GERMINATION OF ALFALFA (MEDICAGO-SATIVA L) SEEDS AND DESICCATED SOMATIC EMBRYOS .2. EFFECT OF NUTRIENT SUPPLEMENTS

The vigor of seedlings from desiccated somatic embryos of Medicago sat iva is less than in seeds and this limits the utilization of synthetic seeds for the establishment of plants in the field or greenhouse. To determine whether low seedling vigor was caused by a lack of protein o r carbohydrate reserves, the desiccated somatic embryos were imbibed o n agar media supplemented with sucrose and/or Murashige and Skoog (MS) salts. The combination of 10 g L(-1) sucrose and half-strength MS inc reased conversion, seedling fresh mass, shoot and root length, and num ber of leaves in the seedlings from somatic embryos at 14 d after imbi bition. Sucrose could be replaced by glucose or fructose, but not mann itol. Sucrose had a stimulating effect only if applied with MS salts a t imbibition, but not if it was applied at 7 d after imbibition. Neith er the amino acids, asparagine or glutamine, nor gibberellic acid had any effect on the germination or vigor of somatic embryos. Since the s ame stimulation was observed in seeds, the lack of nutrients does not seem to be the physiological factor limiting vigor, but germination on nutrient media may be a remedial way to enhance seedling development. Low seedling vigor therefore may be a consequence of inadequate or ab normal maturation of somatic embryos.