The Key to Pythium species
The key is presented as a guide to identifying Pythium to the species level. It is a modification of that created by Anna van der Plaats-Niterink (Van der Plaats-Niterink, A. J. 1981. Monograph of the genus Pythium. Studies in Mycology. Baarn, Centraalbureau voor Schimmelcultures. Monograph No. 21:242). Some but not all species of Pythium are included. This key is only a guide and diagnostic tool to assist in the identification of Pythium species. To learn more about identifying Pythium species, culturing Pythium, and Pythium in general visit https://plantpath.psu.edu/Pythium and work through the Module set.
Be flexible in your interpretation of what you observe and observe cultures over time. As you gain experience through looking at many different Pythium cultures, you will begin to be able to differentiate sporangia from oogonia, slightly inflated filamentous sporangia from hyphae, and recognize proliferating sporangia. At first, just reading descriptions is confusing, but the more cultures you observe the process will become much easier.
The key was built using the Lucid Builder program. When you open the key, the window is divided into four sections: features available, features chosen, entities remaining and entities discarded. The culture characteristics are present in the Lucid key as “features”. Pythium species are present as “entities”.
As you look at Pythium cultures, check off the characters you observe on the character checklist. Check off characters by expanding the options beneath each main heading of the “features available” section and click on the empty box next to the character you have observed in your culture. When a character is selected, a check mark will be placed next to that character in the “features available” section. These selected characters will also be copied into the “features chosen” section. In order remove a feature chosen, simply click the checked box next to the unwanted character, and it will become unchecked again. Lastly, as you select the characters you are observing, Pythium species are discarded into the “entities discarded” section, leaving fewer and fewer “entities remaining,” or possible Pythium species.
To help you identify Pythium species, images of the characters are available in the Lucid key. To view these images, make sure that “image thumbnails” is selected under the view tab. Simply expand the contents of the “features available” section and click on the thumbnails to enlarge the images.
Be flexible in using the key. If you are not certain of a characteristic, select one option for that characteristic and see where the key takes you. When you have eliminated most species, examine the description of the species to which you are led and see if it fits. If the descriptions do not match what you have observed, go back and select a different option for that characteristic and other questionable characters and examine the description of the species to which you come.
Authors:
Gary W. Moorman, Ph.D.
Department of Plant Pathology and Environmental Microbiology
The Pennsylvania State University
111 Buckhout Laboratory
University Park, PA 16802
Phone: 814-863-7401
Email: [email protected]
Sara May
Department of Plant Pathology and Environmental Microbiology
The Pennsylvania State University
220 Buckhout Laboratory
University Park, PA 16802
Phone: 814-865-2204
Email: [email protected]
Kathleen M. Ayers
Department of Plant Pathology and Environmental Microbiology
The Pennsylvania State University
220 Buckhout Laboratory
University Park, PA 16802
Email: [email protected]
Key Author(s): Gary W. Moorman, Ph.D., Sara May, Kathleen M. Ayers Key Version: 1.0
