Plant Pathology

ABSTRACT Sunflower ( Helianthus annuus ) is an oilseed crop of global economic importance, and South Africa ranks among the 20 top producers worldwide. Sunflower production can be severely limited by fungal, viral and bacterial diseases. In South Africa, knowledge of viral diseases in sunflowers is particularly limited. During a disease survey of a field trial for a separate study, we observed symptoms not common in sunflowers in South Africa on several plants across the trial. This study aimed to identify the causal agent of these symptoms that were observed on sunflowers in two consecutive seasons at two experimental sites in South Africa (Pretoria and Potchefstroom). Illumina sequencing of total RNA from symptomatic leaves and reverse transcription‐PCR confirmation showed the presence of bidens mottle virus (BiMoV) in infected plants. BiMoV is a widespread potyvirus that is vectored by aphids, with weeds acting as viral reservoirs. The effects of the viral infection on the floral, morphological and yield traits in sunflowers were investigated. Pollen viability was reduced by 17.0%, plant height by 16.7%, leaf number by 12.3% and overall yield by 80.6%. This study suggests the potential for a significant impact from BiMoV infection on sunflower development and yield in South Africa. This is only the second report of natural infection of BiMoV in sunflowers and the first report of BiMoV in sunflowers in South Africa. We present preliminary evidence for yield losses; management strategies and disease progression need to be further investigated.