Bacterial leaf streak caused by Xanthomonas vasicola pv. vasculorum, a disease that might threaten European maize production

Plant diseases caused by Xanthomonas species affect many different crops worldwide. The species Xanthomonas vasicola currently includes four pathovars: arecae, musacearum, vasculorum (Xvv), and holcicola (Xvh). Of these only Xvh has a validly published name, although the others have been proposed. Maize (Zea mays) is the most widely grown cereal in the world. Bacterial leaf streak of maize caused by Xvv was first reported in South Africa in 1948 and was not reported anywhere else until 2014 when it was identified in Nebraska, USA; this disease then spread rapidly and is now present in 10 US states. Recently it has also been reported in some regions of Argentina and Brazil. This disease is not currently present in Europe, but should be considered as a potential threat to maize crops. At Fera, artificial inoculations on a range of maize varieties grown in the UK indicate wide susceptibility to this pathogen. The main host of Xvv is maize, but evidence has shown that other monocot species like oat and rice are also hosts. The most likely pathway of entry in Europe will be on seed, although there are only a few reports of seedborne infections. By sequencing Xvv isolates from South Africa, the US, Brazil, and Argentina, and comparing sequences with publicly available data, we aim to determine what is the most likely origin of the infections observed in South America and use this to inform a plant protection strategy for the UK.