The effects of Nematode Infection and MI-Mediated Resistance in Tomato (Solanum Lycopersicum) on Plant Fitness

The Mi gene in tomato (Solanum lycopersicum) is a single, dominant resistance (R) gene that confers resistance against several species of insects and root-knot nematodes. This study examined the impact of root-knot nematode infestation and the plant growth and reproduction of near-isogenic tomato cultivars with and without Mi. The objectives of this experiment were to examine the potential fitness costs and benefits of the R gene-mediated herbivore resistance, and to explore the role of nematodes as a selection pressure favoring plants that carry Mi. Mi-mediated resistance dramatically reduced nematode reproduction on tomato. In the presence of nematodes, plants that carried Mi produced larger fruits and greater foliar biomass than susceptible plants. Both resistant and susceptible plants, however, were able to compensate for heavy nematode infestation, and neither genotype showed a significant reduction in yield or estimated lifetime seed production in response to infestation. Therefore, Mi-mediated resistance did not provide a fitness benefit to the plants under the infestation level tested. Seeds from plants that carried Mi also had lower germination rates than seeds from susceptible plants, suggesting that there may be a metabolic fitness cost associated with Mi-mediated nematode resistance.