The fate of extracellular polysaccharide from Pseudomonas phaseolicola in leaves and leaf extracts from halo-blight susceptible and resistant bean plants (Phaseolus vulgaris L.)

Abstract

Purified extracellular polysaccharide (EPS) from Pseudomonas phaseolicola was infiltrated into the mesophyll of bush bean leaves (Phaseolus vulgaris L.). The EPS disappeared from the intercellular spaces of the halo-blight resistant breeding line 02 12 h after infiltration. Simultaneously, the visible water-soaked spots had vanished. By contrast, the intercellular spaces of the halo-blight susceptible cultivar Red Kidney were still completely filled with EPS 3 days after infiltration, and the water-soaked leaf-areas persisted. The EPS formed a stable network in the intercellular spaces of Red Kidney, whereas small floccules were observed in the incompatible system.In vitro studies showed that the intercellular fluid (IF) from the trifoliates of breeding line 02 partially degraded the EPS, whereas IF from cultivar Red Kidney did not. EPS which had been incubated with IF from resistant leaves completely lost its capacity to induce persistent water-soaked spots. It is concluded, therefore, that the resistance of bean leaves towards persistent water-soaking caused by bacterial EPS was due to enzymatic degradation and inactivation of the introduced EPS.