Bacterial growth and phytoalexin elicitation in soybean cell suspension cultures inoculated with Pseudomonas syringae pathovars

Abstract

Two commonly used media for the culturing of numerous plant tissues, 1-B5 and 1-B5C, were tested for their ability to support bacterial growth. No significant growth of strains representing four of the six major genera of phytopathogenic bacteria occurred in 1-B5 liquid medium, in contrast to 1-B5C, making 1-B5 highly suitable for studies of most phytopathogenic bacteria—plant tissue culture interactions. Both compatible and incompatible strains of the soybean bacterial leaf pathogen Pseudomonas syringae pv. glycinea plus strains of the bean pathogens P. syringae pv. phaseolicola and pv. syringae , induced production of the phytoalexin glyceollin in soybean cv. Mandarin cell suspension cultures. Glyceollin production was elicited without a concomitant hypersensitive response (HR). Induced glyceollin production by cell suspension cultures declined as the number of culture transfers increased. There was no expression of resistance to incompatible strains of pv. glycinea , pv. phaseolicola or pv. syringae by the suspension cultured soybean cells. This was indicated by: (1) highest glyceollin production by soybean cell line Sb-2 after inoculation with a compatible pv. glycinea strain, (2) greater growth of pv. syringae strains than pv. glycinea and pv. phaseolicola and (3) an incompatible pv. glycinea strain grew as well as compatible pv. glycinea strains. Of several bacterial strains which elicited an HR on soybean leaves in vivo , only pv. syringae strain Y30 caused a rapid decline in viability of suspension cultured soybean cells. Various bioassays were used in an attempt to determine if production of the pv. syringae Phytotoxin syringomycin was responsible.