Using callus derived from immature embryos, regeneration of viable plants was obtained in soybean (Glycine max (L.) Merr.). Depending on the composition of the medium, regeneration occurred via embryogenesis or via organogenesis. Embryogenesis resulted when embryos were plated on Murashige and Skoog (MS) medium containing 43 μM α-naphthaleneacetic acid. In work with the cultivar Williams 82, the addition of 5.0 μM thiamine HCl increased embryogenesis from 33% to 58% of the embryos plated. Addition of 30 μM nicotinic acid to the MS medium enhanced embryogenesis further to 76%. Organogenesis was obtained when medium containing 13.3 μM 6-benzylaminopurine, 0.2 μM and α-naphthaleneacetic acid and four times the normal concentration of MS minor salts was used. Histological studies of these cultures confirmed the organogenic and embryogenic nature of the cultures, by demonstrating the formation of shoot buds and somatic embryos, respectively. Similar responses were obtained in all 54 genotypes tested in this manner. The cultures retained the ability to regenerate complete plants for at least 12 months and 12-15 subcultures. Seeds have been obtained from several regenerated plants and when grown in the field these produced normal-appearing fertile plants.

Plants were regenerated from embryogenic and organogenic cultures derived from immature embryos of nine soybean (Glycine max L. Merr.) genotypes and extensive qualitative variation was noted in different regenerated families. Three lethal sectoral albinos were seen in the regenerated plants (R0). Variants observed in later selfed generations included twin seeds, multiple shoots, dwarfs, abnormal leaf morphology, abnormal leaflet number, wrinkled leaves, chlorophyll deficiency, partial sterility and complete sterility. The frequency of possible mutations ranged from 0 to 4% in R plants as determined by studies of corresponding R1, R2, R3 and R4 families. No significant differences were seen in the frequencies of possible mutations for embryogenic as compared to organogenic culture derived plants. Chlorophyll deficiency, sterility and wrinkled leaf traits were followed in two or more generations and showed that these traits were inherited stably. The known traits of this nature are controlled by single recessive nuclear genes. Other traits occurred more randomly and not in all generations. The genetic basis of the random variation is not known at the present time. This study indicates that heritable somaclonal variation does occur in tissue culture derived plants of soybean.

To identify genotypes which may give better plant regeneration responses in vitro, multiple shoots were induced from 155 Glycine max and 13 Glycine soja genotypes from maturity groups '000' to 'VII' on B5 medium supplemented with 1 or 5 μmol benzylaminopurine (BAP). The average number of shoots formed show genotype specific and hormone concentration specific responses, with number of shoots ranging from 1 to 12 for different genotypes. The results were reproducible with different seed lots of the same genotype and genotypes with similar genetic backgrounds responded in a similar fashion. No hybrid vigor was observed, except in one instance of F1 hybrids between low shoot producers where the number of shoots obtained were higher than either parent. The root forming ability of cuttings of soybean plants grown in vivo showed general agreement with shoot forming ability in vitro. The ability to form multiple shoots appears to be genetically controlled.

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Suspension cultures of soybean were initiated from hypocotyl or cotyledon callus tissue of several soybean genotypes. When these were grown on L2 medium with 0.4 mg/liter 2,4-D several genotypes produced numerous embryoids while others produced only a few such structures. Due to internal anatomy, no embryoid developed into a complete plant. A genotype's propensity to form normal appearing embryoids was correlated with the ability to proliferate shoots at the cotyledonary node on a medium with benzylaminopurine as determined in previous testing.