First report of pythium root rot on aeroponically grown sweetpotato caused by Pythium myriotylum in Louisiana.
Increased demand for virus-tested sweet potatoes (Ipomoea batatas) has led to the use of aeroponic propagation. In autumn 2017, Bayou Belle and Beauregard sweet potatoes growing in aeroponics in Franklin Parish (Louisiana, USA) became stunted with mild interveinal chlorosis after warm weather, which was associated with pale to dark brown soft rot of the secondary roots. All aeroponic plants became affected, but plants subsequently regenerated secondary roots. Based on morphological characteristics, molecular data (sequence analysis of the internal transcribed spacer and cytochrome oxidase subunit 1) and pathogenicity test, the causal agent was identified as P. myriotylum. Pythium ultimum, P. scleroteichum, P. spinosum and P. aphanidermatum have been associated with mottle necrosis of storage roots and/or root rot of fibrous roots of sweet potato in the field. This is thought to be the first report of P. myriotylum on sweet potato, and of root rot of sweet potato grown in aeroponics.