Synergistic activity between Bacillus thuringiensis Cry6Aa and Cry55Aa toxins against Meloidogyne incognita

Plant-parasitic nematodes are the most destructive group of plant pathogens worldwide and are extremely challenging to control. Some Bacillus thuringiensis crystal proteins are highly toxic to the plant-parasitic nematode Meloidogyne incognita. In this study, the nematicidal crystal proteins Cry6Aa, Cry5Ba and Cry55Aa were tested against M. incognita to select the best toxin combination for its management. The results showed that a combination of Cry6Aa and Cry55Aa showed significant synergistic toxicity against M. incognita, and the highest synergistic effect (five times the expected toxicity of the two toxins calculated from their separate toxicities) was observed when they were combined in a 1:1 ratio. Furthermore, ligand blot analyses of the interaction between total proteins of M. incognita and the three toxins showed many different signal bands, indicating that there is a range of host proteins with which the toxins can interact. One explanation of the observed synergism is that the toxins damage the host in diverse ways, and they may thus act cooperatively and thereby show greater toxicity in combination. Our discovery provides an effective strategy for controlling M. incognita by using a combination of Cry6Aa and Cry55Aa.