Callus concentration regulates somatic embryo production in orchardgrass suspension cultures

The effects of callus inoculation concentration and culture duration on somatic embryogenesis of orchardgrass, Dactylis glomerata L., were evaluated in suspension cultures of an embryogenic genotype, Embryogen-P. Somatic embryo formation was induced in liquid SH medium containing 30 μM dicamba (SH-30 and 1.5% casein hydrolysate; embryo development was in liquid SH medium without plant growth regulators (SH-0); and embryo maturation and germination occurred on solid SH-0 medium. Callus proliferation in SH-30 suspension cultures was greatest when callus was inoculated into the liquid medium at a relatively high concentration of 4% (4 g callus/100 ml medium), but the induction of somatic embryos was highest in this medium if the callus was inoculated at a lower concentration (&lt2%). In a second experiment, somatic embryo yield was highest when SH-0 development medium was inoculated with suspension culture callus at 0.1% concentration and declined markedly as inoculation concentration increased. Cell concentration is a critical factor in regulating the somatic embryogenesis response in orchardgrass suspension cultures.