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Date: Thu 21 May 2009
Source: Ohio Farmer [edited]
<http://ohiofarmer.com/story.aspx?s=23654&c=9>

New mold attacks corn and soybeans

A new species of _Pythium_, a water mold that attacks soybeans and corn in saturated soils, has been identified in Ohio. Anne Dorrance, Ohio State University, says _Pythium delawarii_ was labeled as a new species when its characteristics didn't match any of the more than 200 described _Pythium_ species. There are at least 24 species found in Ohio that affect corn and soybeans.

"_Pythium_ species have different shapes of mycelium and fruiting structures. This new species didn't fit any of the known _Pythium_ descriptions," says Dorrance. "The final evidence was the DNA sequencing, which didn't match any of the described species. It was proof that we indeed did have something that wasn't in any of the data banks."

_Pythium_ pathogens attack via the plant roots. They are one of the major causes of crop replants, and are becoming more economically important because of the continued rise in seed costs. "Producers can't afford to be replanting their crop due to disease issues," says Dorrance.

The new _Pythium_ species was isolated from an Ohio field that experienced persistent stand establishment problems. So far the new species has been identified in a small number of locations across the state and doesn't appear to be very aggressive. "But it is an unusual species in that it thrives in warmer temperatures later in the season on older plants," says Dorrance.

The discovery would aid in future management of _Pythium_ diseases and help in the breeding of new cultivars for resistance and new chemistries for seed treatment compounds. "Right now we are looking at how fungicides affect it and studying the current germplasm for resistance," says Dorrance.

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[_Pythium_ fungi cause damping off, root rots, and blights leading to serious problems in a wide variety of agricultural and horticultural crops.
On maize and soybean seedlings, _Pythium_ species can cause pre- and post-emergence damping off during cold and wet weather in spring. The fungi are soilborne and can also be dispersed by water and mechanical means. Crop rotation is not always effective in controlling _Pythium_ diseases because its effect on pathogen populations can vary. Fungicides, seed treatments, biocontrol agents, and use of resistant crop varieties may also be useful for disease management.

Maps of USA:
<http://www.mapsofworld.com/usa/usa-state-and-capital-map.html>  and <http://healthmap.org/r/00do>
Picture galleries of _Pythium_ symptoms and fungal structures:
<http://www.forestryimages.org/browse/subimages.cfm?SUB=530>  and <http://www.ipmimages.org/browse/subimages.cfm?SUB=530>
Links
_Pythium_ on soybean and maize:
<http://ipm.illinois.edu/bulletin/pastpest/articles/200210c.html>  and <http://journals.cambridge.org/article_S0953756298006510>
Information on _Pythium_ diseases:
<http://www.rbgsyd.nsw.gov.au/science/hot_science_topics/Soilborne_plant_diseases/Vietnam_template3/Pythium>
and
<http://www.reeis.usda.gov/web/crisprojectpages/208746.html>
_P. delawarii_ taxonomy:
<http://www.indexfungorum.org/Names/NamesRecord.asp?RecordID=506729>
Genus _Pythium_ taxonomy:
<http://www.indexfungorum.org/Names/genusrecord.asp?RecordID=20465>
Current _Pythium_ species list via:
<http://www.indexfungorum.org/Names/Names.asp>.  - Mod.DHA]