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 T 1 and T 2 generations and all T 1 and T 2 plants resistant to kanamycin showed the single corresponding band of LF cDNA in Southern blot analysis. Two transgenic tomato lines inoculated with 1 × 10 7 and 1 × 10 8 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 × 10 5 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.