Effect of polyethylene glycol and sugar alcohols on soybean somatic embryo germination and conversion

Polyethylene glycol 4000, mannitol and sorbitol were tested as supplements to a liquid Finer and Nagasawa medium-based histodifferentiation/maturation medium, FNL0S3, for soybean (Glycine max L. Merrill) somatic embryos of `Jack' and F138 or `Fayette'. Significant differences were found among types and levels of osmotica for their influence on quantity of mature embryos recovered, and on germination (root and shoot emergence) and conversion of embryos into plants. Supplementation of FNL0S3 with 5% polyethylene glycol or 1.5% sorbitol improved germination frequencies without limiting embryo histodifferentiation. Supplementation with 3% sorbitol resulted in a 9-fold increase in germination frequencies and a 13-fold increase in conversion frequencies of `Fayette' and `Jack' embryos. However, these improvements were accompanied by a significant, 22% reduction in fresh weight of mature embryos. Overall, 3% sorbitol was found to be the best of the osmotic supplements tested, resulting in 51 ± 5% conversion frequency (mean ± SE), as compared to 4 ± 1% in the control. Supplementation of FNL0S3 with 3% mannitol did not improve embryo maturation.