First report of carrot root rot caused by Rhexocercosporidium carotae in the United States.
In March 2015, black irregularly shaped lesions up to 30 mm in diameter were observed on carrot roots that were placed in cold storage for 6 months in Wadhams, Essex County, New York, USA. Disease incidence was ∼5% and up to 30% of the tissue was affected on some roots. The crop was grown on Occum alluvial soil and no symptoms were observed at harvest. Small tissue pieces were excised from the edge of lesions and placed on 2% water agar in petri dishes and incubated at 20°C for 7 days in the dark, then transferred to V8 agar. Based on morphological characteristics, sequence analysis of the internal transcribed spacer gene and pathogenicity tests, the causal agent was identified as Rhexocercosporidium carotae. This is thought to be the first report of R. carotae in the USA.