INTERSPECIFIC SOMATIC HYBRIDS OF RUDBECKIA-HIRTA AND R-LACINIATA (COMPOSITAE)

Interspecific somatic hybrid plants between Rudbeckia hirta cv. Marmalade and R. laciniata cv. Irish Eyes were regenerated following the electro-fusion of mesophyll protoplasts of R. hirta with callus protoplasts of R. laciniata. A hybrid selection scheme was based on the fact that plant regeneration, from parental protoplasts of R. hirta, was via shoot regeneration of callus, and only via rhizogenesis for R. laciniata. The other half of the selection strategy was based on the presence of anthocyanin-pigmented roots; a characteristic of the R. hirta parent only. Somatic hybrids were regenerated, via rhizogenesis, alongside normal R. laciniata but were distinguished by the presence of pigmented roots (a feature of R. hirta). Hybrid plants had a floral morphology that was intermediate as compared to that of the two parents, with an expected somatic chromosome number of 2n=(2x+4x)=74. Pollen viability though was low. Esterase and peroxidase isozyme profiles confirmed the hybrid nature of the regenerated plants with pigmented roots, whilst chloroplast DNA restriction analysis showed that these hybrids had a R. laciniata chloroplast DNA. This demonstration of somatic hybridisation not only opens up the possibility of incorporating novel traits between such ornamental Compositae species, but provides a selection strategy based on rhizogenesis as the route to plant regeneration coupled with heritable pigmentation production of roots as a confirmatory hybrid marker. © 1990 Springer-Verlag.