Somatic hybridization between anther-derived dihaploid clones of potato (Solanum tuberosum L.) and the identification of hybrid plants by isozyme analysis.

Green mesophyll protoplasts of the dihaploid potato line 198∶2 (Solanum tuberosum L.) were fused with herbicide-bleached mesophyll protoplasts of the dihaploid potato line 67∶9 using a polyethylene glycol protocol. Heterokaryons were identified under a fluorescence microscope using the dual fluorescence of carboxyfluorescein-stained, herbicide-bleached protoplasts and the autofluorescence of green mesophyll protoplasts. About 20% of the protoplasts survived the fusion treatment, and the fusion frequency was 3%-4%. Unfused and fused protoplasts were mass cultured for 6 weeks after which vigorously growing calli were selected and transferred to shoot regeneration medium. Somatic hybrids were identified by a combination of five isozyme markers, and the ploidy level was determined by flow cytometry. Out of 15 calli that regenerated shoots, 6 plants derived from 2 different calli were identified as hexaploid somatic hybrids, while one morphologically deviant plant from a third callus was identified as a mixoploid that had lost some enzyme markers after 4 months of culturing.