Host Range and Virulence Characterisation of Xanthomonas vasicola pv. vasculorum Causing Bacterial Leaf Streak of Maize in Nigeria

Bacterial leaf streak of maize, caused by Xanthomonas vasicola pv. vasculorum, was first confirmed in West Africa in 2017 and has since been reported in multiple Nigerian states. Yet comprehensive host range studies and virulence characterisation of Nigerian isolates remain absent, limiting national biosecurity risk assessment and breeding responses. This study characterised the host range and virulence of 40 X. vasicola pv. vasculorum isolates collected from symptomatic maize farms across four geopolitical zones of Nigeria. Isolates were characterised by multi-locus sequence typing targeting gyrB, rpoD, and fusA housekeeping loci. Host range assays tested inoculation of 15 Poaceae and 10 Solanaceae species. Virulence assays on nine maize inbred lines quantified disease severity and lesion expansion rate under controlled inoculation conditions. All 40 isolates were pathogenic on maize, producing characteristic water-soaked streaks on susceptible hosts within 4 to 7 days. Host range testing confirmed pathogenicity on sorghum, pearl millet, and sugarcane but not on tested Solanaceae species. Multi-locus sequence typing resolved isolates into two sequence types, ST-1 and ST-2, with ST-2 isolates consistently more virulent in quantitative virulence assays. Maize inbred lines CML444 and TZEI23 showed significantly lower lesion severity scores, providing candidate sources of tolerance for use in resistance breeding programmes. These findings establish a nationally relevant virulence and host range reference dataset that fills a critical gap in Nigerian plant bacteriology. Keywords: Xanthomonas vasicola, bacterial leaf streak, maize, virulence, Nigeria.