Prevalence and polymerase chain reaction detection of <i>Xanthomonas axonopodis</i> pv. <i>manihotis</i> causal agent of cassava bacterial blight disease in Osun state, Southwestern Nigeria

Abstract

Bacterial blight is one of the major diseases of cassava, caused by Xanthomonas axonopodis pv. manihotis (Xam) Bondar (Vauterin et al.) in Nigeria. It induces extensive necrosis on the leaves, twigs and stems systemically, which accounts for significant yield loss. Field survey for symptoms of cassava bacterial blight (CBB) disease was conducted across ten Local Government Areas (LGAs) notable for cassava production in Osun State. Disease incidence and severity were determined by visual examination and scoring of infected plants. Leaf samples obtained from 60 farmers' fields spread over the ten LGAs during the rainy season of 2016 were bioassayed using polymerase chain reaction (PCR) to detect the presence of the pathogen. Two Xam specific primers, 1525R (5'-AGGAGGTGATCCAGCC-3'). and 27F (5'-AGAGTTTGATC (A/C)TGGCTCA-3') were used to amplify 16s gene in total nucleic acid extracted from diseased leaf samples. Leaf samples from Ife North LGA had the highest incidence and severity of 76.10% and 4.5 respectively of CBB disease. PCR results showed high DNA concentration and presence of Xam in eight LGAs with infectivity varying from mild to highly infected. However, further studies will be required to determine the diversity among Xam isolates in the State in order to elicit appropriate control measures.

Keywords: Bioassay, Disease severity, Germplasm, Polymerase chain reaction, Xanthomonas axonopodis pv. manihotis