First report of Alternaria leaf spot caused by Alternaria tenuissima on sugar beet (Beta vulgaris) in Minnesota, U.S.A.
In September 2018, foliar symptoms were first observed on older sugar beet (Beta vulgaris) leaves in about 3% of the cultivars in a coded variety trial in Renville, Minnesota, USA. Symptoms were dark brown circular or irregular spots on healthy plants. Initially, the lesions were confined within distinct parallel veins of the leaves but eventually expanded and coalesced across veins. In severely affected plants, the entire symptomatic leaves died. The causal pathogen was isolated and identified as Alternaria tenuissima based on morphological characteristics, molecular data (sequence analysis of the internal transcribed spacer (ITS)) and pathogenicity test. This is thought to be the first report of A. tenuissima causing leaf spot disease on sugar beet in Minnesota, USA.