Hairy roots to test for transgenic nematode resistance: think twice

Hairy roots induced by Agrobacterium rhizogenes have been proposed as a versatile, easy and reproducible system for testing nematode resistance in crop plants. Here, A. rhizogenes was used to induce transgenic hairy roots on tomato (Lycopersicon esculentum) containing the LEMMI9 cDNA in sense and/or antisense orientation under control of a nematode responsive promoter. The purpose was to inhibit the expression of this gene that is strongly activated in the nematode-induced feeding sites in order to block their development and, thus, make the plants resistant. Several LEMMI9 transgenic lines produced fewer Meloidogyne incognita second-stage juveniles than the control lines, but a large variation in progeny was also seen among the control lines. Therefore, we recommend that several independent wild-type hairy root lines are generated and tested to obtain a solid control group for evaluating putative resistance constructs.