The reproductive potential of root-knot nematodes Meloidogyne incognita is affected by selection for virulence against major resistance genes from tomato and pepper

Root-knot nematodes (RKNs, Meloidogyne spp.) are major plant pathogens of vegetables in most production areas, including the Solanaceous crops tomato and pepper. Due to the banning of chemical nematicides, current control strategies are mainly based on the deployment of resistance genes (R-genes), i.e., Mi(s) in tomato, Me(s) in pepper. These genes are effective against a wide range of RKN species, including M. arenaria, M. incognita and M. javanica, the most common species in temperate and tropical areas. However, the recent emergence of virulent populations able to overcome the resistance conferred by some of these R-genes may constitute a severe limitation to their use in the field. Research has been conducted to evaluate the durability of the Mi(s) and Me(s) R-genes, by comparing the reproduction of several laboratory-selected and wild virulent M. incognita isolates on both susceptible and resistant tomatoes and peppers. We first showed that the Me1 R-gene in pepper behaves as a robust R-gene controlling avirulent and virulent Me3 or Mi-1 isolates. We also confirm that virulence is highly specific to a determined R-gene on which selection has occurred, thus allowing the alternance of R-genes in the rotation as an effective mean to improve soil health. Another significant experimental result is the observation that a reproductive fitness cost is associated to nematode virulence. The adaptative significance of trade-offs between selected characters and fitness-related traits suggests that, although the resistance can be broken, it might prove durable in some conditions if the virulent nematodes are counterselected in susceptible plants, which has important consequences for the management of plant resistance in the field.