Diagnosis and Characterization of the Citrus Canker Pathogen (Xanthomonas axonopodis pv. citri) Strains in Ethiopia

Abstract

Citrus canker, caused by Xanthomonas axonopodis pv. citri, is a very destructive disease that is listed as a quarantine organism in many countries. Occurrence and distribution of the disease in the Rift Valley o f Ethiopia had been reported. Studies were conducted with the objective of monitoring recent spread of the disease in the country, identifying, characterizing and determining the genetic diversity of 20 Ethiopian strains on the basis of their pathogenecity, biochemical, physiological, and molecular properties. Diagnosis was carried out using polymerase chain reaction (PCR). Pathogenecity tests, biochemical and physiological characterizations, insertion sequence ligation mediated polymerase chain reaction (IS-LM- PCR) and multilocus variable number of tandom repeat analysis (MLVA) were carried out following standard procedures established for same. Citrus canker was observed to spread to
central and northern parts of the country. Pathogenecity tests indicated canker symptoms on Mexican lime (Citrus aurantifolia) and alemow (Citrus macrophylla) leaves and not on sweet orange (Citrus sinensis) and grapefruit (Citrus paradisi). The expected 492-bp amplification products were produced with DNAs of all Ethiopian strains. In the biochemical and physiological characterization, all strains showed similar reactions. All four primers in the IS-LM-PCR did not indicate satisfactory polymorphism within the strains. On the other hand, MLVA analysis indicated polymorphism between the tested Ethiopian strains and those from international collections. On the basis of pathogenecity, biochemical and physiological, tests, ISLMPCR, and MLVA analysis results, the Ethiopian strains were grouped into a cluster comprising of X. citri pv. citri pathotype A* and is epidemiologically important on Mexican lime and alemow.