Evaluation of detection methods for cowpea bacterial blight caused by Xanthomonas axonopodis pv vignicola In Nigeria

The detection of cowpea bacterial blight in seed lots of cowpea (Vigna uniguiculata) is important for developing management options. Cowpea seeds were collected from five locations within two agro ecological regions in Nige-ria. Various modifications to the plating and soaking methods were adopted to evaluate extraction of bacteria from seeds and selected isolates from the seed lots were subjected to various pathogenicity tests with the objective of find out the best method of detecting the cowpea bacterial blight pathogens in seed lots. All seed assay experi-ments and pathogenicity tests were laid out in a completely randomized design (CRD) with three replications. Per-centage seed infection was significantly higher in Zaria, Minjibir (northern guinea savannah) and Iseyin (forest transition zone) compared to the other production locations in both plating and washing assay methods. The seed coat alone was the most (p≤0.05) colonized part of the seed by the pathogen followed by the cotyledons while em-bryo was the least colonized. Pod inoculation was the most effective pathogenicity test followed by inoculation of young plants, while inoculation of the excised cotyledons, stems and petioles were not reliable in expressing symp-toms. Detection of Xanthomonas axonopodis pv vignicola (Xav) is better made with methods that breach the seed coat or using the seed coat alone. Detached pods are just as efficient and takes less time to get results compared to inoculation of young plants for determining pathogenicity of Xav isolates.