MOLECULAR CHARACTERIZATION OF Xanthomonas axonopodis pv. vignicola MORPHOTYPES ISOLATED FROM COWPEA GROWN IN THREE AGROECOLOGICAL ZONES IN NIGERIA

Abstract

Cowpea (Vigna unguiculata (L.) Walp) is a drought-tolerant crop and a vital food legume in the tropical Savannah zones of Africa. It is a preferred staple food due to its high protein and digestible carbohydrate content, along with essential micronutrients. However, the production of cowpea is hindered by pests and diseases, including bacterial blight caused by Xanthomonas axonopodis pv vignicola (Xav). This study employed molecular characterization to confirm the presence of different morphotypes and distinguish between isolates of Xav collected from cowpea samples in 81 locations across 9 states in Nigeria, covering 5 agro-ecological zones. The isolates were classified into two groups based on their morphological characteristics on nutrient agar medium, varying in color from light yellow to brownish yellow. Genomic DNA extraction was carried out on all the Xav isolates, involving centrifugation, resuspension, incubation, phenol-chloroform-isoamyl alcohol extraction, ethanol precipitation, and resuspension. DNA concentration was measured using a DU-65UV spectrophotometer, and quality was checked via electrophoresis on a 1% agarose gel. Polymerase chain reaction (PCR) analysis using forward and reverse primers was carried out on the Xav isolates genomic DNA. The amplified DNA PCR products of Xav morphotype, was extracted from low melting agarose gel and sequenced using ABI 3130 DNA Sequencer at INQABA Biotec International. Phylogenetic analysis of the obtained sequences confirmed differences between the two morphotypes, validating the results from conventional identification methods. These findings suggest that the presence of both types of isolates, as confirmed through conventional and molecular characterization, is necessary for the manifestation of typical symptoms of bacterial blight in cowpea.