In vitro development of inflorescences from switchgrass nodal segments

Immature inflorescences are an important explant source for initiating in vitro cultures in gramineous species. The objective of this study with switchgrass (Panicum virgatum L.) cv. Alamo was to produce axenic inflorescences from nodes cultured in vitro. The top nodal segments from tillers in the two to four node stage of greenhouse grown plants were surface sterilized, split longitudinally, and plated with the cut surface in contact with Murashige and Skoog (MS) medium containing 30 g L(-1) maltose. 6-Benzylaminopurine (BAP) was added in concentrations of 0.0, 5.0, 12.5, or 25.0 mu M. After 2 to 5 wk culture, panicles were produced with fully developed spikelets and perfect terminal florets. Panicles produced on medium without BAP were between 5 and 9 cm long and the number of spikelets ranged between 50 and 200. Panicles produced on medium with 5.0 to 25.0 mu M BAP had a shorter rachis (2-5 cm) and branches, but contained more spikelets (200-700). Young spikelets obtained after 20- to 30-d culture of nodes, were used as explants for regeneration experiments. Calli were initiated from spikelets plated on MS solid medium with 30 g L(-1) maltose, 22.5 mu M 2,4-dichlorophenoxyacetic acid (2,4-D) and 5.0 mu M BAP. They were later transferred to MS medium without growth regulators, where thousands of regenerants developed through somatic embryogenesis and organogenesis. The procedure is highly efficient for producing multiple sterile explants from a single genotype for use in various in vitro culture experiments.