These are oospores of the plant pathogenic oomycete (water mold) Phytophthoria sojae. This fungus-like microbe causes a serious root and stem rot disease of soybeans. The oospores are very effective survival structures and they can remain dormant in the soil for several years.
Oomycetes are actually in a kingdom distinct from fungi, plants and animals. Phytophthora species are pathogens of a wide diversity of plants, including trees and shrubs of native ecosystems as well as agricultural crops. They cause damage costing tens of billions of dollars per year. The particularly virulent P. ramorum is currently a major pathogen of coastal oak trees in California, causing Sudden Oak Death on both oaks and shrubs in oak forests.
P. sojae is being used as a model species for the genus. Its genome is being sequenced and a wide range of genetic and genomic resources (including genetic maps, BAC libraries, and EST sequence) have been developed and are being used to better understand all species of Phytophthora.
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