Three pythium species isolated from severely stunted wheat during an outbreak in North Carolina

Abstract

Large portions of eastern North Carolina experienced prolonged soil waterlogging in 2016. Severely stunted wheat plants from saturated fields were examined and Pythiumspp. consistently were associated with the symptoms observed. Three species of Pythium were identified among 15 isolates derived from wheat roots and crowns: P. irregulare, P. spinosum, and P. vanterpoolii. Each species was isolated from samples that came from between two and five counties. Pythium vanterpoolii and P. spinosum have not previously been reported as pathogens inwheat in the United States. All three species caused root rot when reinoculated on wheat plants. These species are not opportunistic or mainly saprophytic on other hosts; therefore, it is likely that they contributed to the extreme stunting and yield loss observed in North Carolina wheat in 2016. The 15 isolates were tested for sensitivity to mefenoxam at 100 μg/ml a.i. and none was insensitive. Prolonged hypoxia likely predisposed North Carolina wheat to unusual levels of Pythiumroot rot in 2016.