In-vitro morphogenesis of corn (Zea mays L.). II. Differentiation of ear and tassel clusters from cultured shoot apices and immature inflorescences

The objective of this research was to study the in-vitro morphogenetic pattern of corn (Zea mays L.) shoot tips excised from aseptically-grown seedlings, and of explants of axillary shoot buds, immature tassels and ears (staminate and pistillate inflorescences) obtained from greenhouse-grown corn plants. The seedling shoot tips and immature ears first regenerated clumps of multiple shoots within four weeks of culture on Murashige and Skoog (MS) basal medium supplemented with 500 mg/L casein hydrolysate (CH) and 9.0 micromolar N6-benzyladenine (BA). Multiple shoot clumps were also differentiated from spikelets of immature tassels cultured on MS medium containing 500 mg/L CH, 4.5 micromolar BA and 0.45 micromolar 2,4-dichlorophenoxy acetic acid (2,4-D). All these multiple shoot clumps in turn differentiated clusters of ears after further four subcultures at four-week intervals under light on MS medium supplemented with 500 mg/L CH and 2.25, 4.5, 9.0 or 18 micromolar BA. Axillary shoot buds readily differentiated clusters of ears within four weeks of the initial culture on these media. Secondary and tertiary ear clusters were initiated following subculture of primary ears on MS medium containing 500 mg/L CH and 4.5 or 9.0 micromolar BA. Most of the ear primordia developed into ears with well-developed ovaries and styles on subculture on MS medium containing 500 mg/L CH and 1.0 micromolar BA. Corn kernels were obtained after pollination of in-vitro-formed ears with pollens collected from greenhouse-grown corn. These kernels germinated in vitro and developed into mature corn plants in the greenhouse. Clusters of tassels were also differentiated in darkness from the multiple shoot clumps after six months successive subcultures but the spikelet primordia of tassels failed to develop fully under the in-vitro conditions tested. Somatic embryos arose directly from spikelet primordia of young tassels or ears on MS medium containing 500 mg/L CH and 4.5 micromolar 2,4-D, or indirectly from calli derived from spikelets of young tassels and ears on MS medium containing 500 mg/L CH and 9.0 micromolar 2,4-D.