ROLE OF EXTRACELLULAR POLYSACCHARIDE AND ENDOGLUCANASE IN ROOT INVASION AND COLONIZATION OF TOMATO PLANTS BY RALSTONIA-SOLANACEARUM

Ralstonia solanacearum is a soilborne plant pathogen that normally inv ades hosts through their roots and then systemically colonizes aerial tissues. Previous research using wounded stem infection found that the major factor in causing wilt symptoms was the high-molecular-mass aci dic extracellular polysaccharide (EPS I), but the beta-1,4-endoglucana se (EG) also contributes to virulence. We investigated the importance of EPS I and EG for invasion and colonization of tomato by infesting s oil of 4-week-old potted plants with either a wild-type derivative or genetically well-defined mutants lacking EPS I, EG, or EPS I and EG. B acteria of all strains were recovered from surface-disinfested. roots and hypocotyls as soon as 4 h after inoculation; that bacteria were pr esent internally was confirmed using immunofluorescence microscopy. Ho wever, the EPS-minus mutants did not colonize stems as rapidly as the wild type and the EG-minus mutant. Inoculations of wounded petioles al so showed that, even though the mutants multiplied as well as the wild type in planta, EPS-minus strains did not spread as well throughout t he plant stem. We conclude that poor colonization of stems by EPS-minu s strains after petiole inoculation or soil infestation is due to redu ced bacterial movement within plant stem tissues.