Light-induced systemic resistance in tomato plants against root-knot nematode Meloidogyne incognita

Plant immunity and defense responses are putatively stimulated by the quality of light spectra. To determine whether aerial light quality can modify the resistance of tomato plants to root pests, in this study, tomato plants inoculated with Meloidogyne incognita were exposed to purple, blue, green, yellow and red light from light-emitting photodiodes at 20 µmol m−2 s−1 photosynthetic photon flux density at the level of the canopy during night for 4 weeks and the number of nematode galls (incidence), plant growth, and defense responses were investigated. Among the studied light treatments, only the nightly red (R) light treatment reduced the number of nematode galls in the roots; this was associated with a 7.9-fold increase in the expression of PROTEINASE INHIBITOR PROTEIN 1 gene, a 17.4-fold increase in the transcript of PATHOGENESIS-RELATED CLASS 1 (PR1) gene, and a 25.4 % increase in the salicylic acid (SA) content in the roots. Furthermore, nightly R light treatment significantly recovered nematode-induced decreases in the light saturated rate of CO2 assimilation and plant fresh weight; however, the other light treatments did not have similar effects. These results indicate that the exposure of the shoot to R light at night induces systemic resistance in tomato plants against root knot nematodes in the roots, which is partly dependent on the jasmonic acid and SA defence pathways. Our study also suggests that exposure to R light at night could be a potential approach to control the nematode infestation in tomato which is particularly feasible for greenhouse production.