Growth and root-knot nematode infection of tomato are influenced by mycorrhizal fungi and earthworms in an intercropping cultivation system with leeks

In a greenhouse experiment, we investigated the influence of leek (Allium porrum) intercropping, mycorrhizal fungi and earthworms on the root-knot nematode infection by Meloidogyne incognita (RKN) and the growth and development of tomato plants (Solanum lycopersicum). Tomato plants were grown in pots, intercropped with leeks or in monoculture, and earthworms and/or arbuscular mycorrhizal fungi (AMF) were introduced. The effects of these two treatments on root-knot nematode infection and tomato plant growth and development were assessed i) by counting the galls induced by the nematodes and the number of egg masses on their roots, and ii) by measuring their height increase, shoot and root dry biomasses and flowering time. Tomato growth was increased with leek compared to the monoculture (e.g., +82% shoot biomass), probably due to a lower plant-plant competition, although a facilitation effect cannot be excluded. The presence of leeks did not reduce the number of galls (per g of root). The presence of AMF (Rhizophagus irregularis) increased the overall infection of M. incognita (e.g., +36% egg masses) and induced more galls with multiple egg masses in the leek-tomato association (+71%) but did not increase plant biomass. On the other hand, it increased plant height in presence of the compost earthworms (Eisenia andrei) compared to earthworms alone with RKN (+2%). It also delayed the flowering compared to RKN alone (+7.6 days in average). Competition between the two tomato plants in monoculture probably strongly impacted plant growth, flowering time and thereby the RKN infection, but leek-tomato interactions should be further examined. The overall increased number of multiple egg masses per gall in presence of AMF is contrary to its protective effect reported in the litterature.