Isolation of atypical wheat-associated xanthomonads in Algeria

Bacterial leaf streak and black chaff are important bacterial diseases of wheat, which have been reported to be caused by Xanthomonas translucens. In 2016, symptoms of bacterial leaf streak and black chaff were observed in Algeria, at experimental wheat breeding stations and in farmers' fields under sprinkler irrigation on two wheat cultivars, 'Hiddab' and 'Simeto'. Yellow Xanthomonas-like bacterial colonies were isolated from plant material, including leaves, spikes and post-harvest crop residues. Initial characterisation using biochemical, physiological and pathogenicity tests identified the bacteria as Xanthomonas. Diagnostic PCR targeting the 16S-23S rRNA intergenic region indicated that the strains were X. translucens, a clade-1 xanthomonad. However, partial DNA sequences of the housekeeping genes gyrB and rpoD revealed that the strains belong to clade 1, but likely represent a new Xanthomonas species that has not been previously described on wheat or other Gramineae. The most closely related strain, NCPPB 2654, was isolated from a bean plant in the United Kingdom in 1974. Further characterization is required to clarify the taxonomic status of the Algerian Xanthomonas isolates from wheat, and to determine their host ranges and impacts on plant cultivation.