Expression of a plant cystatin confers partial resistance to Globodera, full resistance is achieved by pyramiding a cystatin with natural resistance

Constructs based on a cysteine proteinase inhibitor (cystatin) from sunflower and a protein engineered variant of a rice cystatin (Oc-IDeltaD86) conferred similar levels of resistance on potato plants to Globodera spp as chicken egg white cystatin (CEWC) under the control of CaMV35S. The level of resistance on challenge by 6.5 viable eggs Globodera spp g(-1) soil in a small scale field trial was similar to that provided by the natural partial resistance of cv. Sante. PCR of an internal transcribed spacer region of the ribosomal cistron of the nematode genome established that the challenging population was a mixture of G. pallida and G. rostochiensis with no evidence of a differential effect of the transgenic resistance on the reproductive success of the two species. Transformation of Sante and the South American cultivar Maria Huanca with CaMV35S/CEWC raised the status of both cultivars from partial to full resistance in this study. The results establish the potential of plant cystatins and demonstrate an additive effect of expressing CEWC with natural resistance genes.