X. Campestris pv. dieffenbachiae, the Causative Agent of Common Leaf Blight Disease in Dasheen (Colocasia sp.) and Cocoyam (Xanthosoma sp.)

Dasheen (Colocasia sp.) and cocoyam (Xanthosoma sp.) are nutritionally and medically rich tuber crops that grow readily in tropical and sub-tropical regions where favorable growing conditions exist. However, they are affected by numerous pests and diseases. In the present study E. chrysanthemi pv. dieffenbachiae, X. campestris pv. dieffenbachiae, P. syringae and a non-fluorescent Pseudomonas, are associated with the common leaf blight disease. However, the causative agent, X. campestris pv. dieffenbachiae, was found to be host specific producing symptoms of common leaf blight disease infection on dasheens and cocoyams and a hypersensitive response on the non-host pepper (Capsicum chinense). DNA fingerprinting analyses of X. campestris pv. dieffenbachiae indicated sequences from the hypersensitive response gene, hrpB6 and hrpG, and the ORF1-ORF2 of a pathogenicity gene of X. campestris pv. glycines. The hrp cluster is conserved among pathovars of X. campestris and is responsible for infection. The hrp cluster can be used as a molecular probe for assessing X. campestris pv. dieffenbachiae infections. The insertion of the avirulence (avrBs3) gene into X. campestris pv. dieffenbachiae increased the hypersensitive response of pepper and induced resistance in dasheen and cocoyam.