Archivio Journal of Plant Pathology

Abstract:

Common burdock (Arctium lappa) also called cockle button and stick button is a biennial weed species in the family Asteraceae. In 2012, angular leaf spots have been observed on this species in Firuzkuh. The symptomatic sample of burdock were collected and the causative bacterium was isolated on sucrose nutrient agar (NAS). The resulting circular, mucoid, yellowish colonies were subjected to biochemical tests in comparison with Xanthomonas gardneri IBSBF 1782. All isolates were Gram-negative and were positive for casein hydrolysis and Tween 80 hydrolysis. In addition, they utilized inulin, maltose and malate but not glutamate and myo-inositol (Schaad et al., 2001). DNA was isolated from the isolates by the alkali lysis method (Arabi et al., 2006) and used in PCR with gyrB primers (Young et al., 2008) to amplify a fragment of this gene. The amplified fragments were sequenced and the nucleotide sequences for isolate for gyrB (GenBank accession No. KP892557) were compared with those deposited in GenBank. Sequence compression indicated that the isolates have the highest identity (99% similarity) with Xanthomonas gardneri. Pathogenicity tests to burdock and their hypersensitive reaction on geranium (pelargonium x hortorum) were proven. Leaves of burdock plants were inoculated by injection with bacterial suspensions, diluted to contain approximately 106 colony-forming unit (cfu) per milliliter. All strains of the bacterium isolated from burdock induced leaf spot symptoms. Disease symptoms appearing within 7 days post- inoculation, were similar to those caused by natural infections in the field. This is the first report on the pathogenicity of this species on burdock.