Transgenic Expression of<i>EFR</i>and<i>Bs2</i>Genes for Field Management of Bacterial Wilt and Bacterial Spot of Tomato

Field trials were conducted at two locations in Florida to evaluate transgenic tomato expressing the ELONGATION FACTOR TU RECEPTOR (EFR) gene from Arabidopsis thaliana, the Bs2 gene from pepper, or both Bs2 and EFR (Bs2/EFR) for managing bacterial wilt caused by Ralstonia solanacearum and bacterial spot caused by Xanthomonas perforans. Expression of EFR or Bs2/EFR in the susceptible genotype Fla. 8000 significantly reduced bacterial wilt incidence (50 to 100%) and increased total yield (57 to 114%) relative to lines expressing only Bs2 or the nontransformed Fla. 8000 control, although the marketable yield was not significantly affected. Following harvest, surviving symptomatic and nonsymptomatic plants were assessed for colonization by R. solanacearum. There were no significant differences in the population at the lower stem. Interestingly, in the middle stem, no bacteria could be recovered from EFR or Bs2/EFR lines but viable bacterial populations were recovered from Bs2 and nontransformed control lines at 10² to 10⁵ CFU/g of stem tissue. In growth-chamber experiments, the EFR transgenic tomato lines were found to be effective against seven different R. solanacearum strains isolated from the southeastern United States, indicating utility across the southeastern United States. In all of the bacterial spot trials, EFR and Bs2/EFR lines had significantly reduced disease severity (22 to 98%) compared with the Fla. 8000 control. The marketable and total yield of Bs2/EFR were significantly higher (43 to 170%) than Fla. 8000 control in three of four field trials. These results demonstrate for the first time the potential of using the EFR gene for field management of bacterial wilt and bacterial spot diseases of tomato.