Resistance to blackleg and tuber soft rot in sexual and somatic interspecific hybrids with different genetic background

Diploid interspecific hybrids from crosses between Solanum tuberosum haploids and S. canasense, S. multidissectum, and S. tarijense, along with tetraploid and hexaploid somatic hybrids S. tuberosum (+) S. commersonii, were screened for resistance to blackleg and tuber soft rot by Erwinia carotovora subsp. atroseptica and E. carotovora subsp. carotovora. Among the diploid hybrids, those involving clone mit la of S. multidissectum and tar 2b of S. tarijense yielded the highest number of genotypes resistant to both blackleg and tuber soft rot. By contrast, all the hybrids involving clone tar 11b of S. tarijense were susceptible to both bacterial diseases. As far as resistance of somatic hybrids is concerned, the most interesting genotype was the tetraploid one which showed resistance to both blackleg and tuber soft rot. Significant correlations were found between E. carotovora subsp. atroseptica and E. carotovora subsp. carotovora both in resistance to blackleg and in resistance to tuber soft rot, suggesting that resistance to the two subspecies is controlled by the same gene/s or that the relevant genes are linked. On the other hand, correlations between blackleg and tuber soft rot were never significant, indicating that different mechanisms may control resistance in tuber and stems. Alternatively, the resistance could be controlled by the same gene/s under a different spatial/temporal expression pattern. Twelve diploid sexual hybrids and one tetraploid somatic hybrid were selected for resistance to blackleg and/or tuber soft rot and for tuber characteristics.