Tuber quality and soft rot resistance of hybrids between Solanum tuberosum and the incongruent wild relative S. Commersonii

Tetraploid BC3 hybrids between sexually incompatible species Solanum commersonii and S. tuberosum were characterized for tuber quality (stolon length, tuber eye depth, chipping color from 3-month storage at 5 C, and specific gravity) and soft rot resistance traits. For all analysed morphological traits, except stolon length, genotypes resembled the S. tuberosum phenotype. On average, the specific gravity of selected genotypes was quite high (1.087), and 12 of them had a value >1.090. As for chip-processing ability, 4.8% of genotypes chipped well directly from cold storage, and 14.3% after reconditioning. All but one of these genotypes also possessed a high specific gravity of tubers. Variability was found for resistance to Erwinia carotovora subsp. carotovora. In particular, 24% of hybrids had a rotted area diameter < 4 mm and were classified as resistant. The average percentage of commersonii-specific markers still present in the BC3 hybrids was 22%, ranging from 9% to 37%. Genotypes combining good qualitative tuber traits with a wild genome content lower than the average value of the population were selected for further breeding efforts. The importance of molecular-assisted selection is discussed.