Attempts to regenerate plants from callus cultures of the lowbush blueberry, Vaccinium angustfolium ait

Sections of lowbush blueberry (Vaccinium angustifolium Ait.) fruits required both exogenous auxin and cytokinin for callus formation in vitro. The most effective auxincytokinin combination was 0.1 mg/ℓ 2,4-D + 0.1 mg/ℓ kinetin (or BAP). Autoclaved (but not filter-sterilized) tryptophan fulfilled the auxin requirement; on medium containing this substance there was a long lag period before the onset of : callusing, possibly because the tryptophan had to be converted to an active auxin. Callus formation in the berry sections declined with increasing age of the source fruits. There were clonal differences in the amount and appearance of callus formed on the berry sections. Callusing was better in dark- than in light-grown cultures. Many berry sections ripened in vitro. Berry callus subcultures were established on medium containing auxin and cytokinin. Autoclaved tryptophan fulfilled the auxin requirement, but callus growth was poorer than on medium containing 2,4-D or IAA. Tryptophan, but not IAA, promoted the development of tetraploid roots of normal appearance in the subcultures. Rooting declined over successive subcultures. Light and GA inhibited both callus growth and rooting. Coconut milk and yeast extract improved callus growth at some concentrations tested, but generally inhibited rooting. No organized multicellular structures other than roots were observed in the cultures. Stem callus subcultures required exogenous auxin (but not cytokinin) for growth. The appearance and growth rates of the subcultures were affected by the type of auxin present in the culture medium. Autoclaved tryptophan was ineffective as an auxin for initiation and subculture of stem callus. Light and GA inhibited callus growth. Kinetin, coconut milk, yeast extract and sequential passages on different media improved callus growth in some treatments. Roots formed in several subcultures, but no shoots or embryoids were observed. Some possible reasons for the lack of these structures in the subcultures are discussed.