Reduced Meloidogyne incognita infection of tomato in the presence of castor and the involvement of fatty acids

The plant parasitic nematode Meloidogyne incognita is a global pest that affects many crops, particularly in greenhouse. Castor (Ricinus communis L.) is an intercrop that has been suggested as a way of controlling M. incognita via an unknown mechanism. We hypothesized that root exudates of castor repel nematodes and reduce M. incognita damage to hosts in a tomato/castor intercropping system. This study aimed to identify the unique compounds in castor that reduce M. incognita damage by regulating nematode chemotaxis. Tomato (Solanum lycopersicum L.) intercropped with castor decreased nematode soil populations and reduced M. incognita infection of tomato roots by downregulating Mi-flp-18 and Mi-mpk-1 expressions. Two active components, palmitic acid and linoleic acid, released from castor were detected and quantified by gas chromatography-mass spectroscopy. Palmitic acid and linoleic acid repelled M. incognita and downregulated Mi-flp-18 and Mi-mpk-1 expressions at increasing concentrations (0.5 mM to 4.0 mM) in vitro. The root exudates from castor contain palmitic acid and linoleic acid, which repelled M. incognita chemotaxis and inhibited Mi-flp-18 and Mi-mpk-1 expressions in a concentration-dependent manner.