RESPONSES OF NICOTIANA TABACUM CV. SR-1 TO XYLELLA FASTIDIOSA STRAINS

• Author(s): Bruening, George; Civerolo, Ed; Francis, Marta;
• Abstract: Nicotiana tabacum genotype (SR-1), was evaluated as a susceptible host for the bioassay of Xylella fastidiosa strains. Readily transformable N. tabacum cv. SR-1 plants were propagated in vitro. Transplanted plants were inoculated with various Xf strains. Inocula consisted of aqueous suspensions of bacterial cells harvested from 7-10 day old cultures on solid PWG medium. Inoculations were made by needle puncture through 20L of inoculum (10(8)bacteria/mL) placed in the axils of three basal leaves. Inoculated plants were maintained in a growth room (27-28(o)C, 12 hour photoperiod provided by GE High Output fluorescent lights) for 1 month, and subsequently transferred to a greenhouse. Generally, symptoms on plants inoculated with Xf strain Temecula-1 included necrosis at the margins with chlorotic zones extending toward the midvein after 6-8 weeks. Some affected leaves became cupped and curled downward. As infections became systemic, leaves that developed on new shoots were chlorotic and smaller. These symptoms did not develop on water-inoculated control plants. The presence of Xf in stems and leaf petioles of affected plants was confirmed by ELISA and real-time (RT) PCR. ELISA and RT-PCR assays of similar tissues from water-inoculated control plants were negative. Bacteria were observed by TEM and SEM in xylem cells in affected plants. No bacterial cells were observed in control plants. Xf was isolated from systemically infected tobacco leaf petioles from plants inoculated with Xf strain Temecula-1 and re-inoculated into grape plants cv. Ruby Seedless. Typical Pierces disease symptoms developed four weeks post-inoculation in the greenhouse, confirming the retention of pathogenicity of this strain to grapes after passage through N. tabacum cv. SR-1. N. tabacum cv. SR-1 plants with other Xf strains are being evaluated. Several factors, including plant age at the time of inoculation, method, and plant handling after inoculation, are being determined.
• Publication Date: Dec 2005
• Journal: 2005 Pierce's Disease Research Symposium