ARS | Publication request: PYTHIUM STEM CANKER ON GRAIN AMARANTH

Submitted to: American Phytopathological Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: March 19, 2002
Publication Date: June 1, 2002
Citation: Block, C.C., Van Roekel, J.W., Robertson, L. 2002. Pythium stem canker on grain amaranth. American Phytopathological Society Annual Meeting. 92:S8

Technical Abstract: An unusual stem canker was observed on mature grain amaranth plants (Plainsman cultivar) in Nebraska and Missouri production fields during August 2000 and in Iowa plots during 2000 and 2001. Dry, tan cankers with thick black borders, similar in appearance to blackleg of crucifers, developed near the soil line. The cankers often spread 15-45 cm up the stems. In attempts to identify the causal agent, we isolated several Phoma-like fungi along with Pythium spp. Each isolate was tested for pathogenicity on greenhouse plants by drilling small holes in the stems, introducing fungal mycelium, and sealing with petrolatum. Plants were observed for 6 weeks, but only the Pythium isolates caused disease, usually within 4-7 days. Canker symptoms were also demonstrated on plants grown in potting mix amended with the Pythium cultures. All of the isolates were identified as P. aphanidermatum, which has been reported from amaranth, but is usually associated with a soft, basal stem rot. One Pythium isolate was derived from a basal stem rot, but did cause stem canker symptoms when inoculated onto Plainsman plants.