OCCURRENCE, DISTRIBUTION AND CHARACTERISATION OF Xanthomonas axonopodis pv. dieffenbachiae, CAUSAL ORGANISM OF BACTERIAL LEAF BLIGHT OF COCOYAM IN NORTH WEST NIGERIA

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OCCURRENCE, DISTRIBUTION AND CHARACTERISATION OF Xanthomonas axonopodis pv. dieffenbachiae, CAUSAL ORGANISM OF BACTERIAL LEAF BLIGHT OF COCOYAM IN NORTH WEST NIGERIA

Abstract:

Field surveys were conducted during 2014 wet season in three Local Government Areas each of Kaduna, Kano and Katsina States in North West Nigeria to determine the occurrence and distribution of bacterial leaf blight of cocoyam. A total of 81 cocoyam fields were surveyed in the three States. Sampling was done using a five, 2×2 m2 quadrat in each of the nine fields assessed per Local Government Area. Disease incidence recorded in each field showed that the highest incidence of 93.7 % in Kaduna State was obtained in Kudan and the least 16.6 % in Giwa Local Government Areas. In Kano State, the highest 30.0 % and lowest 10.4 % incidence were recorded in Kiru and Bebeji Local Government Areas respectively. With respect to disease severity, Kudan and Giwa Local Government Areas in Kaduna State recorded the highest 45.3 % and the lowest 6.3 % respectively while Kiru and Bebeji Local Government Areas in Kano State recorded the highest 12.7 % and lowest 2.7 % respectively. Bacterial leaf blight was not found in any of the surveyed cocoyam fields in Katsina State. Bacterial isolates obtained from the diseased samples were used for pathogenicity and hypersensitive reaction (HR) tests on cocoyam and tobacco plants respectively and the results indicated that six isolates induced blight symptoms on cocoyam and elicited HR reactions on tobacco. Biochemical tests such as catalase tests, pectolytic tests, amylolytic tests, fluorescence on KB medium and production of acid from glycerol were carried out on the isolates and found that isolates were amylolytic and pectolytic. Furthermore, all the isolates were Gram negative, motile, oxidase negative, catalase positive and did not fluorescent on KB medium and produced no acids from glycerol. For molecular characterisation, a nearly full length of the 16S rDNA gene of selected isolates was PCR amplified using 16S rRNA primers (27F and 1492R) and referenced amplicons were sequenced at the Eurofins Genomics Company, Eurofins MWG vii Operon LLC, Huntsville, Alaska, USA using Sanger sequencing. BLAST results of sequenced genes showed 98-100% homology to Xanthomonas axonopodis pv. dieffenbachiae. Maximum likelihood phylogenetic trees constructed for the 16S rDNA gene sequences revealed isolates were identical to the X. axonopodis pv. dieffenbachiae reference strains AC1 and XADK. Generally, all the isolates obtained were X. axonopodis pv. dieffenbachiae. This is the first report of X. axonopodis pv. dieffenbachiae causing bacterial leaf blight in cocoyam fields in North West Nigeria and the first report on molecular characterisation of the pathogen in Nigeria.

OCCURRENCE, DISTRIBUTION AND CHARACTERISATION OF Xanthomonas axonopodis pv. dieffenbachiae, CAUSAL ORGANISM OF BACTERIAL LEAF BLIGHT OF COCOYAM IN NORTH WEST NIGERIA

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