INHIBITION OF CALLUS DEVELOPMENT FROM PROTOPLASTS OF LYCOPERSICON-PERUVIANUM BY EXTRACELLULAR POLYSACCHARIDES OF CLAVIBACTER-MICHIGANENSIS SUBSP MICHIGANENSIS

Clavibacter michiganensis subsp. michiganensis, the causal agent of bacterial canker of tomato, produces phytotoxic extracellular polysaccharides (EPS). To evaluate the potential use of EPS in a selection system at cellular level, its effects were studied on protoplasts of susceptible and partially resistant genotypes of the wild tomato species Lycopersicon peruvianum. The number of protoplasts that developed into minicalli was used as a parameter for toxic effect. Protoplasts of the partially resistant genotypes were not, or only slightly, affected by the EPS. The development of minicalli from protoplasts of some susceptible genotypes was significantly inhibited by EPS, however no absolute correlation between susceptibility at plant level and sensitivity of protoplasts to EPS was found. A putative effect of the phytotoxic EPS on plant cell membranes was tested for protoplasts of a bacterial canker sensitive L. peruvianum genotype. This was studied by measuring sucrose uptake, depending on membrane-bound processes, in the presence or absence of EPS. Since no alteration in sucrose accumulation was measured, apparently EPS has no direct effect on the membranes of EPS sensitive protoplasts during the early phase of culture. More information about the mode of action of EPS and the insensitivity of protoplasts of some genotypes is necessary, before considering application of EPS for in vitro selection. © 1990.