throughout
the growing season and teliospores are rarely seen. Observation
of these spores confirms the presence of soybean rust, but it
is not possible to to distinguish the two species based on urediniospore
morphology.
Click on the small image for a larger image.
Figure 15. Cross section of Phakopsora pachyrhizi uredinia on soybean leaf. AVRDC,
courtesy of Arnold Tschanz, USDA, APHIS, PPQ, Riverdale, MD
Figure 16. Phakopsora pachyrhizi urediniospores and
paraphyses which appear identical to those of P. meibomiae. Mary
Palm, USDA, APHIS, PPQ, Beltsville, MD
The only
stage soybean rust that can be used to distinguish Phakopsora
pachyrhizi from P. meibomiae are the telia which rarely
occur in nature. Figures 17 and 18 show the characteristics of P. pachyrhizi on soybean leaf.
Figure 17. Telia of soybean rust on soybean leaf surface. AVRDC,
courtesy of Arnold Tschanz, USDA, APHIS, PPQ
Figure 18. Phakopsora pachyrhizi teliospores in within
telia in a soybean leaf. AVRDC,
courtesy of Arnold Tschanz, USDA, APHIS, PPQ
The two species
must be distinguished using molecular techniques. See the
Identification Verification page.
For a description
of the two species with photomicrographs and the results of recent
molecular taxonomy investigations, see the following references:
Ono, Y, P
Buritica, and JF Hennen (1992) Mycological Research. 96:825-850
Frederick, RD, CL Snyder, GL Peterson, MR Bonde (2002) Phytopathology 92:217-227
