The single and combined effects of nematodes and the sugarcane root-rot pathogen, Pythium arrhenomanes, were evaluated in greenhouse trials conducted in 1996, 1997, and 1998. Individually, P. arrhenomanes and nematodes both reduced shoot and root growth. A community comprised of Mesocriconema xenoplax, Paratrichodorus minor and Tylenchorhynchus annulatus consistently reduced root growth across two infestation levels. Shoot growth was suppressed only at the highest infestation level. Shoot and root growth were consistently suppressed by both low and high infestation levels of P. arrhenomanes. Significant interactions occurred between nematodes and P. arrhenomanes. The fungus reduced nematode populations resulting in a less than additive response for plant growth suppression. Root colonization by P. arrhenomanes was influenced by nematode infestation in only one year. Temperature had an impact on the pathogens. Reproduction by T. annulatus was higher at 30°C than 20°C. The inverse of was observed for reproduction of M. xenoplax, P. minor and root colonization by P. arrhenomanes. The relative importance and interactions among these soil borne pathogens affecting sugarcane will depend on weather and soil conditions.
