Natural hybridization between Globodera rostochiensis and G. pallida

An experiment was conducted in pots which offered the maximum of possibilities for Globodera rostochiensis and G. pallida to hybridize. An inoculum of G. pallida cysts was mixed with a five-fold larger inoculum of G. rostochiensis pathotype R01/4 and was used with a cultivar resistant to G. rostochiensis. The F1 cysts were characterized and compared with pure G. pallida by three different methods. In tests with groups of five J2's on plants growing in Petri dishes, a slightly greater proportion of juveniles from the F1 cysts failed to penetrate the roots and develop than from the pure G. pallida control. The results indicated about 9 to 18 % of hybrids. Tests with WPG2 monoclonal antibody with Elisa demonstrated that some cysts contained hybrids with a proportion difficult to estimate. Examination of the internal transcribed spacers of the ribosomal gene following amplification using PCR reaction and cutting with restriction enzymes clearly demonstrated the presence of hybrids. The relative proportion of the hybrids, calculated from an analysis of a sample of 30 individual F1 cysts, showed that one was a complete hybrid, three were partly hybrids, one was a pure G. rostochiensis and the remainders were pure G. pallida. These results clearly demonstrated that natural hybridisation between these two sibling species is possible and probably occurs in natural conditions. Consequently, there is a risk that hybrid populations may eventually emerge.