Temperature dependency of Pythium and Globisporangium spp. in causing soybean damping-off in Japan

Pythium aphanidermatum, P. coloratum, P. myriotylum, and Globisporangium irregulare (syn. P. irregulare), G. spinosum (syn. P. spinosum), and G. ultimum var. ultimum (syn. P. ultimum var. ultimum) are the causal pathogens of soybean damping-off in Japan. However, their temperature preferences have not been systematically investigated. In this study, we compared the soybean pathogenicity of these six species in low (15°C day/12°C night) and high (28°C day/25°C night) temperatures, under laboratory conditions (12h day/12h night). In the low-temperature treatment, G. irregulare, G. spinosum, and G. ultimum var. ultimum were highly pathogenic to the soybeans, whereas the other three species tested were weakly pathogenic. In the high-temperature treatment, P. aphanidermatum, P. myriotylum, G. spinosum, and G. ultimum var. ultimum were highly pathogenic, whereas G. irregulare was weakly pathogenic to soybean. P. coloratum showed no pathogenicity to the soybeans when compared to the non-inoculated control in the high-temperature treatment. These results demonstrate that the pathogenicity of P. aphanidermatum, P. myriotylum, and G. irregulare will be more temperature-dependent than those of P. coloratum, G. spinosum, and G. ultimum var. ultimum.