Partial Resistance to Bacterial Wilt in Transgenic Tomato Plants Expressing Antibacterial Lactoferrin Gene

Expression of lactoferrin (LF) gene, a cationic iron-binding glycoprotein, was investigated in transgenic tomato plants (Lycopersicon esculentum Mill.). Resistance of the transgenic tomato plants to the pathogen (Ralstonia solanacearum Smith) causing bacterial wilt was also determined. Tomato line F7926-96, susceptible to bacterial wilt, was transformed with Agrobacterium strain C58C1 containing a plasmid construction carrying a modified LF cDNA. The introgression of LF cDNA into the susceptible tomato line was confirmed by Southern blot and the expression of full-length lactoferrin transcript and protein was also detected by northern and western blots, respectively. Based on resistance to kanamycin, a Mendelian segregation for a single locus insertion was observed in the T1 and T2 generations and all T1 and T2 plants resistant to kanamycin showed the single corresponding band of LF cDNA in Southern blot analysis. Two transgenic tomato lines inoculated with 1 × 107 and 1 × 108 colony-forming units (CFU)/mL with Rs isolate NC251 (K60, race 1) exhibited early resistance and subsequent susceptibility, while 44% to 55% of plants survived until maturity (fruit ripening) when inoculated with 1 × 105 CFU/mL in comparison with the fully susceptible tomato line. The latter resistance to bacterial wilt in transgenic tomatoes with the stable Mendelian segregation patterns for the LF gene suggests a potential new approach to consider for control of bacterial wilt of tomato. The possible value of this gene along with other plant genes to control bacterial pathogens is discussed.