SummaryCreation from 4x hybrid clones from protoplast fusion of 2x clones of potato was evaluated. Besides combined nuclear genomes, composition of the cytoplasm significantly influenced the phenotypic traits of hybrid clones. To ascertain the influence of parental cytoplasm on the success of protoplast fusion and regeneration of hybrid plants, data from 74 fusion combinations of 50 dihaploid clones were analyzed. The majority of dihaploid breeding clones belonged to the cytoplasm types Wet, TI3 and W~/.When the closely related mt types et, 13 and "/were used, fusion combinations had a better combining ability compared with more distantly related cytoplasms 8 and e. Fusions containing the same mitochondrial type (homofusions) were not superior to closely related mitochondrial types. However, homofusions of cytoplasm type Wet yielded significantly more hybrids than homofusions of type TI]. In general, parental cytoplasm types had little impact on the fusion combining behaviour. Thus the cytoplasm type of the fusion parents is not a suitable marker for predicting the combining ability in protoplast fusion experiments.

Mesophyll derived protoplasts of Solanum khasianum Clarke and S. aculeatissimum Jacq. were fused by electrofusion and resulted in interspecific hybrids. In total, 249 calluses were obtained from which more than 65% produced shoots. From the regenerated plantlets 45% could be identified as hybrids by chromosome counts (4x = 48) and esterase isozyme pattern. Most hybrids showing intermediate phenotypic characteristics, had a normal flower morphology with fertile pollen and produced fertile berries. More than 80% of the seeds germinated.