FIG 7.

Loss of nitrate assimilation or EPS production reduced R. solanacearum tomato stem colonization and attachment to tomato roots. (A) Colonization of tomato stems following soil soak inoculation of tomato plants with wild-type UW551 (WT, ■), nasA mutant (□), nasA mutant coinoculated with UW551 wild type (▨), and nasA mutant coinoculated with epsB mutant (). Bacteria were quantified by dilution plating of ground midstem tissue 5 days after inoculation. Asterisks indicate significant differences from the WT (P < 0.05, t test; n = 9 plants/treatment; bars indicate the standard errors [nasA mutant error bars are too small to see]). (B) R. solanacearum attachment to tomato roots after 2 h of incubation with 2.5 × 10³ CFU/cm of root of wild-type UW551 (■), nasA mutant (□), or epsB mutant (). Three rinsed and blotted roots were pooled per biological replicate (n = 10 to 16 replicates), and each replicate was ground and dilution plated to quantify CFU/cm of root. As indicated below the columns, some treatments were combined with either an equal number of wild-type (WT) cells/root or 2.5 mg of cell-free EPS/cm of root (purified from wild-type cells grown in the presence of NO₃⁻). Bars represent the standard errors. Columns with different letters above them are significantly different from each other (P < 0.05, t test).