Characterization of somatic embryogenesis in Pelargonium x hortorum mediated by a bacterium

Several cultivars of hybrid seed geranium (Pelargoniumxhortorum Bailey), pr eviously shown to be recalcitrant in culture, produced somatic embryos at h igh frequency when explants were ce-cultivated with a morphogenesis promoti ng bacterium. This bacterium was isolated as an in vitro contaminant from c ultures of geranium seedling explants and identified as belonging to the ge nus Bacillus and species circulans. Go-cultivation of hypocotyl explants wi th the bacterium promoted somatic embryo formation and improved both the fr equency and quality of somatic embryos. In the cultivar Ringo Rose, the lea st responsive among the cultivars screened, the embryogenic response was mo re than four times that of axenic cultures. Nearly 70% of these embryos con verted into plantlets, while the somatic embryos induced under axenic condi tions developed poorly and plantlet formation was inconsistent. Among the d ifferent treatments of bacterial culture tested (autoclaved culture, cultur e filtrate, sonicated bacterial culture, sonication of bacterial culture fo llowed by filtration, HPLC fractionation of crude bacterial lysate), only t wo HPLC fractions promoted embryogenesis to a marginal degree. Go-cultivati on of the explants with bacterium during the first week of induction was cr ucial for obtaining high-frequency embryogenesis, indicating the role of ba cterial stimuli during the induction process.