First Report of Pythium torulosum Causing Corn Root Rot in Northeastern China

Area of Science:

• Plant Pathology
• Mycology
• Agricultural Science

Background:

• Severe corn (Zea mays) seedling disease, characterized by wilting and root rot, was observed in Heilongjiang province, China.
• Previous research has identified various oomycetes as causal agents of plant root diseases.

Purpose of the Study:

• To identify the pathogen responsible for severe corn root rot in Heilongjiang province.
• To confirm the pathogenicity of the isolated organism and its role in corn root rot.
• To report the first occurrence of Pythium torulosum causing corn root rot in Northeastern China.

Main Methods:

• Soil and symptomatic corn root samples were collected from affected fields.
• Oomycete isolation was performed on selective media (PARP+B), followed by culturing on V8 juice agar.
• Morphological characterization and molecular identification (ITS and CoII gene sequencing) were used to identify the pathogen.
• Pathogenicity was confirmed through inoculation tests on corn seeds, fulfilling Koch's postulates.

Main Results:

• Six oomycete isolates were obtained, with six identified as Pythium torulosum based on morphology.
• Molecular analysis of the internal transcribed spacer (ITS) and cytochrome c oxidase subunit II (CoII) genes confirmed the identification of one isolate ('copt') as P. torulosum.
• Pathogenicity tests demonstrated that P. torulosum isolate 'copt' caused typical root rot symptoms in corn seedlings, and was re-isolated from diseased roots.

Conclusions:

• Pythium torulosum is identified as the causal agent of corn root rot in Heilongjiang province, China.
• This represents the first documented report of P. torulosum causing corn root rot in Northeastern China.
• The presence of this pathogen poses a new threat to corn production in the region, necessitating the development of management strategies.