Inheritance of the resistance to Globodera rostochiensis pathotype Ro2 in potato

Nine advanced tetraploid potato clones with S. tuberosum ssp, tuberosum, S. tuberosum ssp, andigena, and S. vernei background were found to be highly resistant to Globodera rostochiensis pathotype Ro2. In order to characteriz e the inheritance of the resistance to Ro2 and determine the genotype of th ese Ro2-resistant clones, a series of testcrosses to susceptible S. tuberos um cultivars, as well as crosses between the resistant clones, were made. A total of 1081 seedlings corresponding to 18 families were grown, inoculate d with 3000 G, rostochiensis juveniles (J2), and evaluated by the root-ball method. To determine which genetic model best fit the data, goodness-of-fi t-test were performed. The analysis assumed tetrasomic inheritance under th e hypothesis that resistance is due to one locus with complete dominance. F rom the analysis of the data it is concluded that there is no consistent ev idence against the hypothesis that a single dominant gene is associated wit h the resistance to Ro2 and that the Ro2-resistant clones are simplex. In g eneral, the number of cysts observed on the root balls was low compared wit h the results of other studies, the results of the different inoculations w ere variable, and there was an excess of resistant plants. Possible explana tions for these observations are discussed.