Pythium spp. associated with stunting and root rot of winter wheat in North Carolina

Authors: REEVES, ELLA - North Carolina State University; KERNS, JAMES - North Carolina State University; Cowger, Christina; SHEW, BARBARA - North Carolina State University

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2020
Publication Date: 3/3/2021
Citation: Reeves, E., Kerns, J., Cowger, C., Shew, B.B. 2021. Pythium spp. associated with stunting and root rot of winter wheat in North Carolina. Plant Disease. 105:986-996. https://doi.org/10.1094/PDIS-09-20-2022-RE.
DOI: https://doi.org/10.1094/PDIS-09-20-2022-RE

Interpretive Summary: In eastern North Carolina, wet winters can lead to mild to severe stunting and root rot of wheat. Three species of a fungus-like soilborne organism (Pythium irregulare, P. vanterpoolii, and P. spinosum) were previously identified as causal agents of Pythium root rot of wheat in this region. To see which species were associated with wheat root damage, 114 isolates of Pythium were derived from wheat plants that were collected in 8 counties and showed symptoms of stunting. Twelve Pythium species were recovered, and P. irregulare (32%), P. vanterpoolii (17%), and P. spinosum (16%) were the most common. Testing isolates of these Pythium species on wheat seedlings in growth chambers, we observed slight to severe necrosis (browning, rotting) of young roots. The disease-causing ability of five isolates each of P. irregulare, P. vanterpoolii, and P. spinosum was compared on a single variety of wheat at 14°C, and highly aggressive isolates were found within all species. Growth of these isolates was measured at 14°C and 20°C on Petri plates, and all isolates grew faster at the higher temperature. The fastest growing isolates at 14°C were among the most aggressive. The effects of varying nitrogen levels and temperatures on root rot caused by Pythium species alone or in combination were investigated. All inoculation treatments caused severe root rot under all conditions tested, and disease was more severe at 12/14°C compared to 18/20°C, but there was no effect of nitrogen application.

Technical Abstract: In eastern North Carolina, mild to severe stunting and root rot have reduced yields of winter wheat, especially during years with abundant rainfall. Pythium irregulare, P. vanterpoolii, and P. spinosum were previously identified as causal agents of Pythium root rot of wheat in this region. To investigate species prevalence, 114 isolates of Pythium were derived from symptomatic wheat plants collected in 8 counties. Twelve species were recovered, and P. irregulare (32%), P. vanterpoolii (17%), and P. spinosum (16%) were the most common. Pathogenicity screens were performed with selected isolates, and slight to severe necrosis of young roots was observed. The aggressiveness of five isolates each of P. irregulare, P. vanterpoolii, and P. spinosum was compared on a single cultivar of wheat at 14°C, and highly aggressive isolates were found within all species. In vitro growth of these isolates was measured at 14°C and 20°C, and all isolates grew faster at the higher temperature. The fastest growing isolates at 14°C were among the most aggressive. The effects of varying nitrogen levels and temperature on root rot caused by Pythium species alone or in combination were investigated. All inoculation treatments caused severe root rot under all conditions tested, and disease was more severe at 12/14°C compared to 18/20°C, but there was no effect of nitrogen application.