The root-knot nematode (RKN) Meloidogyne incognita is a major soil parasite of pepper crops in greenhouses in Southeast Spain. Due to the limitations of the use of soil fumigants, grafting plants on resistant rootstocks (R-rootstocks) has become an important alternative to chemical nematicides. The repeated use of R-rootstocks can bring about the selection of virulent populations capable of overcoming resistance. We carried out a six-year investigation on resistant rootstocks in a naturally M. incognita infested greenhouse, and found that two successive years of growing plants grafted on R-rootstocks Atlante (ATL) were sufficient to overcome resistance (galling index 1.5 and 5.6 in the first and second years respectively). A large variability was observed between several R-rootstocks. Two R-rootstocks (C19 and Snooker) behaved like ATL while two others (Terrano and DRO 8801) were not infected by RKN. Laboratory studies with the same R-rootstocks, inoculated with two nematode isolates (avirulent and virulent against ATL) confirmed the greenhouse results, indicating that some rootstocks may be infested by virulent populations and others may not. It suggests that different R-genes, which are differentially overcome by RKN, have been introgressed into the rootstocks. This may have consequences for the management of resistant rootstocks in the field.

The aim was to confirm the depressive effect on pepper plants grown in non-disinfected soils and to ascertain the possible specificity of fatigue with the goal of establishing strategies for disinfecting soils with a broad spectrum of fumigants. Soil samples were taken from six greenhouses that had been used for different numbers of years to grow a monoculture of pepper and which received different disinfestation treatments (methyl bromide, 1,3-dichloropropene+chloropicrin, biosolarization) and one which received no treatment. Every soil sample was splitted in three fractions. The first fraction was disinfested with methyl bromide (MB), the second with steam at 120ºC by autoclaving (A), and the third was not disinfected (ND). Pepper plants were cultivated in pots. Celery and lettuce were also cultivated in the same conditions to ascertain the degree to which soil fatigue was specific. In 87.5% of the 16 soil variants, the plants cultivated in the disinfected soil fractions (MB or A) were higher than those grown in the non-disinfected fractions. However, in the case of celery and lettuce, the plants cultivated in ND were higher than those cultivated in MB or A. The results show that the fatigue accumulated in the soil of the pepper monoculture was highly specific towards this crop, suggesting that rotation with other crops is an advisable agronomic practice in order to recover the soil productive capacity.