First Report of Pythium aphanidermatum on Basella rubra in Japan

Area of Science:

• Plant Pathology
• Mycology
• Agricultural Science

Background:

• Basella rubra L. (Indian spinach) is cultivated globally for ornamental and culinary purposes.
• A severe rot disease affecting leaves, stems, and roots was observed in cv. Midori in Tokushima Prefecture, Japan.
• The disease caused significant damage, with over 50% of approximately 2,100 plants destroyed.

Purpose of the Study:

• To identify the causal agent of the observed rot disease in Basella rubra.
• To characterize the isolated pathogen morphologically and physiologically.
• To confirm the pathogenicity of the isolated organism on Basella rubra.

Main Methods:

• Isolation and identification of the pathogen from infected B. rubra tissues.
• Morphological characterization using grass leaf water culture and measurement of key structures (hyphae, oogonia, antheridia, oospores).
• Determination of cardinal growth temperatures and pathogenicity tests on wounded B. rubra plants under controlled conditions.

Main Results:

• A Pythium species was consistently isolated and identified as Pythium aphanidermatum (isolate OPU743).
• Morphological characteristics and growth parameters (min/opt/max temps, radial growth rate) were documented.
• Pathogenicity tests confirmed that P. aphanidermatum caused dark brown rot in 66.7% of inoculated B. rubra plants within two days.

Conclusions:

• Pythium aphanidermatum is identified as the causal agent of a severe rot disease in Basella rubra in Japan.
• This represents the first report of P. aphanidermatum causing disease on B. rubra in Japan, expanding its known geographical distribution.
• The findings highlight the potential threat of this pathogen to Indian spinach cultivation in the region.