Resistance to Phytophthora infestans in somatic hybrids of Solanum nigrum L. and diploid potato.

In breeding for resistance to late blight, ( Phytophthora infestans Mont. de Bary), an economically important disease affecting potatoes, the search for new sources of durable resistance includes the non-host wild Solanum species. The aim of this work was to evaluate the resistance to P. infestans in the somatic hybrids between S. nigrum L. and diploid potato clone ZEL-1136. Sixteen somatic hybrids, their fusion parents, and three standard potato cultivars were screened for resistance to P. infestans in two types of tests-on whole plants and detached leaves-with two highly aggressive and virulent isolates of P. infestans, US8 and MP322. In the whole plant assay, the foliage of the somatic hybrids showed no symptoms of infection, while the foliage of the potato fusion parent and the standard cultivars was infected with P. infestans. In the detached leaflet assay, the breaking-down of resistance of the S. nigrum L. parent and the variable response of individual hybrid clones were noted. Nine S. nigrum L. (+) ZEL-1136 hybrids showed a resistance that was significantly higher than that of S. nigrum, while six clones expressed a resistance to P. infestans similar to that of S. nigrum. The results confirm the effective transfer of late blight resistance of S. nigrum into its somatic hybrids with potato.

Somatic hybrids Solanum nigrum (+) S. tuberosum: morphological assessment and verification of hybridity.

Somatic hybrids between the cultivated potato diploid hybrid clone, ZEL-1136, and hexaploid non-tuber-bearing wild species Solanum nigrum L. exhibiting resistance to Phytophthora infestans were regenerated after PEG-mediated fusion of mesophyll protoplasts. The objective was to transfer the late-blight resistance genes from the wild species into plants of the cultivated potato clone. From a total of 59 regenerants, 40 clones survived and have been maintained in vitro on hormone-free MS/2 medium. Thirty-two somatic hybrids were identified by their intermediate morphology (leaves of nigrum type and flowers of tuberosum type) and verified by flow cytometry and random amplified polymorphic DNA (RAPD) patterns. The RAPD analysis of nuclear DNA confirmed the hybrid nature of 29 clones. Flow cytometry revealed a wide range of ploidy in the generated hybrids, from nearly the tetra- to decaploid level. Most of the hybrid clones were stable in vitro, grew vigorously in soil, and set flowers and parthenocarpic berries. However, all of the flowering hybrids were male-sterile. Nine hybrid clones produced tuber-like structures in soil. The most vigorous flowering somatic hybrids were selected for assessment of the late-blight resistance.