Occurrence and Properties of Copper-resistance in Plant Pathogenic Bacteria.

Abstract

Copper-resistance was analyzed with 189 strains of plant pathogenic bacteria that belonged to the genera Pseudomonas, Xanthomonas, Erwinia, Agrobacterium, Clavibacter and Curtobacterium. For the assay, CuSO4 or copper compounds (copper fungicides) were incorporated into Bacto potato-dextrose agar (PDA). Bacteria that grew on PDA containing CuSO4 at concentrations of 1.25mM or more were arbitrarily categorized as copper-resistant. The minimum inhibitory concentrations (MIC) of CuSO4 on the copper-PDA medium were one to two times greater than with casitone-yeast extract-glycerol agar medium, and 100 times greater than with aqueous solution. Copper-resistant strains were detected in many of the plant pathogenic bacteria, particularly in pseudomonads. The high MIC of CuSO4 were specifically found in members of the rRNA II subgroup of Pseudomonas such as P. cepacia and P. gladioli. Resistance to CuSO4 did not necessarily correlate with resistance to copper fungicides. In P. cepacia, P. gladioli, P. syringae pv. actinidiae, A. radiobacter and A. tumefaciens, copper-and streptomycin-resistances were concurrently found in the same strains. Copper-resistant strains of A. tumefaciens belonged to biovar 1 (all of 3 strains), biovar 2 (1 of 8 strains) and biovar undetermined (1 of 2 strains). A copper-resistant strain of A. radiobacter also belonged to biovar 1. Six strains of A. vitis tested were all copper-sensitive.