Manganese superoxide dismutase in Meloidogyne incognita isolates selected for virulence on tomato.

Root knot nematodes (Meloidogyne spp.) are important pests of a wide range of crops, including tomato. Resistance of tomato to root-knot nematodes is conferred by the single dominant gene Mi-1, which is present in all commercially available resistant tomato cultivars, at present. However, several resistance-breaking populations are being collected world-wide. Two isolates coming from the same standard population of Meloidogyne incognita, one selected for virulence against Mi-1 and the other left avirulent, have been used in this study. Manganese superoxide dismutase activity (Mn-SOD) was higher in virulent infective juveniles compared with avirulent counterparts. m-RNA was extracted from those two isolates and converted into cDNA. Species-specific primers of Mn-SOD were used for PCR and one single PCR product was generated from each isolate (EMBL accessions nos. AM285679 and AM285680). Such products were sequenced and the deduced amino-acid sequence recognized as a mitochondrial dimeric manganese SOD. The amount of transcripts was quantified by realtime-PCR. The virulent isolate showed an amount of transcripts 4-fold higher than that present in the avirulent isolate. The up-regulation of manganese SOD gene, which was associated with a high activity of the enzyme, has been found to be a characteristic of pre-parasitic juveniles of M. incognita isolates selected for virulence on tomato.