Weed hosts of the sugarcane root rot pathogen, Pythium arrhenomanes

Weeds in the Poaceae and Cyperaceae families prevalent in sugarcane fields were evaluated as potential hosts for the root rot pathogen, Pythium arrhenomanes. In greenhouse studies, bermudagrass, broadleaf signalgrass, browntop panicum, barnyardgrass, large crabgrass, goosegrass, itchgrass, johnsongrass, Italian ryegrass, and purple nutsedge became infected when grown in steam-treated soil infested with P. arrhenomanes. However, the extent of root colonization, symptom severity, and growth reductions varied among species. Symptom severity and root colonization by P. arrhenomanes were less when weeds were grown in sugarcane field soil in the greenhouse than when weeds were grown in Pythium-infested, steam-treated field soil. Levels of root colonization by P. arrhenomanes in both experiments were greatest for johnsongrass and itchgrass and lowest for browntop panicum, goosegrass, and Italian ryegrass. For weeds collected from sugarcane fields, frequencies for colonized plants were moderate to high, but the extent of root colonization by P. arrhenomanes was low for all except johnsongrass. The results indicate that weeds can serve as hosts for P. arrhenomanes and may play roles in the epidemiology of Pythium root rot on sugarcane.