Introgression and stabilization oferwinia tuber soft rot resistance into potato after somatic hybridization ofsolanum tuberosum ands. brevidens

Resistance to potato tuber soft rot caused byErwinia carotovora was transferred fromSolanum brevidens to the cultivated potato over the course of four backcross generations originating from a somatic hybrid. Soft rot reactions were determined via a tuber plug inoculation method developed during the course of these experiments. Soft rot resistance was highest in the somatic hybrid (only ca. 20% of tubers and plugs showed evidence of severe rotting) and lowest among progeny of control potato x potato crosses (ca. 80% of tuber plugs showed severe rot). Backcross generations involving somatic hybrids were intermediate in their reaction, and resistance stabilized to about 60% of tuber plugs showing severe rot in the BC₂ through the BC₄. Reciprocal crosses showed no difference in the inheritance of soft rot resistance, indicating that neitherS. brevidens norS. tuberosum donor cytoplasm had a significant effect on the expression of resistance. Crosses between BC₃ siblings where noS. brevidens genetic markers were detected but resistance was segregating demonstrated a dosage effect for soft rot resistance. We conclude that introgression of soft rot resistance has occurred and that at least one locus responsible for resistance inS. brevidens now resides in theS. tuberosum genome.