Variability in colony type and pathogenicity of the causal agent of sugarcane gumming Xanthomonas campestris pv. vasculorum (Cobb) Dye

Isolates of Xanthomonas campestris pv. vasculorum were obtained from leaves of various sugarcane cultivars in different regions of Reunion Island. The colonies formed in agar slant culture showed variable morphology, i. e., round (A type), fluidal and narrow (B type), or fluidal and broad (C type). Measurement of the symptoms produced by the different colony types in greenhouse-grown sugarcane plants demonstrated that they also differed in pathogenicity. Bacteria of A type were found to be less aggressive than those of B type, which themselves were less aggressive than colonies of C type. Degrees in pathogenicity were also noticed within A and B colony types. Statistical analysis of leaf streak length did not indicate any significant host-parasite interaction. Thus, the resistance of the cultivars studied appears to be non specific